70vetteinpieces

I have an 1975 Oldsmobile Delta 88 convertible with a 350 rocket V8.
Having issues with fuel. Rebuilt quadrajet.

It will run well and then start sputtering like its running out of fuel with light to moderate acceleration.

Taped a fuel gauge to the windshield with mechanical pump pressure at the carb was 3 1/2 to 5 lbs. When it starts acting up the pressure was near 0. Replaced the pump - same problem. Checked the lines and charcoal canister all clear. Ran without gas cap - no difference. Put an electric pump on and bypassed the mechanical pump now get 6 lbs at the carb but under moderate acceleration drops under 3 lbs and starts sputtering like out of fuel. with electric pump I was expecting a steady reading. there is no return line.

next I ran a hose into the filler tube directly to the electric pump. same thing fuel pressure would vary. Thought issue might be with pickup tube

put a t fitting before the pump and hooked up the pressure gauge. expected to get a vacuum reading but shows about 3lbs pressure.

Any clues to what is going on? Any suggestions for another test to find the problem?

The boss

Was the problem the same (sputtering) after you ran a hose into the filler tube directly to the electric pump? Have you hooked the electric pump to the old fuel line or did you ran a new line to the carb? Long ago I had a similar problem with a customers car, I found my problem using a jerry can, ran a line to the fuel pump and the car was ok, I blew all the line and found pieces of rubber. The inside of rubber line had started to deteriorate that was causing a restriction Good luck

Patsgarage

I would eliminate the entire fuel system on the car itself by running a pump directly to the carb inlet from a fuel container with new hoses, see if the problem is still present. From what you are describing it sounds like it is starved for fuel, is the filter in the Qjet clean and installed correctly ? Also, was the problem present before the carb rebuild ?

capevettes

Who rebuilt the Q-Jet? There aren't many who do it properly. If it's one of the re-manufactured Q-Jet rebuilds it likely was done improperly. Lars Grimsrud in Colorado knows how to do them Do a search (Lars) over in the C3 section. Lots of happy customers including me. It could be a fuel line obstruction but I'm betting on the Q-Jet as the issue. Good luck.

70vetteinpieces

new fuel line going to electric pump. located pump near and below gas tank. Still used old line going to carb. But I checked it out with air and did a volume test pumping a few gallons of gas out in a clear bottle. Did not see any particles. 3 carbs - last one I got a kit and rebuilt it myself. Same issue will all 3. I know Lars is good but thought he retired from the q-jet business?

capevettes

I'm not sure if he's still doing the carbs. I thought he was. You can always try a Holley Spreadbore. I have one on my 68 427/390 Vette. Great carb.

hipocars1

Maybe the filter sock on the sending unit is clogged.

Patsgarage

If the issue has been present with three different carbs it has to be in the lines somewhere, Hippo may be on to something with the pickup in the tank. As I said before take the entire existing fuel system out of the loop and see what happens.

70vetteinpieces

ran a hose through the filler neck and connected direct to fuel pump - bypassed the pickup tube. Still curious why pressure on inlet side of pump. Tomorrow moving gauge to immediate outlet of pump to see if the readings are consistent. If so then I know I have something going on in the line under the car. always a southern car so no rusty lines and did not see any repairs made to the line. all rubber hoses have been replaced

70vetteinpieces

I think I have a crack in the intake manifold. It's getting so hot it's boiling the fuel in the carb. Put a clear filter near the carb. almost full when cold but as it warms up it starts to drain and then I see bubbles.

cv67

There is an accelerator pump out I believe that handles the stuff in todays gas a little better than the rebuilder kits that can give you the same symptom you have. A heat shield under the carb will help too.

People debate the gas is the same beg to differ

When mine gets to about 190 it doesnt want to idle anymore and no high heat underhood, anything under that its flawless. Had the car for a long long time and never had problems way back when the car would run warmer

Lars at least told to me only works on certain yr/model Qjets, try paging him in C3 tech. If he cant let Google Bob Jennings (north hills ca) is local, you can send it to him guarantee it will be perfect when you get it back .Have used im many many times
Has sun machines to curve distributors, old timer who has a racing history and decades of experience.