Hello,
Drivers side mix screw has no effect on carb.
Passenger side screw affects engine , I can run it all the
way in and stall motor. Right now turned out about 3 turns.
Vac reads 17-18.
Any ideas for drivers screw?
Both screws balanced at 3 turns out.
Carb is a 1970 era quadrajet.
It has been rebuilt by unknown builder.
Thanks
Marshal

 

Get a can of carb cleaner and give the air bleeds a shot. When the bleeds are blocked, the carb goes dead rich and makes the mixture screws insensitive. It has the same affect as fuel leaking into the manifold. Start with the idle air bleed on the affected side to see if that addresses the issue. If it does, then do the rest. If it doesn't, then either the bleed is still blocked or you have an issue of fuel control on that side of the idle circuit.

 

Or, you can check to see if the right-side intake gasket is leaking air into the intake. Shoot little puffs of carb cleaner at areas around that intake gasket while the engine is running, if the engine revs a bit, the area you just shot has a leak and is sucking in air.

 

Thank you
Gerry 72 and 7T1 vette,
I'll try suggested methods and report back.
Marshal

 

Gerry72,
I got a can of carb cleaner today and flushed out both idle air circuits.
The passenger side one I was able to flood and stall the engine.
The drivers side the curb idle raised when shot with cleaner but no
improvement. I could have emptied the can in this side with no effect except idle raises a little.
I was able to completely remove the drivers side mixture screw while the car was running with no effect on the idle.
I also loaded up the drivers side mixture screw opening with carb cleaner no improvement.
I lastly took a fine wire guitar string and sent it down both idle circuit
passages. It went down equal distance in length.
I did not force it to puncture anything just hoping to clear a blocked opening.
Still nothing
Passenger side mix screw out 2 turns vac reading 17.
Drivers out same but not able to effect any change when turned.
Also drivers side has a slight fuel drip into the opening as you said would happen. Passenger side does not drip.
Accelerator does give both sides a good shot of fuel when activated.
I'm out of ideas?
Thanks,
Marshal

 

Read a copy of Lars' paper "problems with rebuilt qjets". There's no way of telling what the problem(s) is until you open it up.

 

No carb pro by any means, but mine had a blown power valve from a backfire from timing being off. A/F adjustment screws could be all the way in an motor still ran. good luck.

 

you mite need a new gasket between the carb and the intake also .what are your idle rpms ?

 

From where is the fuel dripping?

 

The idle mixture screw holes shouldn't get too plugged, they're rather large. What I suspect is that the upstream passages are blocked, this is the idle down channel restriction and the idle fuel tubes. They are inside the carb on either side of the float bowl. They are frequently ignored during rebuilds and can get gummed up. The idle fuel tube is usually around 0.031-0.034" on a stock rebuild and DCRs in the 0.040s.

I just marked up this picture for you of a carb I worked on last year to help explain.

 

If the idle increased when you shot little puffs of carb cleaner at the intake manifold joints, then you have an air leak at those points. It sucked-in the carb cleaner and the added 'fuel' caused the rpm's to increase. If there were no air leakage, the idle speed could not have increased.

And, if you have an air leak into the intake manifold, then you won't be able to use the idle adjustment screws to make fine-tune adjustments...there's already too much are getting into the manifold for the idle screws to cut off. Fix your intake manifold leaks and you should be able to use the idle screws as intended.

 

Gentlemen,
Thanks for the responses.
I have no air leak between the carb base/gasket and manifold. Gaskets are approx. 1 yr old only and all 4 mounting screws were torqued evenly.
On the 427/390 I have the SS metal gasket against the manifold than the gasket as Lars directs on these engines.
The idle is set at 800 rpms.
The idle increased when I shot carb cleaner down the idle cicuit tube on the drivers side.
Like I said the passenger side stalled when shot with too much carb cleaner.
Also passenger mixture screw when ran all the way in will stall the car.
The drivers side circuit is completely unaffected by what ever I do.
Thanks Shark racer for the pic it helped me to see what it looks like beneath the air horn.
I have never taken apart a q-jet and was optimistic about clearing this blockage with out extensively diassembling the carb.
I can remove and sent to Lars at end of driving season in the fall if all else fails and I know it will be made right.

He's going to get it anyway I think but thought I might enjoy it throughout the summer first.
The fuel is dripping inside the ventri just below the butterfly you can see it being sucked in via vac.
The passenger side I was not able to detect this it seems like something is blocked so the fuel is rising and flowing into the ventri?
Marshal

 

If your manifold has the 'Smiley face" heat crossover, you must use three pieces to seal the carb to the manifold. Gasket (Felpro 60043), metal spacer, then Mr Gasket 4256G. I couldn't determine from your post whether or not you have the bottom gasket installed below the metal spacer.

 

JNB5101,
Sorry, my bust it does have the three gasket setup per an inquiry I made to Lars via email.
I have a new and correct bimetallic choke coil , non electric, and have deleted the heat riser in the pass. exhaust manifold by placing the correct spacer w/ gasket set up.
This car won't be driven after the temps drop in the fall in Penna.
I would love to get this idle circuit issue resolved although suprisingly enough, probably due to its inherit design, the carb runs fairly well otherwise.
I can zero to 80 progressively with the primary transitioning over to the secondaries nicely.
I was having WOT stomp issues but I think the new replacement ignition coil solved this.
I still have to confirm.
She was falling flat after 4 grand. I think the coil being an orig. item was not up to the task any more.
Some how I'll get it resolved even if I have to drive it like this in rich condition through out the season and send it to Lars in the fall.
Marshal

 

If the fuel is dripping out of the booster (Kind of hard to tell precisely from your description, but if you are referring to the choke plate as the butterfly, the boosters just below the choke plate in the venturi entrance) then you have a blockage in the high speed air bleed. The alternative could be a float issue, but that would tend to drip fuel from both boosters unless the float is just a wee bit high and you have a slight restriction in the air bleed on that one side. A perfect storm scenario, if you will. The reason the idle circuit is unresponsive to adjustment is the unmetered fuel dripping into the system.

 

Gerry72,
Yes it is doing exactly what you described in proper terms.
I just didn't know the names of the parts.
But yes the drivers side booster is just dripping into the carb.
Passenger side does not.
Whats the fix?
Marshal

 

A very thorough cleaning of all the passages is the only fix. If you are going to be sending the carburetor off to Lars, it's something he will pay attention to. You could clean the carb yourself, but if this is an area where you have no experience, you may not be effective.

 

Gerry72,
Ultimately I think you are correct and I will enjoy the driving season ahead and fall time send the carb off to Lars.
I could fiddle fart around all summer untrained and more than likely never correct the problem.
Thanks for the proper diagnosis though.
Marshal