I wasn't sure to stick this here or in troubleshooting, but here it goes..

I looked over my exhaust for any obvious leaks-- header flanges not tight, collector gaskets, loose clamps, holes in welds, etc. Nothing.
The exhaust my car makes stings/burns my eyes wicked (edit: very, for those not from around here) bad. This indicates a very rich condition right?
I have heard a few people before say it was lean (not on this board, in person, that made it burn your eyes), but I thought it was rich. ??
Second, and I wasn't around in the 50-60-70's to deal with carbs and all that fun stuff. Is there something up that lets the exhaust smell get back to my eyes and permeate my clothes?
I don't have turn downs, I have full tailpipes, they exit straight out the back (one of them is a little too high and hits that painted panel below the bumper on 70s and stains it, but thats about it). I can't think of anything obvious.
Is that how it is for all of you, and I am just used to modern technology?
I am considering an AF meter because the cam swap guy welded a bung in there for me (he filled the hole, just said I need to drill it out and screw in the sensor if I get a AF ratio meter one day).

Any thoughts here?
I also wanted to toss out that anyone think this is related to my 1/2 drop in gas mileage after my cam swap? 10 I could deal with, 5/6 is alot harder to deal with. I know I had problems with the smell before, but the burning of the eyes was never as intense.

Thanks everyone..

Matt

not knowing for what you have for cam compression and carb.........i would say maybe since you changed cams your vacuum reading is below you power valve number......that will add more fuel to the idle......as cams go up in size ...over lap gets worse and at idle there is more unburt fuel get past the exhaust valve.......most of this can be tuned out of the carb......in the idle mixture circut messing with air valves and restricting fuel metering paths.......my first guess would be power valve....friend of mine did his huge cam change and what not and he left his stock 6.5 "hg power valve in and at idle he was only pulling 4" and you could stand in the garage for very long before you had to shut the car off and get out........but after he stuck in a 3.5" the car idled better and alittle smoother.....plus the smell wasnt so bad then..........still alittle smell with the 305 comp cam but not bad........

Sorry should have added that info. Carb is a holley 750DP with 850 baseplate, cam is a comp cams solid roller 287/291 @ .020, 256/260 @ .050 .643 lift, 2" hooker super comps, 3" torque tech exhaust/custom x pipe, 72/78 jets, 6.5PV, .120 needle & seat, 10.14:1 CR, 28 HS air bleeds front & back, 59 LS air bleeds front/back, 31 squirters.

Matt

Dude, it's called overlap, and anything near 240+-ish.050" will give it to you. Buy some of that strawberry stuff to make your exhaust smell nice - it's all you can too.

Option two is to not use vaccum advance at idle, use ported. Retarding timing will clean it up some, but at the cost of a ratty idle.

Yeah, I know what you mean, when I back the car into the garage and miss, having to pull up and do it again. Man. Tear gas hut. And my mill burns clean and lean.

You'd think that if it was leaving the tailpipes w/o a leak, I'd be ok, the gas would just annoy people behind me? Guess not.
Today I was driving around with the vacuum advance plugged period, I will give it a shot a plugging the advance to ported vacuum (that is what you mean right?)


Matt

Yes, exactly Matt. I tried it, it cleaned the smell, but my engine just prefers to idle with 23 or so degrees in vs. 17. I chose smell over ratty idle. Plus, if you recall that last mpg thread, those measly 8 degrees are worth around 3 mpg on the highway. ( it's only 6 at idle vaccum btw, no typo).

Not to challenge dennis, but if idle is set correctly the power valve circuit SHOULD NOT be flowing fuel at idle. On 4 bbls, this typically requires cracking open the secondary to where the transfer slot is just peeking out from behind the throttle blade, and I mean you can just see it. This gives the secs some airflow, reducing the airflow through the primary bores. Too much airflow through the primaries at idle will pull fuel through the boosters, typically using the PV channels as its feed.

