Quadrajet Idle Problems

[othelloears]

On my 5th problem if the year... first controls, broken impeller, shaft seal, risers/manifolds now carb. Radio won't work either but can't complain

I have a 1984 mercruiser 228 (chevy 5.0 305) with a quadrajet carb.

Runs great at high rpms but surging pretty bad at idle / low rpm's.

I removed the mixture screws to shoot cleaner and its worse...won't idle at all.

Put them in and trying to adjust but having no luck. I can basically unscrew almost all the way with no change in idle speed.

That normally means a vacuum leak correct?

Pulling the carb now to rebuild but wanted to get opinions.

Thanks

 

[Stamey]

Re: Quadrajet Idle Problems

Before you move forward, wiggle the throttle shaft for the primaries. How much wiggle does it have? With the engine running, at idle as best it can, spray the throttle shaft, where it goes into the carb, one either side. If the engine revs up and begins to run smoother, you have the worn throttle shaft syndrome, which is your vacuum leak.

This is a common problem with Quadrajets and there are many fixes out there for it, depending on how industrious you are.
I just took 3 carbs to a man for rebuilding, and he had 2 spares, and out of 5 carbs only one had a tight throttle shaft. He said he has had no luck with the bushing kits for Q-jets so he doesn't use them. I have researched it a bit and while it seems like it is possible, and a usable fix exists, I have not yet tried it myself.
http://www.garagejournal.com/forum/showthread.php?t=78157

If this is your problem, your possible solutions are getting a reman/new carb, rebuilding the old carb and trying the throttle shaft repair or rejetting the carb by a small amount to richen up the idle. I was told I'd need to go from .072 to .074 jets to richen the idle on one of mine with a loose shaft.

Chris

 

[othelloears]

Re: Quadrajet Idle Problems

Thanks so much for the detailed response/ and info. I was aware of the issue and am going to make the call after I have it apart.

I found a reman for 199$ at Nationalcarburators.com
http://www.nationalcarburetors.com/marine/fourbarrelrochester.aspx

Does anyone have experience with these guys?

 

[wilyesteve]

Re: Quadrajet Idle Problems

Just ordered one from teh same place. 4bbl manifold choke for my 350. Was cheapest by far so we'll see!

 

[othelloears]

Re: Quadrajet Idle Problems

Wilysteve how did that carb work out?

 

[joncrisler]

Re: Quadrajet Idle Problems

Thanks so much for the detailed response/ and info. I was aware of the issue and am going to make the call after I have it apart.

I found a reman for 199$ at Nationalcarburators.com
http://www.nationalcarburetors.com/marine/fourbarrelrochester.aspx

Does anyone have experience with these guys?

I have no experience with them, but they have been around for at least 6-7 years: I looked at them before back then.