the gas tank vents through the charcoal canister with a non vented gas cap, if you plugged the canister lines and still have a non vented cap the the fuel rubber hoses might be closing shut on ya.  

Kinda sorts sounds like a plugged fuel filter that settles after sitting and takes a while to get plugged up again. Ever have the tank down?

The charcoal canister was removed but I left the line open. I even blew compressed air through the line.

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How about the small fuel filter inside the (Q-Jet) carb?

I dropped the fuel tank back in August when this problem first developed. The tank was clean and in good shape. I did replace the screen on the pick-up tube at that time. The filter at carb. was replaced recently too but I will check it again.

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The return line is to keep from having too much dead-head pressure at the carb, AND it helps cool the fuel so vapor lock isn't an issue.
If you're just looking at the fuel going back thru the return line, it may seem like a lot, but consider that the carb doesn't really need an abundant flow of fuel while idling.
You may need to install a fuel pressure gauge at the carb and drive it, and see what the pressure is when the problem appears. You may also want to block the return line for a test and see if it has any effect,and maybe even leave the gas cap loose.
Have you blown thru the actual fuel supply line from the tank to the pump, or otherwise checked it for restrictions? How about the rubber line from the frame to the pump? Is there a kink in it?

Seems like we're all looking for a fuel problem, when it may not be one. The pressure reading will confirm that. If the fuel pressure is not dropping when the problem occurs, the the fuel system is fine, and we need to concentrate on another area...


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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

I have a Q-Jet and found the problem was the choke getting sucked shut on high RPM. Let it warm up to choke full open then jam your choke wide open with a piece of cardboard matchbook or something similar. Then hammer the thing and see if it goes away. I had my Q-Jet professsionally rebuilt and it acted up on me again this spring at Beech Bend Dragstrip.... Jammed the choke open and no more problems. The guy who rebuilt mine pop riveted the spring tension adjustment on and I have to drill out the pop rivets to tighten the spring tension, which I haven't gottn around to.

Dave

BTW... Don't buy these guys poo-pooing your Q-Jet... It's the best street carb ever....

Dave

I installed the fuel pressure gauge in a way that would allow me to read it while driving. I found that pressure would drop to 0 psi. during accelleration. Then I started looking at fuel lines (again). I noticed that the rubber line going from the steel line to the pump looked a little flat. Once I replaced that hose the problem went away. I still can't believe a .50 cent hose could cause me so much grief. On a more positive note, my baby is running again, the odometer has at 1000 mi. less than it would had I solved the problem sooner, and I found the original build sheet when I dropped the tank, and it was still legible.  Thanks for all of of your input.

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[QUOTE=DStoffel]No intake mods. Original Rochester Quadrajet. Had it rebuilt 2 years ago right after I removed what was left of the emission components (charcoal cannister and items related to the exhaust system). Car Was running great until last month.  At operating temp. I tried to maintain 2500 rpm while manually closing choke about 3/4 and it still stalled out after a minute or2. [/QUOTE]

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Brian - NCM Lifetime Member

73 coupe L48, Flat-top pistons, Performer RPM Heads, Crane Cam and roller rockers, Holley 650 vac sec. Performer intake,
3.55 gear BTO 200-4R trans,
Leather seats, Seatbelt Plus 3point seatbelts, Pioneer CD player
Magnaflow Exhuast System

My 1981 with the ECM and Q carb had almost the same symptoms.  Had the ECM replaced, did not fix problem.  Had the carb rebuilt.  She has been running great ever since.  I still have all original componants of the emmissions system.  She is stock, inside and out.

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