This is about my third thread on this issue, but this time I'm offering a reward, a steak dinner. I'll send a $25 Outback gift card to the first person can solve the mystery.

Scenario: I drive to the track, go through the usual routine of parking, checking things over, setting tire pressure, get in the staging lanes, etc.
I get up to the starting line and do a good burnout with no trouble. Stage car, everything is still fine. Light turns green and I go, by 5000 rpm in first gear my fuel pressure drops to near nothing. If I stay on it and shift to 2nd, it falls on its face completely with no fuel pressure. As soon as I let off it regains fuel pressure and recovers.

This ONLY happens at the track. I can hammer it all day on the street with no trouble. I can pull out of the track directly after a failed pass and wind out 1st and 2nd gear to 6500 and the pressure holds rock steady. I have a 'test strip' near the house where I can wind it out from a stop to 100+mph without a hitch. The car behaves perfectly on the street.
The only clean passes I have made at the track was the one trip where I trailered the car and ran it only long enough to open the thermostat before running it. That's when I yielded the time in my sig.
I've replaced/upgraded every component of the fuel system except for the fuel pump (a carter 172). It's 1/2" from the tank to the regulator, with a 3" section of 3/8" from the regulator to the carb. I have much of the setup insulated with heater hose to help keep the fuel cool. I keep at least 1/2 a tank in the car at the track to make sure the pickup stays in the fuel. Basically this fuel system should be able to feed 2 1/2X the horsepower I make. I would think if something was inadequate, it would show up no matter where the location.

The only difference I see between the street and the track is the amount of time the system has to 'heat soak'. I've taken every precaution though and last time I even wrapped the intake/carb/regulator with an ice-water soaked towel for several minutes before I ran. The fuel pressure looked great until I hit it, and it was gone before I could wind out first gear.
I see people with much faster cars and seriously ghetto fuel systems run without problems though. I don't get it, it's literally as if the car has simply refused to run at the track, and only at the track. :(

I think you are emtying the float bowls during your burnout & the pump can't recover in time. Are you doing burnouts on the street & making a pass right away? I think you need more fuel pump or better flow from the source.(tank/cell) OR your floats are set too low & the traction at the track & the floats are bottoming out.

I think you are emtying the float bowls during your burnout & the pump can't recover in time. Are you doing burnouts on the street & making a pass right away?

I havn't tried doing a burnout on the street before testing it. That's not easy to do on the Mickey Thompson DR's, I'd probably break something trying to burn them out without a water box :). That sounds plausible though, particularly since my Q-Jet doesn't hold as much fuel in the bowl as a Holley.

Like I said the only thing I havn't replaced or upgraded is the fuel pump. What would work better than a Carter 172? Perhaps mine isn't working 100%?

how much gas in the tank? I had a similiar problem in a 69 I used to have, when it hooked hard below a 1/3 tank the gas would slosh to the rear of the tank and un cover the pickup. never did it on the street only at the track. made sure I always had 1/2 tank or more- problem solved

how much gas in the tank? I had a similiar problem in a 69 I used to have, when it hooked hard below a 1/3 tank the gas would slosh to the rear of the tank and un cover the pickup. never did it on the street only at the track. made sure I always had 1/2 tank or more- problem solved

yeah, i got that covered :). 1/2 tank of fuel plus 1/2" fuel pickup.

I had a Qjet years ago. When it was real hot out I had an occasional problem. At about half track the car would die. I would let the pedal up and got out of the secondaries and it would be fine.

Certainly appeared like the secondary well was losing fuel.

I put a "corvette" pump on it and didn't have any problems after that.

I think I have read about some mods to increase the supply to the secondary well on a Qjet, but it has been many years since I messed with one.

....(a carter 172). It's 1/2" from the tank to the regulator, with a 3" section of 3/8" from the regulator to the carb.

You are running a Carter 172 mech pump with a regulator?
They don't use a regulator do they?

You are running a Carter 172 mech pump with a regulator?
They don't use a regulator do they?

The 'default' pressure is about 8 psi, which is too much for the Q-Jet. I regulate it to about 6 psi. Much more than that and I'll get 'nozzle drip' at idle.

A q-jet doesn't have a 'secondary' well, the secondary jets are at the rear of the main fuel well. There are two secondary accelerator circuit wells that supply fuel to the secondary accelerator circuit, but you want to be very careful in enlarging the supply to them.

Jets uncovering because of the sticky track treatment! Get some jet extensions should cure the problem. Now send me a PM for the gift card:)

What kind of regulator? Return bypass ( 3 line ) or deadhead ( 2 line ) if a deadhead that could be the problem.

What kind of regulator? Return bypass ( 3 line ) or deadhead ( 2 line ) if a deadhead that could be the problem.

I don't run a return line, and my regulator is non-bypass. How does that affect it?

Jets uncovering because of the sticky track treatment! Get some jet extensions should cure the problem. Now send me a PM for the gift card:)

Jet extensions in a Q-jet?

