Fuel Smell after running. Carb Issues? - Chevelle Tech
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post #1 of 31 (permalink) Old Jan 19th, 19, 4:30 PM Thread Starter
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Fuel Smell after running. Carb Issues?

I have a 70' SS 454 with a Holley 650 DP carb. After I go for a drive and come home, put the car in the garage and go back out in the garage a while later, I smell what appears to smell like hot gas. Not really a raw gas smell, but something like fuel is sitting in the carb and not burnt. My question is, is this normal? The motor dynos at 430 hp at the crank. I don't know the history on the motor. My other question is, is this under carbed? My primary jets are 70 and secondary are 74. I had it re-jetted from 73 and 77. I am thinking of another carb also. Any thoughts on maybe carb replacement or rebuild? Thanks Guys
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post #2 of 31 (permalink) Old Jan 19th, 19, 11:08 PM
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Re: Fuel Smell after running. Carb Issues?

Not sure I have ever heard it described like that.

If your car has a fairly large camshaft then if might just be the typical overlap smell that these cars make.

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post #3 of 31 (permalink) Old Jan 19th, 19, 11:24 PM
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Re: Fuel Smell after running. Carb Issues?

Do you have headers? I've noticed what you describe on my 'Bu since I put headers on her.

A 650 CFM is a byte on the small size for a performance application... However, you'll likely get better gas mileage with it. You could get yourself a nice Holley 750 or 770. If you have an automatic you'll want a Vacuum Secondary, but if you have a stick, you may be able to run a Double Pumper with Manual Secondaries...

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post #4 of 31 (permalink) Old Jan 20th, 19, 12:56 AM
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Re: Fuel Smell after running. Carb Issues?

The fuel smell could be the floats are too high and your dribbling or leaking fuel from the carb. It could also be old dried and cracked rubber fuel lines at the tank or the fuel pump.

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post #5 of 31 (permalink) Old Jan 21st, 19, 4:58 PM Thread Starter
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Re: Fuel Smell after running. Carb Issues?

My car is a 4-speed. The current carb is a Holley 4150 650 double pumper. Although I don't know the specifics about the motor, I have been told that several mechanics think it has a mild cam. The carb has mechanical secondaries. Are there advantages or disadvantages to a mechanical vs vacuum secondary? I am leaning toward a Holley 750 double pumper with mechanical secondaries, and I have also been told that Edelbrock uses vacuum secondaries but that carb will lose about 30-40 horsepower. Any truth to that? Thanks
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post #6 of 31 (permalink) Old Jan 21st, 19, 5:08 PM
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Re: Fuel Smell after running. Carb Issues?

1970 Chevelles designed for use in Calif were equipped with a charcoal canister located in the left front side engine compartment. Do you have a charcoal canister in that position? Where was your Chevelle built? Do you still see a tune up or emissions label on the radiator cover?

The above info will determine the type of tank vent system installed. Of course someone could have changed to a different tank or vent system or yanked the charcoal canister.

What type of air cleaner is currently installed on the car? Some are more susceptible to release of fumes.

Other issues have been mentioned by posters above.
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post #7 of 31 (permalink) Old Jan 21st, 19, 7:37 PM Thread Starter
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Re: Fuel Smell after running. Carb Issues?

The car was built in Atlanta. It had a rotisserie restoration in 2011. It does not have a charcoal canister. The 454 is a GM Warranty replacement engine. It has a CEV code on the block. Unfortunately, the person I got it from two years ago did not have any information about the restoration. This is a Sunday afternoon driver and every once in a while to dinner car. I don't race it. I am just looking for best performance. It actually runs good, the electric choke is a joke. I was also considering fuel injection. I keep seeing too many issues with that. If I have to rebuild the carburetor, I am just going to get a new one and upgrade to a 750 or so. I am just looking for more user friendly. That's all. Thanks
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post #8 of 31 (permalink) Old Jan 22nd, 19, 4:33 AM
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Re: Fuel Smell after running. Carb Issues?

Edel carbs are mech secondary carbs, like a QJ.

Was it a Holley salesman that said the E carb would 30-40 hp over the E carb....
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post #9 of 31 (permalink) Old Jan 22nd, 19, 4:53 AM
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Re: Fuel Smell after running. Carb Issues?