I had a 68 442 that had a leak at the trunk seal. The exhaust gases would enter the car there. Very unpleasant.

and when does the power valve open in madmarv engine? well the answer is 6.5"hg......at idle i would lay money down and say his vacuum reading is closer to 4 or 5 " of hg.......meaning he IS dumping raw fuel into the motor at idle........the power valve is an enrichment circut for when the vacuum reading falls below the designed number which in this case is 6.5" hg and if your sitting at idle with 5" of vacuum where do you think the extra fuel is going.............this carb needs a 3.5 power valve .......this will help clean up the idle as well as help reduce the smell from the pipes...........retarding the timming does not help one bit with the smell.......the best thing to do is get your 20 some degrees of intial timming and put a factory 10 degree vacuum canister on the hei and hook it up to full ported vacuum..........this will make the engine run way cooler and reduce the unburt fuel smell, help increase the gas mileage and it will also allow you to turn the carbs throttle plates down even farther and make the idle mixture screws even more responsive and you can lean it out even more to farther reduce the smell of the exhaust...........fine tunning plays hand in hand and if you do everything right your smell wont be an issue.......granted you cant get it all gone but it wont be an issue no more.........

right now you dealing with a open power valve........change it to a 3.5 and buy you a 10 degree stock canister and use it in your hei and hook it up to full vacuum (this is the best place to hook it up ...when you mash the gas pedel the extra timming falls away and just goes back on the mechanical advance) your engine will run cooler and your idle will be more stable.....and you can lean your idle mixture screws out alittle more to help with the smell..........

Unless the PV is ruptured raw fuel isn't dumping into the engine. The PV feeds the fuel wells just like the jets do. A ruptured PV could be the problem.

QUESTION I have a camshaft with a long duration and a high lift. It will burn your eyes at a idle. What can I do to fix this?

ANSWER The most common cause is an improperly rated power valve. You will first need to choose the correct power valve for your application. This is covered in another section of the Technical Information Library. When you have a camshaft of this configuration it requires more air and fuel for it to operate efficiently. This in turn requires you to raise your curb idle screw to obtain the same given rpm that you had with a stock camshaft. If you are having a problem with the air/fuel mixture screws not making a difference then what happens is with turning the curb idle screw in farther this will sometimes cause the throttle plates to open too far and they will uncover the idle slots. This will allow it to bypass the idle circuit and start pulling fuel from the transfer slot. To correct this problem you can raise the secondary throttle plates a little with the secondary adjusting screw allowing more airflow into the engine. This will allow you to lower the primary throttle plates so you will be able to get back into the idle circuit. Another method would be to drill a 1/64" - 1/8" hole in each of the primary throttle plates on the side closest to the transfer slot. This will allow extra airflow into the carburetor also alowing you lower the primary throttle plates.


STRAIGHT FROM HOLLEY...........

Ok. Thanks for the help so far guys.

I decided to go out and do a little test because I hadn't actually bothered to write this info down. Spare me execution if I screw some of the terms up (I'd rather a mass air meter and a laptop).

When I connected the vacuum gauge to the manifold directly, I registered 10" in park, and 5" in drive, at full temp, electric fan on.
When I connected it to where I usually connect the vacuum advance on the carb, I registered 7-7.5" (this vacuum gauge flutters like nothing else in the world, well, my oil pressure gauge) in park, and 3-4 in drive.
Now for the embarrasing part, when I taped the gauge to my windshield and took a ride up and down the road, the vacuum was always near 10" at cruise, higher at non cruise. I am using gas at levels that are IMHO unexplainable unless I am dumping raw fuel. I wish I had an AF (lambda) whatever you call it meter to see for sure here before I go and change the power valve.
The question is, I don't spend most of my time at idle, so is there some separate issue with the smell getting back into the car? you would think with tailpipes going 35mph the stuff would just blow away. I suppose the burn your eyes is at idle, and is mostly bothersome after I get out of the car.
ddennis, with this "stock vacuum thing" I am not sure what it is-- but when I do figure it out, you suggest connecting it inbetween my vacuum advance and full manifold vacuum?
But since I don't spend most of my time at idle, and cruise hg is above 6.5, why would I continue to be dumping raw fuel?
(I posted this before I read the holley cut and paste reply and pat kelley's)

Thanks

matt

i have these problems too.

in my 427 is a 305 comp magnum, its 253@.050 and has something like 85 degrees of overlap. ive done all the tricks as far as power valves, transfer slot relationship etc. etc. etc. i went from fouling plugs once a ride to a nice golden tan on the plug.

