Okay, I've had this problem in the past but it's never slowed me down this much...for what is usually a 14.00 car, this is just rediculous. I pull up the to bleachbox in my '66 GTO, do a three speed burnout, and the car pulls rediculously strong through all speeds and rpms. Then I stage and launch. When the car gets to about 3500 rpm in 1st, the engine just lays down...the rpms fall, and I can feel heavy decelleration - almost like compression braking. The gas gauge goes almost all the way to the left (empty) even with 3/4 of a tank. as soon as I let off and the car stops accellerating and the gas gauge goes back up, the engine picks up again, and off I go, full power through all gears and rpms. I'm running a mechanical pump (holley race) a high flow filter (about the size of a pop can) a two row fuel cooler and a pressure regulator. The pickup in the tank is stock. Any ideas? Think this might be the solution?

http://www.holley.com/HiOctn/ProdLine/Products/FMS/FMSFP/12-951.html

Sounds like an electrical problem to me,sounds like you lost ignition,with fuel guage dropping makes me think that.

EDIT: A friend of mine chased the electrical gremlins for a year,he could do his burnout,launch then pop,crack,spit,sputter then try and take off,his battery is in the trunk and his main battery cable had rubbed a hole in the insulation and was shorting on the frame while trying to accelerate. It cost him a fortune in ignition and fuel system parts before he found the culprit.

How 'bout some sort of fuel tank venting problem?

sounds like your running out of gas. fill the tank to the top then try it. if that fixes the problum then you need a new tank. order one with a baffel in it. it will; gelp keep the fuel from running to the back of the tank and away from the pick up.

Instead of ordering a new tank with a baffle, why not order a baffled sump and have it welded to your old tank?

Sounds like you have a fuel delivery problem.

I'd bet your fuel pickup, aka sending unit, is plugged up with the 35-year crusties. All the high-volume pumps and filters and coolers in the world won't do a bit of good when all the gas has to get sucked through a tube that's built up to within a toothpick's diameter with dried fuel gunk. That's what always happens, especially if the car has sat around alot (years at a time especially) without being driven.

Before spending any money though, verify that this is what's happening. Easiest way I know is to do a full-power run up an expresway ramp or something; then when the car does it, IMMEDIATELY turn it off (OFF, not LOCK, although you may not have Lock in a 66) and pull over to the side, WITHOUT LETTING IT IDLE. Then pull a fuel bowl and see how much gas is in it. You have to cut it clean, out of gear and the ignition off, so the system doesn't get the chance to refill it under no-load (low demand) conditions.

I'm betting if you do that, you'll find the fuel bowls dry.

The gas gauge goes almost all the way to the left (empty) even with 3/4 of a tank. as soon as I let off and the car stops accellerating and the gas gauge goes back up, the engine picks up again, and off I go, full power through all gears and rpms.


If it was fuel,how could he go back to full power thru all gears :confused: The first part of the track is where all the reaction,traction is taking place, I'm still thinking electrical short somewhere.

depending on the use of the car . if you are only driving it on the street and the track some times but want the factory look get a baffled tank. if you dont mind the race car look get it sumped. i did both. it dosnt sound like eletrical to me. also cheak your float level. it could real low

a 14 second car doesnt need a sumped tank.

If you didnt change anything, everything was working fine before hand, then a current part is broke, and simply needs to be repaired or replaced. With no changes, you're full system isnt going to become inadequate out of the blue.

Go over all your major grounds, go over your electrical system with a fine tooth comb looking for a wire that rubbed through the insulation, or something shorting out on something else.

If you still cant find it, i would start going through the fuel system looking for something thats out of whack, looking for a hose that could have been cut when it was put together, making a flap that closes up under pressure sometimes.


The best advice i can give you, is Dont throw money at it, find the problem before you decide to repair or replace it.

Hey swingkid, this didnt happen to have happened at pacific raceways on friday for the high school drags did it? graemlins/beers.gif

yeah! it did! That was me in the blue '66 at the high school drags. ugh! I came in 4th last year! This sucks! but as I said...this is a problem i've been chasing for a long time...but I haven't experienced it in a while...I thought it was fixed after I installed the new pickup, fuel cooler, filter and regulator. I have to think it's fuel, because it only happens under hard accelleration AFTER a burn out... when I floor it from a traffic light, there's no problem. So if the bowls ARE dry after I come up hard on the freeway on ramp...how do I fix that? It seems like baffles in the tank or a sump would be the answer...but thousands of people have run their a-bodys well into the low 13's...12's even without doing a thing to their fuel tanks... thoughts on the holley part link above?

I'm running stock tank,stock pickup,stock sock for all I know,stock fuel line,Comp 140 pusher,Carter 120gph mechanical with 8an to the carb. Ran 12.10,12.14,12.12,12.30 yesterday. Maybe it was a bad case of vaporlock?

some factory tanks have the baffle and some dont .

