Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Float setting?
Jimpala:
I just ordered one of your viton needle/seat assemblies,Cliff.Would you suggest raising my float setting up to 1/4" versus the stock oem 15/32"? Would the 1/4" setting help handle my higher than desired fuel pump pressure of 7lbs. I did just find a nos ac delco #40987 pump and it's on it's way.Hopefully this new pump will bring me down to 5-6psi. My carb#17059505.It sits on a stock '76 350. Thanks,Jim
--- Quote from: Cliff Ruggles on March 15, 2014, 04:33:10 AM ---The factory float settings are often pretty "low" on the later carburetors. They were based on the original applications tuning requirements, fuel pressure, etc. Many later model set-ups used higher pressure pumps, and return systems to keep more fuel in circulation (cooling).
I would also add here that none of the over the counter rebuild kits will contain a good high quality needle/seat assembly, they aren't even the correct size for the carburetor number. Ethanol will quickly find a new part that isn't made of a good quality flouroelostomer. This also effects fuel level, float setting, etc, at any give pressure. We've also vacuum and pressure tested a lot of the seats and many aren't holding.
Just another reason why we stepped up the quality of our parts in recent years, and we have ZERO issues with any of our parts in this new fuel.....Cliff
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StillLearning:
I finished a 1983 Quadrajet with Cliff's parts and advice. The first float setting I tried was about 5/16". Way too high-gas everywhere! Went to 15/32" and it solved several running problems. The carb now works great! This allows me to work on jeweling in timing and advance without worrying about an over-rich fuel system.
Jimpala:
That is interesting,StiilLearning. In Cliff's book at bottom of page 25 and top of page 26 he states that it's best to use stock oem float settings unless building for hp. Jim
StillLearning:
I don't pretend to have Cliff's knowledge regarding Q-jets, but I have been rebuilding them off and on since the late sixties. Float setting close to or a little lower than spec has always worked for me. One thing I would add based on personal experience is most running problems are not related to just one thing. For instance if running rpm timing and advance are not right no amount of carb tuning will cure the problem. Generally speaking, carb doesn't affect timing, but timing can sure mess up how a carb works. Just a thought. :)
Jimpala:
Same here been at it a long time as well.Agree,engine perf starts with timing.Also today,I've noticed all these new oem replacement fuel pumps all seem to put out much higher pressure than they did even 5-6 years ago.I'm battling this issue right now on a stock '76 low mile 350 sbc.I've bought 7 "Stock" oem style pumps from all the popular places.ALL are putting out 8-13 psi! We know Q-jets are happy btw 4-6psi.I've given up on these new pumps they are all made in China,Mexico or Milaysia. I am looking for an NOS AC Delco pump.Not that it will last long with today's fuel and any poss diaphram deteriation,but I am frustrated......... Jim
--- Quote from: StillLearning on April 02, 2014, 06:36:01 PM ---I don't pretend to have Cliff's knowledge regarding Q-jets, but I have been rebuilding them off and on since the late sixties. Float setting close to or a little lower than spec has always worked for me. One thing I would add based on personal experience is most running problems are not related to just one thing. For instance if running rpm timing and advance are not right no amount of carb tuning will cure the problem. Generally speaking, carb doesn't affect timing, but timing can sure mess up how a carb works. Just a thought. :)
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