BUT the exhaust still stinks, not as bad mind you but it still leaves your clothes smelly and burns your eyes when in the garage.

with the size of your cam if your plugs are a nice golden brown i doubt you will be able to make it any better as far as the smell. about the only thing you can do is get some of that additive that Gene suggested.

Well, I was kidding about that stuff, unless they make some real unique smells, i.e., Perry Ellis 360 ( my fav chickie perfume), or the smell of burning hemp to freak out both my pothead and cop friends! ;)

Matt, while I;ve never run a cam that large, I'm not liking your vaccum readings. Flutter is a no go. Steady is where you need to be. Flutter is typically lash being out on a few valves, or, as I'm experiencing now, a marginal wire OR a bad plug ( new AC's?), or something. Your vaccum should be STEADY. Anytime mine flutters, something is amiss. Like now. And to the chagrin of the racers here, my azz dyno doesn't make a mistake. I know something is wrong. Know the car too well.

Can't even begin to guess, although I would probably do the same thing I will when I get time ( yeah right), pull plugs, check cam timing, check lash, test each wire, inspect cap/rotor, replace plugs and it should be gone. Kinda hope I find a wire that's pulling mucho resistance.

Or its the damn 100LL gas which I can't seem to get rid of. Driving this ride easy, gas milage is too good. 85 city/highway miles and it's only down 1/4 tank. Need to drive it more and get the fuel cleaned out and fresh in. Not comfortable rippin' it when I know something is slightly off, whatever it is it isn't effecting milage.

Anyway, something is wrong, and in addition to the very short list above, if the carb isn;t metering right, it will also cause a flutter.

Like Dennis says, throw a 3.5/4.5" PV in there. It's not a correct fix, but its a simple one.

Well, I was kidding about that stuff, unless they make some real unique smells, i.e., Perry Ellis 360 ( my fav chickie perfume), or the smell of burning hemp to freak out both my pothead and cop friends! sounds like you been watchin cheech and chongs up in smoke. ;)

my 427 pulls 14-14.5 inches at an 800-850rpm idle. it does fluctuate a half point, but thats due to the very rumpity idle. i can raise the idle speed up to 1000rpms and the vacuum fluctuation goes away.

My engine is tuned right and I get a pretty good whiff of fuel at idle (enough to set off the smoke alarms in my house). I've tried leaning the mixture ORCH but the engine won't hold a steady idle. I have 85º of overlap and that is why. A lot of fuel is dumping out the exhaust. Just one of the characteristics of a lumpy cam with lots of overlap. You have to run the idle rich to make up for residual exhaust gases in the chambers.

If the PV is ruptured, the engine will be very rich all the time. Changing the PV opening point won't make much difference if the existing PV is good. I ran my engine for several months with a 65 PV even though it makes only 6" at idle in gear. Ran great and the idle was fine. The carb I'm using has the secondary blades opened a bit, holes in all four blades, and a 4 corner idle system. With a lot of overlap, don't expect the vacuum to be rock solid at idle. There is quite a bit of reversion and pumping action going on in the manifold.

Gene,

I am going to be talking to the guy who did my cam tomorrow, I'll ask him about the power valve, and I'll ask him about the converter.
The thing that has got me worried is the flutter. My vacuum readings on the old HR cam used to flutter too.
it is steady under RPM-- like 1500 plus-- but under that, I mean, it can swing from 2-4 or 10-14 it just bounces around like nuts.
Get up to an RPM,and the thing pulls a steady vacuum.
Down low though, in gear or in park, its all over the place.
Do you mean only flutter at 16" is a problem, or is it a problem when its down low?
I can't see how it _could_ be stable down low, the engine RPM fluctuates at idle?