I would move the fuel pressure gauge to the inlet side of the regulator to see if it's the pump causing the problem. I would also reduce the fuel pressure at the carb to less than 4#, mine works great at 3.5#.

Where is the fuel pressure gauge located that you are reading zero pressure?

It seems to me that after the burnout he's getting good bite and leaning out, whereas on the street he's not getting it to hook up as hard so it doesn't lean out. Or you might have to increase your fuel pressure.

onovakind,
You're correct.

Where is the fuel pressure gauge located that you are reading zero pressure?

It comes directly off the regulator, and the guage sits just behind the hood against the windshield.

I'd try a Holley on it, or just a different carb, it would be a process of elimination.

Ken,i had the same thought of his car hooking better at track and low fuel level in tank going to rear uncovering fuel pickup when launching.

Brian,i had seen the video of your car running good #'s(12's) at the track and it didnt fall on its fac. It ran very well and i could easily hear it up to like over 6k rpms in each gear without falling on it's face at all,what happened?

Has it always done the fall on it's face thing and i just didnt notice it in the video sound clip or is this a new problem the showed up after Sean modified your carb for better idle with the big cam as you stated in a recent post?

Other thoughts of things to chk/try to fix your fuel starvation problem at higher rpms if you have not already done so:

Remove the smaller in carb fuel filter and run a large high flow inline filter and if that fixes it great,if not then try this.

I have also seen the heavier stock fuel pump rods float at 5k & higher rpms so i would install a lighter one rated for above 6k. This is because the heavy stock pump rods can casue pump arm float at lower then 6k rpms which i have experiecned 1st hand mult times in the past.

Carter pumps are very good but i would still replace the one you have while installing the new light higher rpm pump rod since a new pump in not too expensive and your current pump drops fuel pressure at times. Dropping pressure like you stated is a sign of pump arm float at higher rpm or could just be a sign of a bad pump too.

If removing the in carb fuel filter and installing a new pump & lighter high rpm pump rod dont fix it then i would opt to drop the tank and replace the sock on the fuel puckup.

The sock on fuel pick up could be partially clogged limiting fuel flow on hard launches and under the higher load

Since the tank was out at this point i would also opt to install a larger fuel line pickup just in case you find out later on you need to upgrade to a larger fuel line from the tank to the motor so you can avoid having to remove the tank a 2nd time.

Pull the q-jet and have the float lvl adj for the highest possible fuel lvl without casuing flooding or running rich issues.

Last thought,you had posted a while back that sean had modified the carb idle circut in an attempt to improve your idle with the lagre cam your runing.

Did the problems start after he did that mod to the carb?

If yes then maybe Sean accidnetially adj the float lvl to low after reassembling the carb after he did the mod or something to do with that mod casues the carb to empty out easier or faster then it did prior to the special mod. Or maybe the mod he made for better idle has some kind of an affect when you leave the line hard and fuel goes to rear of float chamber.

So if this problem did show up after Sean's mods i would definately call him to see exactly what he did to the carb and to see what he thinks could be the issue/s at this point and a possible fix for it.

Let me/us know how you make out.

Scott

I'm having a similar problem, and I run a Holley 650 DP, Carter 172, and no regulator. About 1 pass out of every 4, the car quits pulling at the top of 1st gear, shifts to 2nd, and picks back up. It kills about 3 tenths of ET, but curiously the MPH is about the same as a good pass. Needless to say, it's difficult to win a bracket race this way. I had just about convinced myself it was vapor lock, but re-routing the fuel line away from the radiator and heater hoses didn't seem to help the problem. I run a -8 Earl's fuel filter between pump & carb, and no bronze inlet filter on the carb. I don't really want to install a fuel pressure gauge, but maybe I need to. I'm also wondering if my valve springs may be weak.

Scott, the videos were of the one trip that I mentioned where I had clean passes. That was the one time I trailered the car instead of driving it to the track, and ran it only long enough to warm up the engine before making a pass. Every time I drive it to the track, i get the bad behavior.

I've already done some of the things you mention, I recently upgraded the fuel pickup to 1/2". The problem was there before I sent the carb back to Sean, and I've talked to him about it. He didn't know of anything related to the carb or the way he set it up that would cause the issue. I asked specifically about the float level.

Also, I don't think it's really a 'starvation' issue. I can wind it to 6500+ on the street and see the pressure holding rock steady on the guage. If something was happening at high rpms I'd expect to see it on the street as well. 6500 is 6500, no matter where you're doing it.There is something about the track that triggers the problem, and when it happens the pressure starts falling as soon as I hit it, not just at high rpm. Maybe it's the burnout, the launch, or the heat that builds up sitting in the staging lanes.
I dunno, and I'm tired of paying $15 to go there, make 1/2 of one pass, then coming back home to try the next 'fix'. I'm about ready to just quit taking it to the track, period. :(

Jets uncovering because of the sticky track treatment! Get some jet extensions should cure the problem. Now send me a PM for the gift card:)

I said that first

It seems to me that after the burnout he's getting good bite and leaning out, whereas on the street he's not getting it to hook up as hard so it doesn't lean out. Or you might have to increase your fuel pressure.

see my first post

There is no bowl resivior in a Q jet, the super stock guys run big ( # 10) fuel line to act as a resivior. it could be heat soak affecting the pump, perhaps causign a vapor lock issue

A larger diameter pickup tube and a not-so-good pump is a bad combo'. The pump is having to do more work. Even moreso under acceleration.

