Quadra-jet carb problems

[westzoo]

I have a 1979 260hp OMC that wants to get back into the water after a long dry spell. I rebuilt the Rochester Q-jet and replaced the secondary metering rods that were bent. It seems to run OK with no load but in gear I have to keep goosing the throttle to keep it from stalling. Not good in a no wake zone! The idle mixture adjustment screws have no affect on the way it runs whether they are open 6 turns or completely closed. Has anybody had an issue like this? Somehow fuel is still getting through the carb at idle even when the mixture screws are closed. Is it possible that the carb was metered for high altitude (came from Lake Tahoe and is now in the AZ desert). Also runs a little rough at WOT but seems to run better when choke is held partially closed manually so it must be running lean. Maybe the primary metering rods are damaged too. Could that cause the issue with the mixture adjustment screws? Any Quadra-mechs out there?

 

[mkast]

Re: Quadra-jet carb problems

Sounds like a vacuum leak.

 

[dan t.]

Re: Quadra-jet carb problems

how did you clean the carb? spray cleaner is a waist of time, it sounds like some of the small passages called air bleeds are plugged. strip it down and take it to a shop that has imersion cleaner and get them to soak it overnight then blow it out with air. run a small wire such as is found in a wire brush thru all the air bleed holes and blow them out again
good luck

 

[westzoo]

Re: Quadra-jet carb problems

I did soak all parts of the carb in carb cleaner, used assorted wire brushes and toothbrushes etc., then rinsed with water and blew out with compressed air. I am pretty sure that all passages were clear. I had a Q-jet on the '68 GTO I played with in my younger years and rebuilt that one without issues, It ran like a beast! Have checked the obvious hoses and connections for vacuum leaks but didn't check all of the intake manifold to head connections. Will check that next time I fire it up.

 

[westzoo]

Re: Quadra-jet carb problems

Still curious whether anybody else has encountered this issue with the Quadra-jet carb where the mixture adjustment screws don't affect the idle. I am thinking maybe the power piston spring could be shot or the primary metering rods or jets or something. Just looking for suggestions. Does anybody know what size the factory metering rods and jets were in this carb? Rochester #17059286 on a 1979 OMC 350, 260hp. If I knew I was at OEM settings I would feel better about trying to tweak it from there. Thanks for any help.

 

[westzoo]

Re: Quadra-jet carb problems

BTW, I checked for vacuum leaks with starting fluid all around the intake manifold and around the vacuum fittings and carb and did not detect anything. Thank you again for any help.

 

[dan t.]

Re: Quadra-jet carb problems

primary jets 70
primary rods 44
secondary rods dv
secondary hanger f
power valve spring hight 1.022

as I said before,check the air bleed tubes, they are the little brass inserts on the front side of the venturi, they can plug very easly, make sure you have the correct gasket between the base and the center section

 

[remauto1187]

Re: Quadra-jet carb problems

Did you replace the throttle and butterfly shaft bushings? If not then that is your problem. They are leaking air into your carb which is leaning out your mixture. Check the spark plugs after running the boat. This is a common problem that is overlooked when rebuilding rochesters.

 

[dan t.]

Re: Quadra-jet carb problems

unless the throttle shaft is extremely worn this is not the problem, a worn shaft can give you an inconsistant idle speed due to the butterfly hanging up in the bore. you will still get a response from the idle mixture screws

 

[westzoo]

Re: Quadra-jet carb problems

Thanks dan t. very much for the quality information. I am going to check to see what the primary jets and metering rods are and am curious about the spring too. I know the secondary is correct. Gonna take another look at those shaft bushings too but if they were worn I think I would have detected a vacuum leak around the base of the carb wouldn't I? Will post a progress report as progress occurs. Unfortunately the closest body of water for testing is about 90 minutes and half a tank of gas away.