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Discussion Starter #1
Since my rebuild of my 396, the exhaust always smells really rich, almost gagging. Its terrible. So I jetted down the carb and it made no difference. It has 69's in the front and I think 79's in the rear. I know this is way too small, or so I have been told. First, what would cause this? Second, should I jet it back up? I was thinking around 74-84's.

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What carburetor? Did you adjust the idle mixture screws? It may be missfiring which is making you think its rich cause it smells like gas. This can be caused by being too lean among other things.
I have an 850 DP with 68 mains in it.

HTH
 

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give me the holley numbers off airhorn and i will look it up so you know whhat holley starts with

holley specs say 60 primaries/64 secondaries for my 4011 650cfm but that is a spreadbore!

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[This message has been edited by 70 SS 454 (edited 12-28-1999).]
 

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Discussion Starter #4
It is a Holley 750 double pumper. The mixture screws seem to do very little. I dont think its misfiring, but who knows? Its so rich that I am covered in rich exhaust smell everytime I get out of it(side pipes). And I am not very knowledgable when it comes to tuning carbs, pretty much anything else though.
 

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Discussion Starter #5
The model # is 80779.
I think when I jetted it down, it had 71 in front and I cant remember the back. If it matters, but I think the carb is fairly new, so I don't think its in need of a rebuild.
 

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Discussion Starter #6
Sorry I made a mistake, its #4779-6.



[This message has been edited by bigyellow (edited 12-28-1999).]
 

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If you can smell bad awful exhaust, then it means that you are either in the garage or chasing the car down the street! If it is in the garage, then just try leaning ou the idle ; if it is the other just run faster!
 

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Discussion Starter #8
It doesnt matter where the car is. If its outside and running and I walk by it, I am about to die of the smell. It cant be run in a garage for more than about 10 secs. or you will be dead from the odor. Its bad. In a sick sorta way I kinda like it, cause its smells sweet like race gas(93 octane), but then I wake up and smell the roses...uh err
gas.

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Bigyellow, it could 'possibly' be one of the following that you might double check if you haven't already:

1. Blown PowerValve - if the primary and/or secondary powervalve(s) are ruptured, they will drip raw fuel into the intake manifold and create a rich condition like you are describing (been there and done that one twice). You can check em' with a vacuum guage or do what I do...clean off the gas and suck on em'
to see if you can still move the plunger. If its' blown, you will hear air being sucked passed the blown diaphram and plunger.

2. High Float Level - If your primary or secondary float levels are set too high, the carb will be running rich as well. BTY, with your set-up, I would think that your primary jetting number should be in the 72-74 range. Secondaries are close to ideal. Hope this helps and hope you find the 'stinker' soon.


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1970 Malibu - 383 'Fog Fed' Brute Force Chevelle. Houston, Texas...Gold Member #39
 

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Discussion Starter #10
I have had the carb apart once and I checked the powervalve "by sucking on it" and it seemed fine, but for safe measure I replaced it anyway. I think the float is right below the sight glass, but I will have to check that again tomorrow. Maybe it is too high.
 

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If you stick your finger in the tailpipe and touch the inside is it black? if so it certainly is rich. Can you make the engine stall when you turn the mixture screws all the way in. I'm nervous about the fact that the mixture screws didnt make a difference. It should have at least gotten worse or better but not stayed the same.
 

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If you are getting the smell of pure gasoline, then it might be your fuel pump. If it has developed a leak you can most certainly smell it.
 

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The sure way to tell how it is running is by pulling a plug or two and looking at them. If it is indeed running rich, there will be black soot on the porcelain part of the plug. Then go from there.

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[This message has been edited by Tom Kordick (edited 12-29-1999).]
 

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Discussion Starter #14
OK, yes the tailpipes are black and sooty. The smell is not raw gasoline, so I don't have a gas leak. Since rebuilding the engine I have changed the plugs once and getting ready to change them again. Since I jetted it down the plugs were not quite as black as before, but are not optimum color. I'm gonna try and mess w/ mixture screws some more today.
 

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Try getting a edelbrock 750 performer series
carb...I had a holley 750 on for a while,took
it off the edelbrock is alot easier to adjust
stuff...and doesn't suck up as much gas.
 

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Assuming the timing ( double check ) and fuel mix os OK could it be just some oil in the exhaust and a lopey cam. Not for nothing, but on a cold start being in a garage with my old 427 is like the tear gas training hut at boot camp. But mixture is good and it moves a little oil. Cold running conditions in my mill are asphixiating (sp?).
BUT I LIKE IT


Does engine temp matter? With my mill it's "normal" when cold.

Also, make sure your idle vacuum isn't lower than the power valve rating.



[This message has been edited by Gene Chas (edited 12-29-1999).]
 

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Discussion Starter #17
It may be a little oil burning, it seems to smoke a little til its nice and warm. It also does have a lopey cam, would that contribute to it?
 

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You have checked to be sure the choke is all the way off when hot, and adjusted right for cold conditions ? Is it running smoothly ?? any bad restrictions in the intake tract like ratsnests or clogged filter??Just thinkin.


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BigYellow. All I know is that my 427 is jetted OK, carb works fine, but the cam has some overlap, and I'm sure a leak down would show the engine is getting a bit loose. So like I said, if I have her pointed ass in the garage and fire it cold, it's like the tear gas hut. Much better when it's warm. But I never "smell" the exhaust when it's not running and/or not cold. So you may simply have the same engine characteristics ( for lack of a better term I consider my L88 "dirty" running ) and a leak into the cabin through either the floor or, most likely, the trunk.

All I know is that the faster my mill warms up the better off she is, so I've gone to a 180 thermostat from the 160. If your engine is running cold, you may want to bump it up a step as well.

BTW my car doesn't have a choke, so cold idle quality is doubly bad and I have to be careful to not take my foot off it if until it warms up enough to hold 10" at idle. If not, it bumps my #85 power valve open.

Hope this sheds some light on your situation.
Check it out.

[This message has been edited by Gene Chas (edited 01-03-2000).]
 
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