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Carburetors Carb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.

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Old 12-24-2007, 11:09 AM   #1
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Join Date: Oct 2003
Location: Buffalo, NY
Posts: 415
Car: 1987 Camaro IROC-Z28
Engine: TPI 350ci L98
Transmission: T56 - Hurst Shifter
Axle/Gears: BW - 3.70

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Hard Starting - After sitting overnight

Iíve got a hard starting problem with my 88 jeep wrangler. My Camaro is fuel injected and I havenít done much work on carbureted vehicles. I donít think the problem is vehicle specific so hopefully you guys can help.

It starts hard after is has been sitting for a day. I know the carburetor is adjusted properly as well as the choke. It appears to be a fuel problem. I acts like the gas is draining back into the tank after sitting overnight. It has a mechanical fuel pump and you have to keep cranking the engine until it can pump the fuel back up to the carburetor. I usually have to crank the engine for 10 Ė 15 seconds before it will start. Once it starts I can shut it off and it will start right up again without having to crank. Once started it runs and idles fine so I donít think there is any problem with the carburetor. It originally had a Carter computer controlled carburetor which sucked so I swapped it for a Webber carb. The Jeep runs much better but still has this starting problem after sitting overnight. The original setup I think was similar to the carburetors in the Camaro. It had a computer and emissions stuff, O2 sensor, egr, charcoal canister, AIR, etcÖ Iím wondering if the fuel pump is bad causing the gas to drain back into the tank.

I also was wondering if the problem might be with the gas tank. Is the tank supposed to be pressurized in a carbureted vehicle? In the summer time, after I drive the vehicle, if I take the gas cap off you can hear all this pressurized air escape from the take. Is it supposed to have this pressure in the tank? Is that what keeps the fuel from draining back into the tank when the vehicle is not running? If so, then maybe the gas cap is bad because the seal leaks and you can hear the air escaping after the engine is turned off.
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Old 12-24-2007, 11:15 AM   #2
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Join Date: Sep 2004
Location: Lakeland, FLA
Posts: 2,763
Car: 88 V6 'bird/88 IROC/85 T/A
Engine: Buick 6 swap coming/TPI sbc x2
Transmission: V8 T-5/700R4 x2
Axle/Gears: 3.42 open/3.73 posi/ 3.27 9 bolt

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Re: Hard Starting - After sitting overnight

Have you only had the problem since you swapped the carb?

Somehow, air is getting into your line where the fuel line hooks to the carb, I think. It allows the fuel to siphon back to the tank over time. I'd check the fuel lines for cracks or seepage somewhere.

Your gas tank staying pressurized is for emmissions purposes to allow the vapors to exit up front under the hood and then get drawn into the carb and burned. You have a vacuum regulator valve somehwere that is supposed to purge that pressure at a certain limit and then allow the excess pressure to be used in the engine.
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Old 12-24-2007, 12:23 PM   #3
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Join Date: Oct 2003
Location: Buffalo, NY
Posts: 415
Car: 1987 Camaro IROC-Z28
Engine: TPI 350ci L98
Transmission: T56 - Hurst Shifter
Axle/Gears: BW - 3.70

Classifieds Rating: (2)

Re: Hard Starting - After sitting overnight

No, I had the same problem with the old carb as well.

Well it's not leaking fuel anyway. None on the floor or around the engine so I can't see how the air could be getting in if the fuel isn't leaking out.

That makes sense about the emmisions. What if the seal on the gas cap is bad causing the presure to escape from the tank. Would this cause the line to drain?
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Old 12-24-2007, 01:20 PM   #4
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Join Date: Sep 2004
Location: Lakeland, FLA
Posts: 2,763
Car: 88 V6 'bird/88 IROC/85 T/A
Engine: Buick 6 swap coming/TPI sbc x2
Transmission: V8 T-5/700R4 x2
Axle/Gears: 3.42 open/3.73 posi/ 3.27 9 bolt

Classifieds Rating: (5)

Re: Hard Starting - After sitting overnight

That's the funny thing about air; it doesn't have to find it's way in only where the liquid comes out. That's why it takes so long to drain back (overnight.)

My old Buick does that as well. My carb is leaking air through the bowl vent and my needle and seat have seen better days. I live with it because the engine is coming out to go into another car.
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Old 12-24-2007, 01:20 PM
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