Thanks
I am ordering a lamba/AF meter tomorrow, I figure its a good insurance policy for what it costs, even though I am convinced my carter 172 does its job after Tom Bairds test.

Thanks guys

Matt

How do I test for a ruptured power valve?

At this point I'm not sure where I am going to go here, but I think for me the lambda/AF meter is a good idea to help tune this thing out. The tires and stuff can wait.
I am assuming something is wrong-- we all joke about the gas mileage here, but I seriously drove about 12 miles today and took down about 4 gallons of gas, and I never once WOT'd it, or even close, heck I don't even know if my tranny kickdown works because there are no appropriate areas to test it on around here.

Thanks
Matt

Something is amiss. Check the plugs? Don't wash all the crosshatch off your cylinder walls or else you'll be one unhappy camper.

Matt, when the old 427 is in a proper state of tune THERE IS NO FLUTTER AT ALL ANYWHERE. Even if I drop the idle to 800 and pull 8"

( WITH A 10.5 POWER VALVE BTW!)

Again, the flutter has always told me something is wrong even before I could feel it. It should not flutter at idle. Caveat is, only experience is with my 440 and 'small' cam. Haven't a clue if the same rules apply to beasty cams like yours.

I don't know what if anything is wrong with your engine but I wouldn't worry too much about the flutting vacuum reading unless it is wildly erratic. I would expect to see some needle movement if your cam has alot of duration.

Matt, For what it's worth, I'm running the same cam as you, I'm no carb expert so I had Avanti (http://www.avantiperformance.com/home.html) set it all up for me, it runs great and has a decent idle but IMHO a cam with that much overlap is going to stink at idle and not really clean up until 2000 rpm where it's designed operating range begins. The smell is just part of the fun.

The easiest way to test for a bad PV is to replace it with a good one. If it is seriously ruptured, you can suck on it. If you draw air, it is leaking. They are not expensive. 65's are pretty much readily available. Lower opening points might be harder to find locally. Do not use a 2 stage PV, they are for trucks, RV's, and such, not performance. I suggest getting a book on Holley carbs. A lot of useful info in there. I gather this old technology is new technology to you smile.gif .

What I am seeing in either park or drive, manifold or carb vacuum, is a flutter between two set points, say, for carb vacuum, 2-4 or so in drive, and 6-8 in park. For manifold, 10-14 park, 4-6 in drive. It just sorta rapidly flies between those two points.
I also would like to point out, and maybe this will help someone say 'try this,' is that my "idle" RPM in park is like 1300-1400 when the engine is hot, and 900 or 1000 in drive. Is there any way to get this thing to idle more, well, in tandem? Just playing with the idle screw or the 4 corner idle screws will bring everything down or up- but not closer together. So there must be more to it. I have this red book, like "how to tune your holley," and its far more useless than the breakdown of where the parts are that came with my carb. Or is that just the deal when you get signed up for my cam?
I am assuming that since I lash it at 16 I 18 E, and its rated 287/291 @ .020, its actually more like something like 290/294 (just a wild guess here) where I set the lash. Comp just lists these lobes at .020, the cam card said 16/18, and thats what I was told when I was told how to set it up.
I've checked the valve lash a few times, and you'd expect a big cam to move around, but I guess my stud girdle just says no to moving.
I should make a list of things to talk about with the cam guy tomorrow, aside from just the power valve and converter.

Man-- maybe I'd have more fun with the TBI setup off a wrecked late 80's 454..

Matt

MalibuSS396,

Wanna shoot me an email if your OK with it? (yours isn't listed as far as I can tell) I'd like to ask you some questions if possible.