Buy a new pump.

Then, buy a new carb. ;)

BTW, I went 105MPH in the 1/4 mile with stock 3/8" fule line (including original pickup and sock) and a Q-jet carb'. All supplied by a MAllory comp 140 fuel pump.

Some guys were close but they didnt hit on your problem. This is a old timey problem you dont hear about much anymore because people are using bigger and stronger fuel pumps. The 1/2 " fuel line is your culprit. The mech pump is made to pull which is fine but the fuel in a 1/2 " line is too heavy to pull under the force of the car leaving at the track. The fuel literally stalls in the line. Switch back to a 3/8 line from the tank to the regulator and your problem will go away. In the older days it used to take 2 holley blue pumps to operate a 1/2" line to the front, or else the fuel would stall.Or install a big electric in the rear that has enough motor to push it under the g force of the launch.

How about one of these? http://store.summitracing.com/partdetail.asp?autofilter=1&part=QFT%2D30%2D204&N=700+4294925239+4294839053+4294891547+400990+115&autoview=sku :D

It sounds like my next step should be a new a fuel pump. If that solves the issue, dreis454 will get the prize since he first suggested the pump isn't refilling the fuel bowl fast enough after my burnout.

I use the big Holley mechanical pump with a stock 3/8" fuel line and am running 12.0's with no fuel delivery problem at all. I am using a Holley carb. though.

My car originally had a 307 with 5/16" fuel line. When I bought the cam for the new engine, UDHarold said to run 1/2", so that's what I did. I don't see why that would be a bad thing, so long as the fuel pump could handle it.

" so long as the pump can handle it " that is the key. Common knowledge is it is easier to push fuel againt the force from the launch than to pull it. A 1/2 line is more likely to stall the fuel and when it stalls it can literally pull the fuel back towards the tank away from the pump under the force of the launch, the fuel is wanting to stay put as the car drives forward.The 3/8 line is not as likely to have this problem due to it having less mass and weight of the fuel wanting to remain still as the car moves forward. Thats what's happening .

Ooopss thought he had a Holley.

Brian,you say when you trailer the car it runs fine at the track but when you drive the car there it pulls the fall on it's face stuff.

Is are your metal fuel lines getting heated up by headers and water pump etc enough so that at times its close to vapor locking?

That would explain why it runs fine when trailered and the underhood temps are not near as hot as when you drive the car to the track.

Just to test this theory out wrap all the exposed fuel lines from f/pump to carb with al foil or some kind of insulation and then drive the car to the track.

You could also bring a few of those freezeable bricks to the track to place on intake and fuel lines to cool things down when in the staging lanes.

If the problem goes away then you know a partial (not full)vapor lock is your problem which i have seen happen before. It doesnt have to be harrible hot out for this to happen,iv'e seen it happen in high 70-very low 80 deg weather.

This would also explain why you cant get the motor to fall on its face while trying it on the road. Thats because your driving the car keeping the motor just cool enough to stay below partial vapor lock temp but when you drive it to the track and then stop the fuel lines/pump/carb heat soak and thats when they get hot enough for partial vapor lock and the trouble starts.

So try the al foil warp around all fule lines and fuel pump to test this theory out and let us know how it does and if i win the dinner award.(YEH!!!)

I know it will look like crap but it's all in the road to traking down your problem which i think could really be this partial vapor lock thing.

Scott

Scott, a heat issue has always been my first suspicion, but I've never been able to prove it or solve it. My thought was that driving on the street I kept enough fresh fuel flowing to keep it cool, but parked at the track or sitting in the staging lanes, it gets in a heat soak condition.
I've taken alot of extra precautions that most people don't take against that though, to no avail. My lines aren't any closer to anything hot than the other cars out there, and I've wrapped most of it in heater hose.

Brian,ok,if your sure you have the heat thing covered then its time for a new pump and lighter pump rod if your not already running one.

But i get the impression your not fully satisfied that its not a heat issue and neither am i.

I say this becasue if it was a bad pump or heavy stock pump rod float or some other fuel obstruction casuing it the motor would do the same thing on the road leaving hard from a dead stop if it hooked well or at the track at the same approx rpm but it doesnt do that.

The key clue here is it doesnt do it while driving on the street hitting same rpm lvl's when motor is a little cooler even leaving from a dead stop on the street like at the track and if the problem was the larger 1/2 inch fuel line it would do it both on the street and track which it doesnt do. But it does it only at the track when you drive the car there and then it heat soaks when you stop which it doesnt do on the street while driving and air is passing through the engine compartment keeping things just cool enough to stay below partial vapor lock temp.

Just to put the heat thing to rest once and for all bring water and or ice to the track and cool off the fuleline/pump just before a run to make sure its not a heat issue.

