Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Choke Pulloff - Marine Carb just rebuilt

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5stareventsdj:
I've been trying to diagnose a WOT problem. Problem is I'm not getting the rpms that I should. Under load I'm getting 3900 rpm max when I should be seeing 4200-4600 at my configuration. I think I may have tracked it down to the secondary air plates not openening. Is it possible that the choke pulloff is holding these closed? I see the linkage that travels between these plates and the choke pulloff. For me to open the choke plates the pulloff needs to be extended. It currently is retracted all the time. Or at least it seems to be. Is this choke pulloff supposed to weaken at low vacuum? At what rpm should the choke pulloff start to release and when should the air flaps open? Do I have this all backwards in my head?

Greg

5stareventsdj:
I got this on another quadrajet post: "When the engine fully warmed up, the choke flap should be straight up and down. This is the full open position. This is important because there is a secondary lock-out that prevents the secondary throttle blades from opening if the choke is still applied." My choke is opening fully (straight up and down). Is it possible the my flaps are still being locked. Trouble shooting further, with the engine running a cannot push the air flaps open easily as the pullof if retracted. With the engine off, the pulloff extends and the flaps open. I got brave (or possibly crazy) and hit the throttle a couple of times and didnt see the plate open. I didn't hold the throttle open though it was just a quick acceleration and backed off immediately.

Thanks,
Greg

Shark Racer:
The pull off will lose vacuum when the engine goes into high load (aggressive throttle/WOT, triggering the secondaries will likely cause this to happen).

You should measure the retraction time of the pull off and get it to 3 sec or faster (cliff's book has guidelines depending on the build you're going for.)

To do this, retract the pull off arm manually and cap the vacuum port on it with your finger. Let go and time the time it takes to fully retract.

The next step is to get the air valve tension set up correctly. I believe 3/4-7/8 turn past the point the spring engages the rod is a decent starting point.

It's not so much RPM as it is load, CFM demand. A 454 would likely open the secondaries up sooner than a 350, given equal "temperament".

Good luck, I'm a newb so my advice probably isn't great! ;)

5stareventsdj:
Thank you for the reply. Its as good as any place to start although I think I may have a problem with the mechanism that locks the secondary air valves. I will make those adjustments though and report back.

Greg

Cliff Ruggles:
I would remove the lock-out on the Marine carb if present.  It is only there to prevent the secondaries from coming in when the engine is cold and choke not fully open.  They can hang-up and cause issues.

Also check the link going from the pull-off to the air flap shaft.  It must hold the flaps tightly shut at idle (high vacuum), and allow them to fully open at full throttle (low vacuum).  Bend the rod as needed so it allows this to happen......Cliff

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