750 QuickFuel Carb on a 427 electric choke on 351W

[MillerCobra]

Hi everyone, driving the car today something has come up with my carb. It at times has a slow return after letting off the throttle. So in-between shifts the engine stays at high RPM's and slowly drops down. Not a good thing. I stopped and got a spray bottle of carb cleaner and cleaned the moving parts but it did not make a difference. It does not happen every shift. To help I have to tap the throttle. The engine is a 351W that is bored to 427, mechanical fuel pump, MSD ignition, 750 QuickFuel carb. Just 4800 miles on the car. I have attached a vid of it moving. Nothing rubbing or binding the foot peddle or set up. Is it something with the choke? Going to the forum first.



https://youtu.be/G7Ar663onnU

[j.miller]

I'm sure you have checked your return springs....sounds like the primary venturies are hanging open.....elect choke may not be fully releasing after warming up.

[ThickCobra]

Thanks for the heads up. I believe I have the same set up and I'll be watching both of those items.

[NAZ]

Can you duplicate the problem with the engine at operating temp and without the engine running? Take the return springs off (but don't try to remove any springs integral with the carb -- just the typical linkage return springs) and check the throttle linkage and or cable for any binding -- it should be buttery smooth when operated by hand and should return to the idle position with only the carb butterfly shaft spring. If you feel any resistance in the linkage remove it from the carb and check the carb operation. If the sticking issue is not in the carb then you need to start systematically eliminating components in the throttle linkage system including the accelerator pedal. I have seen many worn carbs (or improperly assembled rebuilds) have sticky butterfly valves which usually only show up at WOT or at the idle closed positions. I've also seen the accelerator pedal pivot binding and even had one customer with the carpet hanging on the pedal and keeping it from returning to the idle position. And as j.miller stated above, the choke system can hold the throttle open and you can check this by using a 12VDC jumper to the electric choke on a cold non-running engine. The heating element takes several minutes to open the choke and once it is opened a quick blip of the throttle should result in the fast idle cam disengaging allowing the throttle to return to the normal idle position.

[MillerCobra]

Thanks everyone. NAZ I will work your procedure to see if I can find the problem tomorrow.This forum is so valuable for troubleshooting, again thanks.