I know you have rubber hose over the meal lines but remove the rubber hose and just dump some ice water/ice over all the lines and pump just before a run and see what happens.

If it still falls on its face then you know for sure its not a heat thing but if it runs ok try another run with cooling things off just prior to the 2nd run.

If that 2nd run with ice cooled fuel lines does ok then try letting the motor idle for a few mins to heat it back up with hood down and leave it down in the staging lanes too with as much idling as possible to get it hot or better yet hit the street for a 15-20 mins mins (to simulate driving to the track) and then return to the track for a 3rd run.

Do a good full burnout then try it again and if it falls on its face on the 3rd heated up run you know whats going on for sure and what to go after and if not then you can for 100% sure rule out heat as the demon and go for a new pump & lighter rod at that point and go from there.

Scott

I don't think heat is at all. I'm really thinkin it's a supply problem either at the tank (stock 5/16 pickup) or as I said in my first post on page one....The pump can't recover fast enough for a pass after the burnout.

It doesnt take a fuel pump very long at all to recover and refill a very small q-jet foat bowl.

There is a very important piece of info Brian gives about the problem that being missed here which is it only does it when he drive the car to the track and not when he drives it on the road and tries to do strip runs on the street no matter how hard he runs it.

Biran also stated when he trailered the car to the track and did his burnouts as usual and runs the car/motor it did not fall on its face then,its only when he drives it to the track and then races. But it doesnt do it on the street no matter how hard he pushes it which i think is becasue the temp is kept low enough while driving the car but at the track it heat soaks after the drive to the track then waiting in the staging lane/s to run & doing burnouts. Then things can get just hot enough to go into partial vapor lock cutting off fuel flow under load just after doing the burnouts with a heat soaked fuel system in partial vapor lock at that point.

It may very well not turn out to be a heat thing but he can put that to rest real quickly if he drops some ice water over the fuel lines /pump/and intake just prior to running and if it does ok then he knows it's heat but if not any better after cooling things off then i would definately go for a new pump and lighter pump rod for avoid any chance of pump arm float at higher rpms and go from there at that point.

I have seen when in a partial vapor lock situation a new more powerfull sucking and pumping fuel pump can sometimes overcome the partial vapor lock making you think the pump was the issue when its really running hot but not hot enough for a full vapor lock shutting the motor down completely.

Scott

VAPOR LOCK - disruption of fuel movement to a gasoline engine carburetor caused by excessive vaporization of gasoline. Vapor lock occurs when the fuel pump, which is designed to pump liquid, loses suction as it tries to pump fuel vapor. The engine will usually stall, but in less severe cases may accelerate sluggishly or knock due to an excessively lean fuel mixture. Automotive engines are more likely to experience vapor lock during and acceleration that follows a short shutdown period. Vapor lock problems are most likely to occur in the late spring on unseasonably warm days, before the more volatile winter grades of gasoline have been replaced by the less volatile spring and summer grades (see volatility). Vapor lock can also occur in other types of pumping systems where volatile liquids are being handled.

I'll have to vote with Scott on this one.

ARE TODAYS REFORMULATED FUELS WITH 10% ETHANOL MORE PRONE TO VAPOR LOCK THEN FUELS OF THE PAST WITHOUT IT?

I ask this because a few other people in T/C have also been experiencing vapor lock type symptoms this summer more so then i have seen in the past and was wondering about the ethenol in the fuel possibly making it more liable/prone to vapor lock.

I thought maybe the ethenol might go to a vapor/gas state at a slightly lower temp then the older formula fuel without the ethenol in it,is this correct or am i wrong on that?

I know there are a few sharp chemist's or people that work in the petroleum industry here in T/C that could answer this quesation.

Scott

Well I suck at this stuff but have you tried a new gas tank cap?

I'm sure he's getting better traction at the track, I've always raced with a full tank of fuel, running mid 10's with a stock pickup (no sock) in the tank. I would put an electric pump in the back, a pusher to the front pump that you only have to use at the track, that worked for me until the 505 was installed then the mech. pump became a restriction to the Comp140. I would also put a phenolic or wood spacer under the carb to get it off the hot intake. Surely you don't have one of those in carb fuel filters? I learned a very long time ago, take em out and throw them as far as you can, they are nothing but trouble.

If heat is suspected, would it not be easier to try and heat soak the car on the side of the road then duplicate the problem on the street? (On a deserted road with zero traffic of course) If the problem does not reoccur on the street due to heat, then I would look at the extra traction caused by track causing starvation.

Steve

I would move the fuel pressure gauge to the inlet side of the regulator to see if it's the pump causing the problem. I would also reduce the fuel pressure at the carb to less than 4#, mine works great at 3.5#.
Really? I run 6 psi at idle, and at WOT she works down to about, yeah, 3.5 lbs. range, which scares me. Got a nice Holley 110 mech pump.

Wow, this is all great information! I hope someone else can benefit as well.