Look for an electrical problem.

I second that it would be a venting problem, does your tank have only one hard line coming out of the top, or 2 like my chevelle's does? Venting gas cap maybe? I know that your fuel system is definately up to the task, you've got it set up pretty nice, only thing would be maybe your regulator is faulty...Do you happen to have a fuel gauge inside the car? If not then maybe you could see the pressure dropping off under load.

If its electrical, which it could also be because of the gas gauge dropping off, I would say make sure you have good grounds from the engine to the firewall, ass well as any other places that may be needed. Hopefully you can get this problem fixed quick. graemlins/beers.gif

P.s I was the guy who offered you the timing light and tools incase you needed them at the drags on friday, my friend drove the teal 70 ss nova. When do you plan on going to the track again with the free pass? My friend will be there this wednesday, but I live in bremerton and wont be able to make it.

It's not baffles; it's a buildup of dried-out gas gunk that's accumulated over the years. It wouldn't surprise me if you couldn't even get a coat hanger through your pickup tube the first time you try.... that's how bad they usually get.

Just take your sending unit out and look at it. You probably won't believe your eyes.

I recently replaced my stock 5/16" pickup with a factory 3/8"

When i pulled out the stock one, expecting to see a bunch of crud....to my surprise there was nothing crudded up on it, at all.

I know that its the original sender from 67'.

I'd bet that they only crud up if the tank is all rusty.

I had the same problem when I had a Qjet the top gasket in the carb was blown out causing all the vacuum and fuel metering problems I ran a 20.8 @ 51 I believe. :D

but I put a new sender in two years ago...could it really build up that fast?

I think you have an electrical problem

Well, since you told me that you drive your car pretty regularly, I dont think that your sending unit is plugged up. And i think the only way to see if it is a fuel problem is to get an in car fuel gauge that is set up right before entering the carb. I personally dont think it has anything to do with a baffle or sending unit (since yours is new), I think if it were the tank it would be because it is not properly venting. Maybe it has something to do with the floats, like they are stayin open after the burnout, then closing once it has surged for a while...who knows, it could be a combination of a thousand different causes.

I would look for an electrical wire that could be pinched on hard acceleration. The motor may torque over enough that when you hook hard it pinches an electrical wire. I would check for any possible pinch places back to the fuel pump.

Sorry, forget the fuel pump idea, I forgot it was a mechanical pump.

Oh, I discovered that the fuel psi was down around 3 on the regulator when I ran the race. Obviously, that is way to low. The nut on the regulator must have come loose. My Q-jet book says 7-8psi, but I have also heard "no higher than 6" What psi do you all reccommend? The q-jet is pretty well built (oversized needle and seat, no internal fuel filter, no fuel baffle (the round plastic thing), lots of other mods done at JET Performance) So I plan on rebuilding the carb today...maybe I'll toss that baffle back in the carb with the new gaskets...

Cool, how did you find out that the psi was down when racing? I would think that 7 PSId not be too much, I say shoot for 6-7 PSI throughout the whole run. I was almost sure that it was a regulator problem, because I know of a lot of cars that go much faster on the stock tank and pickup, and not all have the nice fuel system like you do. Hopefully if you can get the pressure back up and constant, it will solve the problem, Good luck graemlins/beers.gif

Would this by any chance be the Holley 12-835 pump or something of the same design for your application? I've had 3 of them fail in 1600 miles. They don't die altogether but they lose their ability to keep up. Everytime one failed I could look at the little liquid filled pressure gauge I have on the feed line for the carb and rev the motor up to about 3000 rpm and they pressure would just slowly drop to almost nothing. I now run the Carter 172. :D If you've got the Holley mechanical I would recommend you check it....

Thanks for the tip! Actually, thinking back, I believe the problems started happening shortly after I had replaced the fuel pump. There were so many things going on at once, I couldn't find the culprit! The hottest mechanical pump I can find for my engine is the carter 120gph at 6psi. Think that'd be enough? I've got the old Carter I removed from the engine (it wasn't "Broke" but I fixed it anyway) the p/n is 0-193 or 0-195 the numbers are rubbed off. the other side is stamped with "5074k17a" I might just toss the old carter back on and see what happens...thanks again for the help everybody! I'll keep you posted!

This is where I got my Carter. Carter 172 (http://www.sdpc2000.com/cart.asp?action=prod_detail&catid=3215&pid=29708) They don't have anything listed for your application but you might call them and maybe it's just a case of them not having it on the website?

