carb drain back
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Registered User
Joined: Sep 2013
Posts: 3,645
carb drain back
My buddy has a problem with his quadrajet draining back. There is a new gas tank , new fuel lines, new vent line, new fuel pump. I think the manual fuel pump is a carter. I looked at what he has and i am at loss why he has this problem. Joe Padavano anyone else got any ideal what is causing this if the car sets 2/3 days.
Registered User
Joined: Oct 2009
Posts: 216
From: Southern Ontario
Had the same thing happen to me. It turned out not to be draining back, the bowl was leaking into the intake.
Test:
Run the motor, shut it down. Crimp the rubber line to the fuel pump. Let sit for a few days. Remove the crimp devise and try and start car.
If it starts quickly, the fuel is draining back to the tank. Replace the fuel filter with one that has the back flow valve.
If it still takes takes a long time to start, the fuel is leaking into the intake.
Rebuild carb
Joe
Test:
Run the motor, shut it down. Crimp the rubber line to the fuel pump. Let sit for a few days. Remove the crimp devise and try and start car.
If it starts quickly, the fuel is draining back to the tank. Replace the fuel filter with one that has the back flow valve.
If it still takes takes a long time to start, the fuel is leaking into the intake.
Rebuild carb
Joe
Registered User
Joined: Dec 2015
Posts: 109
From: Waring, Tx
Keep in mind, fuel evaporation can be a contributing factor also.
And like Joe said, some of the well plugs do leak, but most after 70 do not.
Make sure float level is set high enough to allow most fuel in the bowl. The 60's and early 70's Olds Quadrajets still used the large float, so there is less fuel in bowl.
Make sure the clip is not on the needle, holding it to the float. This will allow the needle to sit in seat unless fuel is flowing in to the carb. The clip was necessary 40 years ago but not necessary with todays fuels in my opinion and experience.
Hope this helps.
And like Joe said, some of the well plugs do leak, but most after 70 do not.
Make sure float level is set high enough to allow most fuel in the bowl. The 60's and early 70's Olds Quadrajets still used the large float, so there is less fuel in bowl.
Make sure the clip is not on the needle, holding it to the float. This will allow the needle to sit in seat unless fuel is flowing in to the carb. The clip was necessary 40 years ago but not necessary with todays fuels in my opinion and experience.
Hope this helps.
Old(s) Fart
Joined: Mar 2007
Posts: 50,803
From: Northern VA
Also, be sure the fuel pump is in good shape. Ethanol can cause the rubber check valves in the pump to leak, requiring much longer cranking times to start fuel flowing to fill the carb.
The "leaking well plugs" on Qjets has been a boogeyman ever since Doug Roe wrote about it. In nearly five decades of working on these cars, the ONLY Qjet I've ever seen with this problem is the one on my 67, which has the stamped steel plugs, not the spun-in aluminum ones used from 1968-up. I've gotten the repair plugs with the o-ring seals for this one.
If you REALLY think your carb is leaking, prop it up over a piece of paper, fill the bowl, and let it sit overnight. If the paper is dry, leakage is NOT your problem. Simple, free test before jumping into expensive and possibly unnecessary repairs.
The "leaking well plugs" on Qjets has been a boogeyman ever since Doug Roe wrote about it. In nearly five decades of working on these cars, the ONLY Qjet I've ever seen with this problem is the one on my 67, which has the stamped steel plugs, not the spun-in aluminum ones used from 1968-up. I've gotten the repair plugs with the o-ring seals for this one.
If you REALLY think your carb is leaking, prop it up over a piece of paper, fill the bowl, and let it sit overnight. If the paper is dry, leakage is NOT your problem. Simple, free test before jumping into expensive and possibly unnecessary repairs.
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