Thanks

matt

Sometimes simple things like a dribbling accelerator pump will create a lot of headaches. Years ago I had trouble tuning in the idle on a 11-1 350 with a 300 duration cam and the problem was when then engine shook at idle from the choppy cam it would jar the accelerator pump lever just enough to dribble some fuel from the shooter. The fuel would dribble in beat with the engine shake and made the idle very very radical. I adjusted the pump linkage for .010 clearance with the blades closed and the idle became stable. Then I cracked the secondaries just a bit and adjusted the mixture screws. The thing ran like a totally different engine, clean plugs, crisp throttle, etc.
I think if you make sure the timing is close to optimum and the idle circuit is tuned appropriately with no internal carb leaks the thing should run fine. A stall converter may be necessary also. Bob

Matt, forget what I said about idle vaccum, since I can't confirm it works the same way on a big cam mill. Can only say its characteristic of mine. THe only valid point I made above is, check your plugs, if you're dribbling fuel, they'll be black and sooty.

TPI/EFI, naw buddy, source yourself a tripower. I'll set it up for you and guarantee it works "out of the box". Carbs through Holley custom shop. No finicky Vette stuff allowed.

Actually if you want more efficiency, big QJ.

I finally found a shop to do a wheel alignment to global wests specs before I actually ruin my tires, I'll do a plug reading when I come back down the highway, then I'll talk with the cam guy.
462 or not-- I think something is up just based on fuel consumption.

Matt

Hi Matt - I just sent you an e-mail w/ my address. Rich

Gene, I called Holley regarding those carbs a month or so ago. Holley referred me to Specialty Parts Warehouse (770) 270-1116 for the Chevrolet carbs. When I spoke to them they had carbs for '67-69 applications.

I was planning to run a tri power set-up for my 496, but will be re-piping my house instead. BTW, I heard Barry Grant now has tri power set-ups available for big blocks, too. I haven't been able to confirm it yet, though.

Originally posted by 427L88:

TPI/EFI, naw buddy, source yourself a tripower. I'll set it up for you and guarantee it works "out of the box". Carbs through Holley custom shop. No finicky Vette stuff allowed.

Actually if you want more efficiency, big QJ.

so i guess the makers of holley carbs have been wrong all these years including myself........on how to pick the power valve for your engine. holley tells you clearly that your power valve must be 2" of hg below your lowest vacuum reading in gear at idle.......and think about this for those who say the power valve dont do nothing at idle ......while the engine is pulsing between 6-8" of hg the powervalve 6.5 is pumping back and forth acting like a pump.....where does the fuel go to....maybe out the booster.....

holley tell you straight out if the car is burning your eyes it maybe the powervalve............weather its reptured or the wrong size........it has to be corrected before you can go one........

timming is very important if you have a huge swing in the rpm drop from park to drive.......most problems lay in the dist.....using to loose/weak of a spring can cause the motor to have more timming at 1300 rpms and way way less at 900......timming has to hold steady from park to drive.....weather your car idles at 1000 rpms and 800 in drive the timming should not change............everything i have been saying works hand in hand there is not one cure all for you smelly fuel problem........every little aspect of the carb and timming must be acknowleged........and once every little detail has been covered and done then you can enjoy a better smelling exhaust..........it wont be totaly gone but you shouldnt be walking past it saying oh my gosh thats bad.........

I'll check out that timing thing Dennis. Never occured to me to check that.

I'll have to give it a whirl this weekend.

Thanks

matt

I bet the power valve has no effect on the idle, put a powervalve plug in and the idle mixture should be the same-simple way to test the powervalve relation to idle. Now if the powervalve diaphram is ruptured that's a different story, it'll leak gas through the baseplate for sure.

Dennis, like any other engineering application, there's the " commoner advice" and then there's the engineer advice. FOr the common guy who has a hard time setting a carb up, or doesnt intricately know how they work, the PV 2 below idle vaccum is fine. It's simpel advice and works OK.

Ask a carb guy about it, and see what they say. Please don't take my advice.

Wes, no you misunderstood. The carbs from Holley are NOT Vette carbs, they are reman 2300's with 1850-style side hung float bowls attached and the tops milled for the half-moon trips air cleaner. Also had them plug the rear vaccum port ( for P/B I think)and swap out the 500c pump housing for 30cc housings. #31 center squirter, 25-28 on the outboards, PV plugs in ourtboards 78 jets, 10.5 PV in center 72-73 jet and you're done. Total cost was $777 w/ shipping from the Holley custom shop. They did require just a bit of die grinding to fit, but nothing major. All 3 carbs looked nice and fresh with the new dichromate finish.

