Quadrajet issues... Help?

[cadunkle]

I have an '89 Marlin Cobra 21' with a 350 Chevy Mercruiser and Alpha One. The boat is new to me and not seeming to be running quite 100%. I sprayed the air bleeds and carb in general with carbcleaner and readjusted the idle. Much better. It had the throttle plates opened so far the idle screws did nothing, and one was open about 5 turns. Anyhow idle is much improved now though still seems rich. Idle screws are still not as responsive as I would expect. I wonder if the bowl plugs are leaky?

In any event, my main issue at the moment is that the boat does not have the top end I would expect. When I open the throttle the last 1/4 of the way it bogs noticeably and won't pick up. If I back off the throttle a bit the power comes back on. Seems like a bad lean bog once the secondaries open up. I've not done much with Quadrajets so not sure how to proceed. Any thoughts? Perhaps secondary air valve adjustment?

Other option is to forget the Quadrajet and go with something like an Edelbrock Performer and a Holley. Thoughts?

 

[jp89bayliner]

Re: Quadrajet issues... Help?

I just went threw the same thing this season. I down loaded a manuel off the www.carcraft.com about the quadrajet. I went threw mine with a carb kit I got at napa. After going threw it and putting jb weld on the bowl plugs was alot better.

I also soaked mine in carb dip for a 24 hours before the rebuild. I had pluged jets and the needle was not sitting in the jets correctly. I also replaced the power valve spring and now throttle is more crisp and has a ton more top end. Hope some of this helps. The quad is a good carb just need to know how to work on them and adjust them.

 

[mthieme]

Re: Quadrajet issues... Help?

It's the accelerator pump inside the carb causing the bogging.
Take it off, take it apart, clean it, throw in a kit.
When you put your idle screws back in, lightly seat them, then back out 2 turns. This should put them in the ball park. After running a few hours, recheck adjustment.
I have to freshen mine about every 4-5 years due to the same issue.
Matter of fact, I now have a spare on the bench to speed up the process.

 

[cadunkle]

Re: Quadrajet issues... Help?

I doubt it's the accelerator pump. When working the throttle by hand the accelerator pump shoots a nice stream down each primary venturi. Accelerator pump should have no effect on secondaries as it does not shoot down the secondary barrels, and at 3/4 to full throttle there is very little movement on the pump arm. Also the holeshot with this boat is real nice. Nail the gas and it revs up quick and goes. Actually feels like it's spinning the prop a bit before it grabs.

The secondary air valve is supposed to enrich the secondary side by ensuring a good pressure drop to suck fuel from the bowl, then make the transition to full open and secondary jets smoothly. I suspect that is where the problem may lie.

Perhaps the best thing to do is just rebuild the darned thing to ensure it's all clean and proper, then troubleshoot from there.

 

[Fishermark]

Re: Quadrajet issues... Help?

Perhaps the best thing to do is just rebuild the darned thing to ensure it's all clean and proper, then troubleshoot from there.

Sounds like a plan!

When you do be sure to epoxy the fuel bowl plug.

 

[MikDee]

Re: Quadrajet issues... Help?

FYI: If the engine ever backfired it in all probability ruined the power circuit diaphram.

This doesn't usually happen to a Qjet, a Holley maybe?

Anyway as the orig. poster said, the boat is new to him, it sounds like fuel starvation, it could be anything from the fuel pickup in the tank, the antisiphon valve, fuel lines, fuel filter, or carb fuel filter, once they are all checked, we can proceed from there.

 

[John_S]

Re: Quadrajet issues... Help?

FYI: If the engine ever backfired it in all probability ruined the power circuit diaphram.

I think you are refering to old Holley carbs. Q-jets have a power piston, but maybe you are refering to something else???




As stated above, I would try a clean and rebuild kit, and paying close attention to the air valve spring wind-up adjustment. Also, epoxy the well plugs.

 

[mthieme]

Re: Quadrajet issues... Help?

I doubt it's the accelerator pump. When working the throttle by hand the accelerator pump shoots a nice stream down each primary venturi. Accelerator pump should have no effect on secondaries as it does not shoot down the secondary barrels, and at 3/4 to full throttle there is very little movement on the pump arm. Also the holeshot with this boat is real nice. Nail the gas and it revs up quick and goes. Actually feels like it's spinning the prop a bit before it grabs.

The secondary air valve is supposed to enrich the secondary side by ensuring a good pressure drop to suck fuel from the bowl, then make the transition to full open and secondary jets smoothly. I suspect that is where the problem may lie.

Perhaps the best thing to do is just rebuild the darned thing to ensure it's all clean and proper, then troubleshoot from there.

Yep, that rules out the accelerator pump.
Sounds like you know more than you originally let on.
But, I agree - just rebuild the darn thing.

 

[LemmyAce]

Re: Quadrajet issues... Help?

No expert but I had the same issue with my Quadrajet it turned out to be the secondary needle (secondary metering rod) port side fell off the hanger and wouldnt lift.

worth a try.
http://www.carcraft.com/howto/57178/photo_14.html

 

[jp89bayliner]

Re: Quadrajet issues... Help?

No expert but I had the same issue with my Quadrajet it turned out to be the secondary needle (secondary metering rod) port side fell off the hanger and wouldnt lift.

worth a try.
http://www.carcraft.com/howto/57178/photo_14.html

That is the same one I was talking about above that is a good tech article!