Lance

GLAD YOU FOUND THE PROBLUM

I had a similar problem years ago with the El Camino, found the main power wire terminal in the firewall feedthrough to the fuse block crudded up, not making good contact. Put a heavy ignition load on it while making a run, and it would die. Take a look at it, you might be surprised. Any older car needs to be checked IMO after 30 years or more of constant use. I cleaned the terminals up with some sandpaper (220 grit or so), bent them back towards each other for more contact pressure, and never had a problem again.

How are people coming up with fuel delivery as the problem? If the car can do burn outs (run the HELL out of low gears) there is no fuel delivery problem. The feul gauge drops off to the nothing, then comes back when you back off the throttle...stock fuel level guage, right (electrically operated)....(decelleration = change in direction to oppsoite direction = direction in which electrical circuits that needed to be closed were closed as proven during burnout) You weren't talking about a fuel pressure guage, right? Granted I haven't looked at the car, but I am a mechanic and strongly suggest you start chasing wires. It sounds to me that a harness, or maybe even a single wire is shifting position under acceleration, breaking a circuit. Chances are everything is properly grounded. I would start chasing the hot leads right off the positive side of the battery terminal, and expand your search from there. I don't have a wiring diagram in front of me, but I'd be willing to bet it's a single chafed hot lead grounding out due to a shift in position caused by the forces of acceleration.

Make sure the firewall plug isn't causing the whole mess. You would not believe the things I have seen go wacky because of the firewall plug being loose or dirty.

I had this EXACT problem with a 76 Trans Am. My mechanic friend had me replacing modules, various ignition components, fuel filters, etc. I kept the mechanical pump, but added a Holley red street pump to use when needed. It solved the problem. I know it solved the problem because it could be replicated when the pump was off. Full power passes when the pump was on.

well as of right now if you read the whole post you would see it looks like a bad fuel pump. thats how us guys came up with fuel.he posted that its falling on its face. dont think he sead any thing about shuting off or braking up. if he did we would have been looking for eletrical.also by saying that it happons when launching the car that would tell me the fuel is not getting to the fuel pump.the car runs off the fuel in the bowls untill 3500 rpm then the fuel pump cant keep up the demand.one of 3 reasons.
1 no baffel in tank to stop fuel from running away from pick up
2 cracked fuel line stoping pump from sucking the fuel.
3 bad fuel pump.
that is how i belive that some of us came up with that. so how do you come up with eletrical?

i dont see why it needs baffles unless he's running real low on fuel, or pulling wheelstands ;)

maybe im using the wrong word . how about bulkhead. some stock tanks are empty in side and some have a devider. the devider helps to hold the fuel around the pick up. i had a tank out of a 71 chevelle in my 72. i couldnt run into the 13's with out the car falling on its face. i spent hundresa of dollors trying to fix the problum. eletric fuel pump ,holly macanical fuel pump, even tryed both inline. new pick up ,rebiult carb , new msd, changed coil , i could not find the problum. i got alot of help from chevelles.com. butno one ever told me about the tank. well i went out got a new tank with the baffle/bulkhead in it and it fixed the problum. nnow i have a sumped tank. becuse if your running an eletric pump. then you want the pump to be gravity feed. i hope you under stand a little better if not then i dont know how to explan it other then the force of the fuel moving to the back of the car takes away from the force of the fuel pump trying to pull it. basicly its a tugowar in your tank

I've seen too much to prove otherwise. You're fuel starvation problems could have been caused by the way you routed your lines, the fittings you used. ect.

If it works for you, Fantastic, but dont insult me becuase i prefer to use the KISS method.

well i hate to say your wrong. i simply state that this could be a problum. for this person and i stated a way to cheak if it was the problum.but for some reason you feel to under stand the basics of how the fuel systum works graemlins/clonk.gif .thir is no reason for you to get on me becuse i tell someone to cheak some thing. i didnot say to go out and have a tank sumped or spend money where it isnt needed. i simply gave info in things to elimanate. im glad you never had this problum but if it was never a problum. pepole wouldnt sump their fuel tanks in the first place!!!

If you are so convinced feel free to come out to Englishtown on Sunday May 30th, prepair to be amazed!

You'll find out why i dont believe a 14 second, or even a 10 second gas powered car needs a sump, 1/2" line, or 250 pump.

But i'm not going to argue over it, or take your insults!

glad you found the problem... i was gonna tell you to work on your 60'... ;)

Originally posted by Motor Martyr:
If you are so convinced feel free to come out to Englishtown on Sunday May 30th, prepair to be amazed!

You'll find out why i dont believe a 14 second, or even a 10 second gas powered car needs a sump, 1/2" line, or 250 pump.

But i'm not going to argue over it, or take your insults! i dont see where any one insalted you. but if i did my mistake. but i still feel your wrong on nonbaffled tanks not being a problum in older cars. end of debate.