So I think the consensus is one of two main causes

1)Heat soak causing a vapor lock condition (my own suspicion all along as well). Any suggestions for a permanent solution to this? I'm going to have problems just using ice water, because I can't do that in the staging lanes and be dripping water when I get up to the starting line. I can do it in the pits, but after spending 15 minutes in the staging lanes any cooling effect will have been negated I'm afraid.

2)Inadequate/defective fuel pump.

Regarding the fuel pressure, I've noticed that most regulators, including my Aeromotive 'dead-head', are only rated down to about 5 psi. I'm afraid if I try to set it lower it will affect the fuel flow. I usually run it around 5.5-6 psi to stay within the range of the regulator, but you're right a Q-Jet will run just fine with a consistent 3.5 psi.

I emailed the guys at Quick Fuel Technologies about their 204 gph piston fuel pump that replaces a conventional mechanical. They said it works fine with a 'dead-head' regulator and can supply steady volume at anywhere from 4-60 psi. Sounds like a pretty sweet pump, though expensive.

The only clean pass the car made was after being trailered to the track.
Same sticky track surface same hard launch etc.etc. It would be almost impossible to duplicate the conditions at the track out on the road,think about it, drive the car to the track then park get things ready wait for your call crank it up get in line shut it off and wait, then crank it up move forward two or three spots shut it off and wait, or crank it up and creep along keeping it running and steady watching the temp gauge rise all the while sitting on a black asphalt parking lot with a surface temp of well over a hundred if its in direct sunlight.
Check the fuel lines in the area around the tailpipes just pass the rear axle.

That's right, my only clean passes were when I trailered the car. It was also Febuary, and I only ran the car long enough to open the t-stat before I got in the staging lanes.

Well you're getting alot of good suggestions and advice on what could be causing the gremlin, but nobody has mentioned checking your fuel filters as of yet. I had a similar problem with carb fuel starvation after a hard launch. My problem was debris and sediment in one or both of my fuel filters. When the car launched hard, debris would be pulled by gravity to the back of the filter and restrict flow enough to starve the engine in the higher RPM's, but if i didn't launch hard, it would rev right up to 6200 with no problems. I changed both fuel filters and my problem went away. Just another suggestion. Also, if memory serves me right, don't Qjets have a filter right in the fuel inlet of the carb.

Good luck with your gremlin hunt.

I do have an inlet filter in my Q-Jet. The filter itself has been modifed to removed the little 'valve' setup in it, the fuel just flows straight through it. It's also brand new. I've removed it at the track before and it made no difference at all in the performance. I know it could only help to do an inline filter, but I don't think the filter itself is causing my problems.

Just to add, here's a reply I got regarding the piston style pump I mentioned earlier, from the manufacturer:

"Brian:
Understand the problem. Getting enough fuel to a QudraJet is a pretty difficult situation. One of our employees has a big block Super Stock car and it is always a constant battle and a delicate balance between pressure and volume.

I think you are on the right track to keep the operating pressure fairly low and find a fuel pump combination that can deliver enough volume to keep the bowl full.

Interestingly enough most fuel pumps max flow is actually at a lower pressure, but it is not enough to overcome "G" forces and the fuel tends to stall in the line.

The piston pump actually generates a pretty substantial vacuum on the inlet side, and according to the testing I've seen, upwards of 60 inches which is more than enough to keep the fuel flowing even during the most sever acceleration. Just make sure the regulator you use is a high flow type since you'll only be using one outlet to the carburetor.

Let me know if you have any more questions and if you decide to go this route by all means keep us posted on the results.

Marty
QFT
"

ahem... did he say something about the fuel stalling in the line. I thought he said something about fuel stalling in the line. Somebody else mentioned fuel stalling in the line... oh yeah it was me. LOL Just get your car fixed and go buy yourself a nice dinner, you deserve it for the aggrivation of worring with the car.

lol

60" of vacuum on the suction side of the pump? What kind of fluid were they pumping and where were they testing? The vapor pressure of gas is about 7-8# absolute, so if you lower the pressure in the suction line lower than that you'll have vapor problems. Once you have vapor, you've got to get rid of it before you can get the fluid flowing again.

60" of vacuum on the suction side of the pump? What kind of fluid were they pumping and where were they testing? The vapor pressure of gas is about 7-8# absolute, so if you lower the pressure in the suction line lower than that you'll have vapor problems. Once you have vapor, you've got to get rid of it before you can get the fluid flowing again.

I don't know exactly what the circumstances of that measurement were, or where they measured it, that's just what he told me...

BRIAN,YOUR CAR IS FAST BUT A 12 SECOND CAR LIKE YOURS DOESN'T GENERALLY EXPERIENCE THE HARD LAUNCHES LIKE 10 SECOND OR FATSER CAR DOES.(OPPS CAPS) where you are much more liable to have a fuel delivery issue due to a hard launch then your car would running mid 12's.

If it was a feul delivery issue due to a mechanical issue it would happen weather the motor was cold or hot but yours does not have any problem with a cool off the trailer motor launching hard from the line,its only when the car is driven to the track getting heated soaked under the hood especially in the staging line/s.