Quote:
Originally Posted by Gtogeoff View Post
Edel carbs are mech secondary carbs, like a QJ.

Was it a Holley salesman that said the E carb would 30-40 hp over the E carb....
Dont understand?
E carb would 30-40 hp over the E carb....


Is that the carb you have on your Chevelle? Please post some info about it Im during to see some poctures of it.
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post #10 of 31 (permalink) Old Jan 22nd, 19, 5:01 AM
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Re: Fuel Smell after running. Carb Issues?

Maybe the small comes from heat? Try a heatshield or phenolic spacer 0.5. Or from the hoses some hoses dont like ethanol and lets gas fumes go threw the rubber.

The 650 might be on the small side but if you never race it you wont notice the difference going biggger. Rune what you have.
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post #11 of 31 (permalink) Old Jan 22nd, 19, 5:52 AM
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Re: Fuel Smell after running. Carb Issues?

IF you change carb its hard to beat a holley 3310 750, its about as perfect as possible on a mild 454. If your intake has dual pattern a quadrajet is another great option.
But follow the advices above before you runs out and buy a new carb.
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post #12 of 31 (permalink) Old Jan 22nd, 19, 3:04 PM Thread Starter
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Re: Fuel Smell after running. Carb Issues?

The cars does not have headers. The carb is a 4150 650 double pumper. Mechanical secondaries. I just got back from a local shop and spoke with them. They also said the carb is too small for the engine. Here is what they recommended.



https://www.holley.com/products/fuel...parts/BR-67257


They definitely told me to stay away from fuel injection. They actually have a Holley Sniper they installed on a car right now and said they are having all kinds of issues. They didn't mention what issues. They assured me that the carb listed above is virtually trouble free. It apparently has more adjustment than the 3310 series. Thanks
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post #13 of 31 (permalink) Old Jan 22nd, 19, 3:27 PM
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Re: Fuel Smell after running. Carb Issues?

Quote:
Originally Posted by cyclerider View Post
The cars does not have headers. The carb is a 4150 650 double pumper. Mechanical secondaries. I just got back from a local shop and spoke with them. They also said the carb is too small for the engine. Here is what they recommended.



https://www.holley.com/products/fuel...parts/BR-67257


They definitely told me to stay away from fuel injection. They actually have a Holley Sniper they installed on a car right now and said they are having all kinds of issues. They didn't mention what issues. They assured me that the carb listed above is virtually trouble free. It apparently has more adjustment than the 3310 series. Thanks
The shop likely does not know much about EFI and are learning on go....JMHO

That Sniper setup is pretty popular in my area and the local shop made a trip to Holley to learn how to tune EFI since they were always a carb shop....been going well with the EFI tuning now.
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post #14 of 31 (permalink) Old Jan 22nd, 19, 3:51 PM
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Re: Fuel Smell after running. Carb Issues?

I think a 750 double pumper will serve you well. I've never used a Brawler, but it appears to be a good carb.

It may not eliminate your fuel vapor/smell issue, but it's a start.

Your car should have a vented fuel cap. Sometimes not using one will cause the built up pressure in the tank to force fuel though the carb needle after you shut the car down. If you get a chance, a picture of the fuel vent system that might be located right front side of the fuel tank just behind the axel will help narrow down which tank you have. That will help determine what tank is actually in the car since it may have been changed with the tank from a different year. From there, a suggestion in venting methods can be given.

The lower attachment or 3rd attachment shows the 70 Chevelle tank without EEC system that should have come in most non California destined Chevelles. This tank without the extra fittings on the right front must be used with a vented gas cap. Note there are no vent pipes that come out of the right front side of the tank. Others show location of fuel vents and tanks with vent hose/return line provisions used in other years and EEC equipped Chevelles. EEC being Evaporative Emissions Control which was required on the 70's destined for Calif use.
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post #15 of 31 (permalink) Old Jan 22nd, 19, 4:28 PM
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Re: Fuel Smell after running. Carb Issues?

Forgot.........If you do take a look at the tank, see if there are pipe nipples coming from the center front and/or left front of the tank.

Check your hoses for signs of leakage or deterioration. Sometimes you'll see stains or dusty/dirty accumulations in leakage ares.
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