COMET CENTRAL

I have a Summit Racing 600VS carb on my 302. The last few times that I have driven my car, I noticed that the engine came off fast idle late according to engine temperature (engine at 160 and still at 1400 RPM). I gun the engine, and RPM drops to curb idle, 900 RPM. But sometimes I gun the engine and it actually gains RPM after I back off the gas pedal, maybe to nearly 2000 RPM. Drive a mile or so, gun the engine a few times and then all is fine regarding being at curb idle when I stop the car.

With the engine cold, I removed the air cleaner and noticed that the choke plate was open. It should be closed, I believe. So, I assume that the fast idle cam is sticking. When I open the throttle, the cam drops out and the choke plate closes.

The motor fires up without hesitation.

Could my fast idle set screw be a bit too snug against the step-down cam?

Thanks in advance for comments and suggestions.

Jerry

Check the accelerator linkage for any binding or slop.
Are you using old stock bellcrank or has it been modified?

Joe

jarudd74 wrote: ↑

Tue Nov 08, 2022 4:02 pm

With the engine cold, I removed the air cleaner and noticed that the choke plate was open. It should be closed, I believe. So, I assume that the fast idle cam is sticking. When I open the throttle, the cam drops out and the choke plate closes.

The motor fires up without hesitation.

Jerry

THIS IS NORMAL to be open until you give it a pump of the accelerator . & is why you always press the gas pedal down once to set choke before starting it, & if it was driven the day or 2 -3 before,,, this one pump should give it a squirt of gas to help it start right up.
But your choke needs to be set so it just barely fully closed on a cold morning & not turned any more. ****But should always be fully open when motor is fully warmed up.

choke not set right will throw off the fast idle settings.Only after the choke is properly set can you adjust fast idle right if it needs it , but I would test it a couple mornings,,,get the choke right, before I changed fast idle.& cant be set with motor warm,so you only get one try per day. lol
Keep in mind these cars need to warm up completely before the choke & fast idle are no longer engaging.



there are little marks on the choke ,& depending where you live may need to be set a little different for winter & summer. some even have a little W & S at the ends of the setting marks. I'm sure summit has videos on how to set everything.
but knowing how a choke works will help. all it is is a coiled up thin piece of metal which contracts in the cold & expands in the heat. so as it warms up it opens the choke.

jarudd74 wrote: ↑

Tue Nov 08, 2022 4:02 pm

I gun the engine, and RPM drops to curb idle, 900 RPM. But sometimes I gun the engine and it actually gains RPM after I back off the gas pedal, maybe to nearly 2000 RPM. Drive a mile or so, gun the engine a few times and then all is fine regarding being at curb idle when I stop the car.

I'm referring to this one. Only problem I see.

Joe

Joe Travers wrote: ↑

Tue Nov 08, 2022 7:37 pm

Check the accelerator linkage for any binding or slop.
Are you using old stock bellcrank or has it been modified?

Joe

I am not sure of what a bellcrank linkage is. Excuse my ignorance.

The linkages move manually without any resistance that I can sense. Plus the linkage movement feels tight, not sloppy.

Thanks.

Bellcrank for accelerator linkage, mounts on intake manifold.
You can wiggle the top of the arm to see if the bracket is worn where the pivot rod rides (red arrows). Also check the bracket the pedal rod rides in that's mounted on the firewall. Mine rocks just a tad in both from wear over the years. Pedal feels good but there is a little free play in the linkage. Best way to check is get someone to press the pedal down in the car while you watch for any rocking motion on both.

Joe

Joe Travers wrote: ↑

Sat Nov 12, 2022 12:08 am

Bellcrank for accelerator linkage, mounts on intake manifold.
You can wiggle the top of the arm to see if the bracket is worn where the pivot rod rides (red arrows). Also check the bracket the pedal rod rides in that's mounted on the firewall. Mine rocks just a tad in both from wear over the years. Pedal feels good but there is a little free play in the linkage. Best way to check is get someone to press the pedal down in the car while you watch for any rocking motion on both.

Joe

Since my last note, temps in my area are down by 30 degrees. Took the Comet out today and the RPM (throttle) issue was more pronounced.

My linkage is different. I have slowly advanced the throttle without seeing any apparent sticking or sloppiness. That being written, would the linkage benefit from lubrication? If so, what type of lube to use? I am certain that the fast idle cam is a dry fit.

Thank you.

Hey Jerry,

Can you post a photo or two with your setup. That may help.

I had issues with the linkage causing binding in the butterfly plate. The linkage always appeared fine and lose, but when attached the other side was binding. I've also had issues with the vacuum advance sticking in the distributor and causing erratic idle (if you have that setup). I don't think there is any lube necessary for the linkage.

Just throwing some stuff at the wall here. If you've checked all of these than disregard.

Groover wrote: ↑

Wed Nov 23, 2022 8:17 am

Hey Jerry,

Can you post a photo or two with your setup. That may help.

I had issues with the linkage causing binding in the butterfly plate. The linkage always appeared fine and lose, but when attached the other side was binding. I've also had issues with the vacuum advance sticking in the distributor and causing erratic idle (if you have that setup). I don't think there is any lube necessary for the linkage.

Just throwing some stuff at the wall here. If you've checked all of these than disregard.

You might try loosening the base of the carb & test the throttle movement,then retighten. I've had butterflys bind because the carb was twisted a tad making them scrub.

On a carb car, it is a good idea to let the car warm up to where it is not operating on fast idle mode. It is even a good idea to let these modern FI cars warm up before we take off even though they will run fine Engine wear.