As you just confirmed yourself,it ran fine off the trailer & down the 1/4 in cool weather when you didnt drive it to the track,thats a key piece of evidence that driving the car to the track in hotter weather is an issue not to metion the heat soak after the drive whle waiting in the staging lines.

Why don't you just try pouring some cool water over the f/pump/fuel lines/and intake just prior to burnout and running the 1/4,that will put the heat issue to rest once and for all.

Its very easy to do and cost a thing to try so why not try it out before spending any more money and time.

If you try this cooling off thing and it doesnt work then there are plenty of good suggestions by many people for you to try and very likely one of or a combination of these things will get you squared away.

You have already covered most of the bases trying to get to the bottom of this issue with the exception of trying to cool things off with ice water just prior to running the 1/4 so go for it & it just might do the trick.

Scott

Well, this past thursday I did try wrapping the intake/carb/regulator area with a towel soaked in ice water, before getting in the staging lanes. But I had to sit for 10 minutes in the staging lanes after that :(.

I'll definitely try something like that again first, it's cheaper than buying a new fuel pump. It may be a week or so before I can get back to the track though, unless I can try an reproduce the problem on the street somehow. I'll report back after i get to experiment with it.

If heat is indeed the culprit, maybe I can rig up some kind of can inline with the fuel system with a coil of 1/2" fuel line in it, that I can fill with ice water.

Brian,great,glad to see your going to try to cool things off next time at the track to put this heat thing to rest once and for all so you can determine which way to turn next to correct the problem.

Along with the ice on the intake/fuel reg/carb area as you already mentioned you had done in the past do that again to cool the upper end of the fuel system. Then also try pouring some ice water over the fuel pump and over the fuel line/s that come up from the pump to the carb that are either hehind,in front of, or close to the water pump.

And lastly dont forget to at the same time pour some ice water over the f/pump & fuel lines where they come through the frame on the pass side of car close to the ex/headers too.

Just a wild thought,does your fuel line from the tanlk to fuel pump run anywhere close to one of your tailpipes picking up heat there too?

Please get back to us after you try to cool off all of your fuel system lines/plumbing lines under the hood just prior to running the 1/4,i am real curious to see if that helps you out.

If it doesnt the next thing i would do is replace the fuel filter,f/pump & install the lighter pump rod and go from there.

Lastly,i had seen in you earlier post that you were thinking of possibly droppoing the fuel psi down to 4 by tweaqking your fuel regulator? I would try to have at least 5.5-6 psi with your motor that's fairly stout but not much over 6 psi with the q-jet.

4-5psi is too low IMHO with your setup for consistant runs especially on the top end/@ higher rpm's like 6,500 which you told me your motor turns with the q-jet.

Scott

I stated that I was afraid to turn my regulator down to 4 psi, because it was only rated to 5 psi. I do usually run around 5.5-6.

I thought about header/exhaust pipe heat as well. My fuel line only gets within 6" of an exhaust pipe in a couple of places, and only for maybe a couple inches length of fuel line. Nowhere does it get closer than maybe 3". In those 'close' spots I covered the metal line in heater hose and zip-tied it.

Brian,it look like you have already put a lot of good thought into what your problems may be and have checked & done many sencable things to correct it.

I hope by trying to cool off the entire fuel system under the hood next time your at the track pays off so you know whats wrong and where to go next to correct it.

Keep up the good work and i will be very curious to see what happen's at the track.

Dont get too frustrated because between your motor experience and all the experienced people here in T/C you will eventually get this corrected,i am sure of that so hang in there.

Hey,at least the motor seems to run ok on the street so some pesky 5.0 stang doesnt get by you if the motor fell on it's face when you were getting on it,that would SUCK!!!!.

Scott

Remove the filter from inside the carb. It will alow for more fuel to be held inside the carb.

Can you really say the car does not have problems when trailored based on one trip you trailored it to the track? What are the chances if you trailored the car to the track now, you will have the same problems you have when you drive it? One trip in cool Feb. weather is not a very good measuring stick to say it does not have problems when trailored.

Fuel slosh in the gas tank. Fill up the gas tank.

I've had the same problem as you several times

Any A-body with a stock gas tank that I've raced had problems once the car started hooking up hard enough to go faster than high 12's. I bet it would be even more pronounced with a Q-Jet with the small fuel bowl and may occur sooner.

The cure each time for me was to NEVER RUN THE CAR AT THE TRACK WITH LESS THAN 1/2 TANK of fuel.

Filling up the tank would be easier to try than anything else.

Randy

Too late,he has already tried over 1/2 tank of fuel long time ago and it still does it so thats not the issue.

Read all the posts to see what his problem really is and the many things he has already done in an attempt to fix it which may give you some new ideas for him to try.

Scott

Brian,one more thought,if trying to cool things off doesnt work what about the inline pressure regulator.

You have mentioned in the past that you have had issues with it working properly and thought it was not a quality unit. Maybe the spring in it thats part of the assembly that works to adj the fuel pressure looses spring pressure when heated up affecting/lowering the fuel pressure or maybe it just plain sticks or doesnt work properly when the unit in general gets hot.

