Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Difficult hot/wam restarts...Ethanol?
brown7373:
That sure sounds plausible. It isn't flooded to the point that it won't start, but it does struggle some, and is worse when it is hotter, which would seem to increase the pressure a little more.
brown7373:
My issues have continued and with warmer weather, a little worse. I put on my old fuel pump this morning. I replaced it because I thought it "looked" old, and I wanted to replace before it failed out on the road. I noticed immediately that it seems to start much easier when hot. Additionally, with the Air-Tex, I wasn't able to get the idle down around 600 in drive. With the old pump, it idles smoother and I can adjust idle below 600 if I wanted to. That seems on the surface to confirm it was pushing a little fuel past the inlet seat even when at idle, and certainly after shutdown. I have not yet driven it enough to be positive, but so far that sure seems to correct the issue.
I still want to buy a new fuel pump (mechanical), but almost everyone sells Air-Tex. Anyone know if anyone sells an AC Delco?
von:
Airtex is the brand I had a problem with. I bought two of them before I realized they were the problem. Even their specs show pressures that are too high for a Q jet.
brown7373:
It seems like it is harder and harder to find mechanicals that are NOT Air-Tex. Many of the parts stores in my area sell Air-Tex, including NAPA. I also have one on my 1970 Bonneville 455 that I will soon be starting to break-in the cam. I purchased an AC from ebay and plan to switch it today before I start the engine.
Cliff Ruggles:
We have been getting a LOT of complaints to the shop in recent years concerning currently available mechanical fuel pumps.
One customer that we built two BBC Marine units for actually sent one of them back because it flooded after shut down, difficult to start cold or hot, and running issues. We tested the carb and it was flawless, returned it to him, the troubles continued. I had him swap the good working carb from the other engine and it started acting up. Turns out the culprit was the "new" fuel pump, the other pump was also new, same manufacturer, and working fine.
So before replacing the pump he did a fuel pressure check, it was around 10-12 psi, not 5-6 like the other one......Cliff
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