Fuel/exhaust smell
Thread Starter
Le Mans Master
Joined: Jun 2019
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From: Loveland
Fuel/exhaust smell
68 327 350 hp, holley spread bore carb, stock side pipes. Since I got the car, when driving you can smell the exhaust a bit. Sitting in the garage you can smell gas or exhaust. Is this just the nature of the beast? Did they do this when new? I'm going to do a check of the exhaust system from the manifold to the end for leaks. After that I'm sure it could be a 1000 other things.
Last edited by kodpkd; Sep 20, 2020 at 09:11 AM.
Le Mans Master
Joined: Jun 2019
Posts: 7,658
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From: Indiana
Not sure exhaust would matter if leaking or exiting correctly when pulling in garage..
i would inspect fuel lines and nose finger wipe smell test..
then the 1000 others..
i thought mine smelled of exhaustand gas and was sneaky leaking gas lines that were not visual..no more smell...
i would inspect fuel lines and nose finger wipe smell test..
then the 1000 others..
i thought mine smelled of exhaustand gas and was sneaky leaking gas lines that were not visual..no more smell...
Last edited by interpon; Sep 20, 2020 at 09:48 AM.
Thread Starter
Le Mans Master
Joined: Jun 2019
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From: Loveland
I would say they are both pretty black. I suspect the engine is original and might be burning a little oil, but not sure if this would make it smell. I have done work on the gas lines and didn't think they were leaking. I can check again.
Race Director
Joined: May 2006
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The black could also mean rich which would account for the smell.
How is your timing set, just to stock, more advanced, recurved?
Is your vacuum advance connected to manifold or ported?
Exactly what list# carburetor?
Do the idle mixture screws when turned clockwise cause a drop in idle speed and eventually stalling?
Stock cam?
How is your timing set, just to stock, more advanced, recurved?
Is your vacuum advance connected to manifold or ported?
Exactly what list# carburetor?
Do the idle mixture screws when turned clockwise cause a drop in idle speed and eventually stalling?
Stock cam?
Last edited by MelWff; Sep 20, 2020 at 01:48 PM.
Safety Car
Joined: May 2001
Posts: 4,759
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From: Fairfax Virginia
I was having issues with my 1968 C3's 427 smelling rich at times so I installed an Air-Fuel Ratio gauge. This helps you really get the most out of the carburetor as you can see just how it is running.
My C3 has a Vented gas cap which will release fumes and in a sealed Garage you will smell gasoline, not the garage has ventilation to avoid that issue.
The combination of the the 1968 with the 327 is probably my favorite revving engine built by GM.
My C3 has a Vented gas cap which will release fumes and in a sealed Garage you will smell gasoline, not the garage has ventilation to avoid that issue.
The combination of the the 1968 with the 327 is probably my favorite revving engine built by GM.
Racer
Joined: Jun 2020
Posts: 293
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From: Highland Village, TX
St. Jude Donor '21
I have a new to me 74 with a rebuilt engine. Had the same issues with exhaust and gas smells. With a car this old things naturally shake loose. I tightened down exhaust manifolds, oil pan, fuel lines etc. All helped but what helped the most was setting timing properly. Still some exhaust smell because we have no cats but not overbearing like it was.
Mine was set at 0 degrees initial timing.
Mine was set at 0 degrees initial timing.
Thread Starter
Le Mans Master
Joined: Jun 2019
Posts: 5,485
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From: Loveland
The black could also mean rich which would account for the smell.
How is your timing set, just to stock, more advanced, recurved?
Is your vacuum advance connected to manifold or ported?
Exactly what list# carburetor?
Do the idle mixture screws when turned clockwise cause a drop in idle speed and eventually stalling?
Stock cam?
How is your timing set, just to stock, more advanced, recurved?
Is your vacuum advance connected to manifold or ported?
Exactly what list# carburetor?
Do the idle mixture screws when turned clockwise cause a drop in idle speed and eventually stalling?
Stock cam?
Vacuum advance to manifold.
4175 Holley
Yes the metering block screws will cut the fuel off, set to about 1 1/2 turns out to max idle vacuum.
Stock cam.
I think I will check the exhaust bolts to the manifold.
Last edited by kodpkd; Sep 21, 2020 at 09:49 AM.
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Race Director
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What is the list# of the 4175, that is the model #.
Look at the front of the airhorn.
Using Lars set up what initial timing are you running?
You confirmed that the vacuum advance works?