So with that said if the cooling test doesnt fix the problem maybe you could try bypassing the regulator and running it at the track if the additional fuel pressure doesnt overload/flood the q-jet and it still runs ok with out the regulator.

But because the motor runs fine on the street i doubt the regualtor is the issue but you never know maybe the additional heat after heat soaking in the
staging lanes affects it and the fuel system is not at a partial vapor lock. Time will tell on that one after the testing you will be doing next time at the track.

Scott

I think it's heat related... vapor lock. This is on the 12.80 car in your sig right ? Used to happen to me.

Brian,one more thought,if trying to cool things off doesnt work what about the inline pressure regulator.

You have mentioned in the past that you have had issues with it working properly and thought it was not a quality unit. Maybe the spring in it thats part of the assembly that works to adj the fuel pressure looses spring pressure when heated up affecting/lowering the fuel pressure or maybe it just plain sticks or doesnt work properly when the unit in general gets hot.

So with that said if the cooling test doesnt fix the problem maybe you could try bypassing the regulator and running it at the track if the additional fuel pressure doesnt overload/flood the q-jet and it still runs ok with out the regulator.

But because the motor runs fine on the street i doubt the regualtor is the issue but you never know maybe the additional heat after heat soaking in the
staging lanes affects it and the fuel system is not at a partial vapor lock. Time will tell on that one after the testing you will be doing next time at the track.

Scott

Yeah, that was the $25 Holley regulator I had on there originally. I've already replaced it with a nice Aeromotive regulator, it didn't make a difference. I have thought about trying to run it with no regulator though just to see what happens.
chevellerob, yeah it's the car in my sig. It's not like this is a 10 second race car or something, it's just a street car with a stout 350.

If the local 1/8th mile track is having TNT this weekend, I'll try to make it back to try some of the suggestions out. The 1/4 mile track is too far to drive without knowing if I'll even get in a clean pass.

Old school, definitely eliminates the heat past the pump. If cooling the charge down under the hood will do any good at all, this is the permanent solution you asked about.
http://www.jegs.com/webapp/wcs/stores/servlet/CategoryDisplay?lang=-1&catalogId=10002&storeId=10001&categoryId=14223

Since you've got the 3" of 3/8" line anyway, you've already got the pressure drop so except for the minimal friction difference of flowing through a few more inches of 3/8" line there is no added restriction.

Try installing a cool can

Brian,
Is your gas tank cap the VENTED type? Do you hear a vacuum sound when removing the cap?

I think it's vented, yeah. I've never noticed that it had vacuum behind it when I've removed it.

All the 69 396ss's i have seen including mine had non vented fuel tank caps but i am not sure if the SBC powered 69's are the same.

my cap isn't stock anyway, i bought it at Advanced Auto. I'd have to check it again to see if it's vented or not, it may not be. I know the tank itself is vented with 2 tubes at the top right hand corner.

I know the tank itself is vented with 2 tubes at the top right hand corner.

So is mine, also a 69. I don't think a vented cap is required, but I could be wrong.

If the tank has two tubes, the cap doesn't need to be vented.
The point I was making was to be sure the tank IS vented somehow. :cool:

You ever had the tank out of your car? If not, you might want to make sure the sock isn't gummed up and your vent tubes are clear.

Lots of good suggestions ... I doubt I can offer any new advice, besides what's been given.

I did want to comment on something ... and that is to not bother with carburator issues to resolve this. If your gauge is showing 0psi on launch, I know your Q'Jet will not work without some fuel pressure. So anyhow ... your solution I can tell you will not be anything after your pressure gauge.

Thanks, Neal

Ha, since I'm a bettin' man, especially here at the shop between 9:30 and 4:00 on workdays, I'm still betting idonnow gets the dinner certificate for sure. Too much line. Rig a Mallory above the tank at the frame and push the fuel. Or swap back to stock 3/8".

I hope he finds the prob. soon because mine was acting similar, but I don't think the car is leaving hard enough to stall the fuel in the bigger line.

I just bought some hot water insulating 'tape' at home depot, it's foam stuff with an aluminum backing, and wrapped any naked fuel line under the car, plus wrapped exposed aluminum tubing and fittings under the hood. That should provide better insulation than the heater hose sections I was using before.

I'm going to try and get to the track in the next few days and try cooling the pump and regulator with ice water before a run. That should determine if it's heat or not, and I feel like that is probably the problem. I'll post up results.
At best my car cuts 1.8 60' times, I dunno about the whole fuel stalling in the line thing. Maybe if I was cutting 1.4's or something... A faulty fuel pump seems like another plausible issue tho...

I will hold to my steak dinner promise, when this is all resolved I'll determine who the 'winner' was :)

Brian,

let me know when you are going to the track. I live about a hour away, just outside Winston Salem and I would be happy to go and help all I can.

Bill

i run 110.87 at the track on a street tire spinngin it to 7200 with a 3/8" fuel line, stock pickup and a Holley non regulated mechanical fuel pump, stock pickup with a "4777" dbl pumper holley and have no problems

well, if it wasn't for bad luck I'd have none at all.