If I was to order again, the only thing different would be to ask them to remove all the extraneous arms, etc, from the throttle shafts and I **think** I would have used the rear float bowls so that the fuel inlets would have been on the wrong( passenger) side. Would have been much easier to do a fuel rail with all that room on that side vs the throttle side.

So again, in short, they are custom 2300-style carbs using a mechanical progressive linkage. Last I checked trips carbs, stockers, were around $560 a pop. Ouch. Here you get all three for less than $800. AND if you have the time, you could fish 3 2300s, three side hung float bowls, and 3 30cc poump kits off ebay and maybe have $200 into all 3!!! I might just do that to do it. Build another topside setup. To see how cheaply I can do it! ( very non-Corvette, huh!)

DDennis, I never said you were wrong BTW, andb I know if you call Holley tech, they say the same thing. "cookie-cutter" advice for the masses.

Gene, thanks for the explanation; sounds like a good set-up. I still want to run a tri-power set-up, and hope to do so in the near future. When the time comes, I'm sure I'll be picking your brain. Thanks again, Wes

Originally posted by 427L88:
Dennis, like any other engineering application, there's the " commoner advice" and then there's the engineer advice. FOr the common guy who has a hard time setting a carb up, or doesnt intricately know how they work, the PV 2 below idle vaccum is fine. It's simpel advice and works OK.

DDennis, I never said you were wrong BTW, andb I know if you call Holley tech, they say the same thing. "cookie-cutter" advice for the masses. well let me say this....my experience comes from working and modifying my own carbs...as well as the many books that teaches you how to super tune and modify the holley carb.....knowing the function of every circuit is very important......in the task as to how to make the carb best for each given engine.....

right out of the book "super tuning and modifying holley carbs" this is stated:

in some instances it maybe impossible to find a power valve that will remain closed at idle, yet remain open during high-speed operation. (talking about performance cars with low idle vacuum basically under 5 inches). Occasionally the extra richness caused by the valve being open at idle may not present problems with fouled spark plugs or exceptionally erratic engine operation. given enough camshaft duration an extra shake or shudder will never be noticed. Alternately, increasing the idle speed a few hundred rpm's may bring vacuum up enough to alleviate an otherwise problematical situation.............it would appear that the change in air/fuel ratio caused by an open power valve or increased jet size should have virtually no effect on the idle circuit, which receives fuel through an orifice that is les then 1/2 the diameter (and less then 1/4 of the area) of the main jet. However, the extra fuel in the main well does tend to increase richness of the idle mixture. it can also cause a very rich off-idle condition. typically,altering jet size by a few numbers will have little effect, but increasing jet size by 6 numbers or more (as when removing power valve)or having the power valve open at an inopportune time (like at idle)can creat a noticeable difference........


so my advice for his car was not a "cookie cutter" advice.....with his bigger cam a lower vacuum at idle causes problems......now under other conditions like a engine that produces way more vacuum at idle.....the power valve opening point becomes more of a driver friendly choice were the idle isnt as choppy or struggling.....were your main concern is more or less fuel economy and added the extra fuel at the right time when you mash the gas not to go into a lean condition.......this is were i think your thinking of the power valve has no effect at idle..........but on the cars with bigger cams and lower vacuum it becomes important to not have it open during idle.....

and i can tell you for sure there is a difference when the right power valve is picked.......example a friend of mine just got his big 253@ .050 cam put in a 350 sbc with a single plane and 3310-2 carb.....with a 6.5 power valve the engine stumbled and struggled to idle down low about 600 rpms were it was making 4" of vacuum after changing the power valve to a 3.5 and readjusting his idle mixture screws the motor would idle as low as 350 rpms and the exhaust didnt smell near as bad......of course this is were it's not going to idle but it just shows in a performance application were just trying to get a cleaner idle all these little changes makes a difference.........