Look at the front of the airhorn.
Using Lars set up what initial timing are you running?
You confirmed that the vacuum advance works?
Last edited by MelWff; Sep 21, 2020 at 11:20 AM.
Thread Starter
Le Mans Master
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From: Loveland
Vacuum works!
I'm not exactly sure about the timing. What ever Lar's said. I think 25* initial.
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Cruise-In VIII Veteran
Sounds to me like it smells like a Car! Bloody oath. It runs on gasoline and makes exhaust. Harden up princess!
Race Director
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If the exhaust outlets are black it's running rich but hard to pinpoint why since timing and carburetor seem correct.
Have you ever tried adjusting the mixture screws based on getting an rpm drop and then backing off rather than using a vacuum gauge?
Have you ever tried adjusting the mixture screws based on getting an rpm drop and then backing off rather than using a vacuum gauge?
Thread Starter
Le Mans Master
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From: Loveland
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The main jet ,if the carburetor hasn't been modified is a 62, and should be fine. The power valve, 6.5, isnt blown since the idle mixture screws effect the idle as you turn them in.
You can't check the float level unless you remove the bowls.
Do you notice gasoline dripping down the carburetor throat at idle or immediately after shut off?
You can't check the float level unless you remove the bowls.
Do you notice gasoline dripping down the carburetor throat at idle or immediately after shut off?
Last edited by MelWff; Sep 22, 2020 at 08:23 PM.
1967 Pedal Car Champion
Joined: Mar 2020
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From: US-PNW
RE: the smell while in the garage
Can you better define what you smell? Raw gasoline or car exhaust?
Exhaust smell is likely a condition of less than complete burn of the fuel - very carbon black, sooty exhaust pipes and spark plugs. Full tune-up to solve issue.
Raw gas is probably a leak somewhere or a poorly sealing gas cap. Check every connection fitting for fuel stains. Even though you have a vented cap (or should, in a stock '68), the cap gasket should seal against the filler neck.
Also, keep in mind that these cars do not have the emission controls that modern cars have. Their gasoline burn efficiencies are much less complete and will generate a higher degree of "ambient" fuel/exhaust smell - but it shouldn't be so strong as to force you from the garage or cause health concerns over the vapors you're breathing.
Can you better define what you smell? Raw gasoline or car exhaust?
Exhaust smell is likely a condition of less than complete burn of the fuel - very carbon black, sooty exhaust pipes and spark plugs. Full tune-up to solve issue.
Raw gas is probably a leak somewhere or a poorly sealing gas cap. Check every connection fitting for fuel stains. Even though you have a vented cap (or should, in a stock '68), the cap gasket should seal against the filler neck.
Also, keep in mind that these cars do not have the emission controls that modern cars have. Their gasoline burn efficiencies are much less complete and will generate a higher degree of "ambient" fuel/exhaust smell - but it shouldn't be so strong as to force you from the garage or cause health concerns over the vapors you're breathing.
Le Mans Master
Joined: May 2007
Posts: 5,029
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From: North tonawanda NY
I have a new to me 74 with a rebuilt engine. Had the same issues with exhaust and gas smells. With a car this old things naturally shake loose. I tightened down exhaust manifolds, oil pan, fuel lines etc. All helped but what helped the most was setting timing properly. Still some exhaust smell because we have no cats but not overbearing like it was.
Mine was set at 0 degrees initial timing.
Mine was set at 0 degrees initial timing.
Thread Starter
Le Mans Master
Joined: Jun 2019
Posts: 5,485
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From: Loveland
The main jet ,if the carburetor hasn't been modified is a 62, and should be fine. The power valve, 6.5, isnt blown since the idle mixture screws effect the idle as you turn them in.
You can't check the float level unless you remove the bowls.
Do you notice gasoline dripping down the carburetor throat at idle or immediately after shut off?
You can't check the float level unless you remove the bowls.
Do you notice gasoline dripping down the carburetor throat at idle or immediately after shut off?
It didn't come with a charcoal canister.
Last edited by kodpkd; Sep 23, 2020 at 09:31 AM.
Race Director
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if you still have a 62 drop it down to a 59, 60 largest.
Last edited by MelWff; Sep 23, 2020 at 03:07 PM.
Le Mans Master
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2023 C3 of the Year Finalist - Modified
Thread Starter
Le Mans Master
Joined: Jun 2019
Posts: 5,485
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From: Loveland