I started out for the track tonight, got about 20 miles from home, and had a freak breakdown. Somehow one of the bolts mounting my right rear brake caliper sheared off as I was stopping at a stop sign. The caliper rotated away from the rotor and contacted the inside of my wheel, making an awful noise. It also got in a bind somehow and locked the wheel.
$80 tow charge later, the car is back in the garage without having completed a pass, yet again. :(

Brian,look at the bright side better it happend on the way to the track then at the top end of a12 sec run at over 100pph when the rear wheel could have locked and spun you out of control and totaled the car and you too.

I am glad it happen before you got to the track and that you and the car are safe and that's what matters.

A manit guy i work with just died yesterday because the 1971 chevy impalla convert he was driving went of control on a dry sunny day for some unknown reason and went off the road & slammed into a tree with his 13 yr old son in the car and nobody knows what really happened.

He was 43 yrs old and died instantly from massive head injuries and his son was banged up too but he will recover physically but likely never fully recover mentally from watching hid dad die next to him,man thats a real sad situation for his wife,kids,and family in general.

He used to have 69 396 in high school and just this past yr bought the 71 impalla convert to get back into the fun car hobby again and he was so proud of his new classic ride.

I am wondering if will it come out later he was just going too fast into a corner or something let go in the front end or rear suspension causing the car to suddenly lurch & spin out of controll sending him off the road into the tree.

Be glad you and that nice quick 69 of yours made it home safely when it could have been a very different outcome if it happened at the end of a 100 mph + 1/4 mile run.

Dont forget to check the other rear wheel caliper on the other side to see if the bolt is loosening up or breaking like the other one just did to avoid a possible accident. Even if it's tight i would still locktite (med strg Blue should be good enough) the broken bolt your replacing and all the other bolts that hold the rear calipers on just to be safe.

Also take a min just to check/ensure the rear ujoint nuts and pinion nut are tight while your back there too since your doing a lot of racing just to be safe. If any of those are loose use red locktight to keep then tight. Chk the upper & lower rear control arm bolts too.

Scott

I emailed the guys at Quick Fuel Technologies about their 204 gph piston fuel pump that replaces a conventional mechanical. They said it works fine with a 'dead-head' regulator and can supply steady volume at anywhere from 4-60 psi. Sounds like a pretty sweet pump, though expensive.

Got one. You're right. Sweet. Alky or Gas. Carbs or Injected. For everything else, there's Mastercard.

Scott, you got that right! I'm glad it happened before I got to the track. Now I need to repair this and check over all my suspension/brake bolts, then back to the fuel pressure stuff.

It was dissappointing, it was such a nice cool night out, and the car was running great on the way out there. That's how it goes though.

Brian, I was just looking at your home page. Your car is awesome !! Great work. I look forward to seeing your car..... oh yeah, and meeting you too !!LOL

Bill

Lots of good stuff so far.

I agree with a few others that the fuel is vaporizing in the suction side of the line. I don't think you're having any problems on the discharge side of the pump.

The vapor will accumulate in a high point in the line. If you have an area where the line loops up and over something, the vapor could be accumulating there. If you have such a high spot, it is possible, although not likely, that the vapor is air that has never been removed since you installed the line.

This problem with smaller diameter fuel lines will not be as severe or noticible. The velocity of flow in the smaller lines is much greater. The higher velocity does a better job of moving the air bubbles along.

Since the larger line holds more fuel, the fuel is in the line for a longer time. Thus, more time is available to heat the fuel until it vaporizes.

Don't be surprised if the insulation you installed does not solve the problem. It will only slow the rate of heat transfer. The problem could be worsened if the insulation holds the heat in and does not allow the fuel line to cool, and the vapor to return into solution.

I would guess the problem manifests itself at the track because you are launching much harder than on the street. The G-forces at launch try to push the fuel in the line back to the tank. This reduces the suction pressure at the pump. If the suction pressure is reduced to the vapor pressure of the fuel, you have vapor lock. This problem is worsened with smaller fuel line. With smaller line, the flow velocity is higher and the friction between the flowing fluid and the walls of the fuel line is higher. The friction causes increased pressure loss, and further reduces the pressure at the suction side of the pump, increasing the possibility of vapor lock.

As already stated, it is almost certain an electric pump mounted at the tank would resolve your problem. 3/8" fuel line would probably do the trick as well. If you really want to keep the mechanical pump and 1/2" line, a return line to the tank may be the ticket. It would increase the flow velocity and reduce the fuel temperature in the 1/2" line.

Pesky double post

The vapor will accumulate in a high point in the line. If you have an area where the line loops up and over something, the vapor could be accumulating there. If you have such a high spot, it is possible, although not likely, that the vapor is air that has never been removed since you installed the line.


You might have hit on something here, I have a bit of an awkward 'loop' from the hard line where it comes through the frame under the A-Arms, to the pump inlet. The loop isn't horizontal, it goes up and back down. Maybe that's aggravating the issue.