thermoquad wont idle down

[sweatybetty]

Its sitting on a 426 with a manual transmission, carb # 9379S
Rebuilt with all adjustments by the paperwork. Drove it 30 miles yesterday, runs great, mixtures on AFR gauge are all good. The problem is that the primary plates are completely closed (touching the bore walls, idle transfer slot not visible) and its still idling at 850-900, wont come down any lower. AFR reading 13.8-14.2 at idle. Mixture screws are out 1 3/4 turns. Fast idle screw full out. Choke wide open. I sprayed starting fluid around the throttle shafts, no noticeable change.
Pulled it apart and re-sprayed all the passages with cleaner, checked and double checked. Nothing amiss that I can see. No change.
There is no visible fuel when looking down the primaries.
Any advice would be appreciated.

Thanks all

 

[413]

Find your vacuum leak. That's the way enough air can be getting in to run it 900 rpm.

 

[sweatybetty]

I have pinched off the brake booster and pcv lines. No change. Ill try some more spray.
Thanks

 

[413]

Try something different. You've already sprayed. A throttle shaft leak won't pass enough ar to run at 900 RPM.

Cover the top of the carb, or close the choke, does it change the RPM or the way it runs?


Disconnect those lines and plug them. There is a problem and since we are not there you will need to figure it out.

 

[sweatybetty]

Closing the choke almost fully raises the rpm slightly. Closing completely kills the engine

 

[413]

Was the engine cold or had some heat in it when you did that test?

 

[sweatybetty]

Maybe 10 minutes after cold start.

 

[RustyRatRod]

Check that the secondaries are fully closed while running.

 

[sweatybetty]

Secondaries fully closed

 

[GTX JOHN]

x

 

[RustyRatRod]

Secondaries fully closed

Where is the vacuum advance attached? Is it getting manifold vacuum?

 

[Bewy]

Some 9000 series TQs had bypass air. On each pri throttle bore. A hole is drilled at an angle in the air horn to intersect the two front screw holes; these two holes in the black body are enlarged compared to the other holes. The air exits under the base plate. This was done this way to prevent nozzle drip. Block the holes in the base plate.

 

[Kendog 170]

Did you spray around the intake manifold?

 

[RustyRatRod]

Secondaries fully closed

Did you try to close them with a small pair of pliers WHILE RUNNING?

 

[sweatybetty]

Mechanical advance
I didnt spray the manifold. Engine was running fine with the Holley carb
Secondaries snugly closed running or not

 

[sweatybetty]

Ill pull it and check for the bypass holes.
Thanks to all of you!

 

[Mattax]

Timing at 850-80 rpm?

 

[Swinger 340]

Mechanical advance
I didnt spray the manifold. Engine was running fine with the Holley carb
Secondaries snugly closed running or not

The Thermoquads are known to crack. Possibly a vac leak at the base housing.