[Fullback66]

I need some help on my tri-power.

When I start up my 66 GTO the RPMs want to jump to about 2500-3000.

I can get out and move the fast Idle and choke trip lever to bring the RPMs back down until the car warms up.

After that it is fine. Until it cools down again.

Questions:
Why is this happening?
Is there any thing I can do without taking off the carb?
What is the fix even if I have to take off the carb?

Thanks guys
FB66

[Dick Boneske]

Startup rpm with the choke engaged should be about 1500-2000 rpm. This is controlled entirely by the fast idle cam, choke pull-off diaphragm, and setting of the choke rod on the passenger side for a '66 Tripower like yours. I agree 2500 to 3000 rpm at start is too high.

Remember, this is a carburetor, not fuel injection. All of the comments below apply to a single 2 barrel engine after 1967 as well as the '66 Tripower. You need to tap the accelerator pedal to engage the choke before startup and AGAIN immediately after startup to drop the idle speed. The fast idle cam cannot move unless the throttle is opened--just a tap on the pedal will work.

On cold startup, the choke pull-off diaphragm will open the choke slightly and drop the fast idle cam to a lower rpm if you tap the throttle immediately after startup. The amount the choke is pulled open on startup is determined by how much you bend the small rod from the diaphragm to the top choke lever. The correct setting is 5/32" choke opening when the diaphragm is fully retracted. Bending the small pull-off rod will increase this opening if you want to experiment.

The rod that extends from the choke stove in the manifold to the choke lever can also be bent to shorten it. This will result in less spring pressure on the choke mechanism. The factory setting is to disengage the rod from the lever on the airhorn and bend the rod until it fits in the small detent in that lever. If you bend it more to shorten it, the choke will open faster as the choke coil heats. The choke should close completely when you tap the throttle with the engine cold and not running.

If you're not able to accomplish cold startup performance as you want it, a last resort would be grinding some material off the fast idle cam step that the idle rpm screw contacts when the engine is shut off and the choke is closed. You can mark that step on the cam, remove the cam, and grind material off. Just remember, don't remove too much--a new fast idle cam would be the only fix for that.

None of the above requires removing the center carb. If you need pictures, I'll post some showing the details of these adjustments.

[Fullback66]

Mr.Boneske

Thank you for the great information. I would like to see a few diagrams if you do not mind.
Why would it just start doing that? Is there dirt in there? So weird.

Thanks
FB66

[Dick Boneske]

Here is a diagram of the choke pull-off and the choke rod from the choke stove.

[Fullback66]

thanks,
I will give it a try.
FB66