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Old 05-15-2010, 03:28 PM   #1
uwti
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Default Trouble with gas fumes!

Running a 428CJ in my 67 mustang, Holley 850CFM carb, even at idle the fumes are killing me! driving the car I stink of gas, I can deal with that! but the fumes have gotten to a point that I don't even want to run the car. Don't know if the carb is set to rich, I turned the air/fuel screws clock wise to lean out, and they are almost shut tight (withing a half turn) and the fumes are still very strong.

Anyone have any advice on this?
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Old 05-15-2010, 03:32 PM   #2
nba1341
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I had strong gas fumes and smelt of gas running my car until I leaned it out a bit. You probably will need to change out the jets on the carb although with such a big engine you might want to borrow an a/f meter to get the perfect a/f ratio out of it.


p.s. you will be able to tell if your too rich by just pulling the spark plugs and seeing if there is black soot all over them

Last edited by nba1341; 05-15-2010 at 03:38 PM.
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Old 05-15-2010, 04:27 PM   #3
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You have two problems. Your carb is badly tuned, and probably too large, making it difficult to tune, and even if the stench of dead skunks was coming out of the tailpipe you shouldn't be able to smell it. You need to start checking every weatherstrip, seal, and plug on the body, especially on the back half of your car. Even if you got the carb worked out tomorrow, the CO2 would kill you on your next long drive, because you can't smell CO2.
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Old 05-15-2010, 05:07 PM   #4
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If you dont buy a A/F meter then buy a vacuum gauge. Set your timing first and hot idle. Then plug it into manifold vacuum. Set the mixture screws to give you the most vacuum at the correct idle speed. You will probably need to reset your idle a few times to get this.

And like 2+2 said make sure you have good weatherstripping. Also make sure your exaust is in good shape and exits out the back. If you just have mufflers that exit under the car the exaust will float up into the cabin.
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Old 05-15-2010, 05:19 PM   #5
67mustang302
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Sounds like the idle circuit is too rich AT LEAST. What carb? Can you change IFRs or air bleeds? What timing is it at and what's the engine setup?

Edit: post plug pics too.
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Old 05-15-2010, 05:21 PM   #6
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well ya, you shouldn't smell it. but something is clearly wrong.
if it's the exact smell of gas, then you're spilling it somewhere. check for leaks. if it's the exhaust fumes then i wonder how you smell of petrol when driving it. once you know everything is tight and you don't smell petrol through the trunk or dripping on the engine, then check the carb.

when she's warm make sure the top butterfly for the choke is fully open. turn one of the idle mixture screws all the way in. if she doesn't stall then you're getting way too much petrol where she shouldn't get any.
start with setting the fuel level. once that's done, turn idle mixture screws all the way in , then maybe 1 turn out. if you have off idle hesitation open more. when engine is idling check down the carb, you shouldn't see any fuel anywhere during idle
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Old 05-15-2010, 05:23 PM   #7
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I have leaned it out just short of the engine dying, it is now within a half turn of both mixture screws being all the way closed. Situation is slightly improved, I can take them down to within a quarter turn and adjust the idle, would this be advised?
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Old 05-15-2010, 05:25 PM   #8
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Quote:
Originally Posted by 67mustang302 View Post
Sounds like the idle circuit is too rich AT LEAST. What carb? Can you change IFRs or air bleeds? What timing is it at and what's the engine setup?

Edit: post plug pics too.


Holley 0-82851 Distributor timing has about 10-32 degrees advance I believe
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Old 05-15-2010, 05:42 PM   #9
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i'd say if you have them in that far you're spilling fuel inside the carb. checlk if there's gas coming out of the boosters in idle or something. if the idle is too lean the engine will heat and you'll have severe off idle problems. maybe you have a stuck float. try banding both fuel bowls with a screwdriver butt
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Old 05-15-2010, 05:55 PM   #10
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Set it to 12-14 for the timing, carb'd engines, especially modified, won't idle right without decent timing. And the mixture screws should not be in that far. What's your fuel pressure?

and are you adjusting all 4 idle mix screws, or just the ones on the front?
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