Choke and Fast Idle Relationship

[thumper]

Hi Cliff and guys.
I want to adjust the fast idle on my carb to 1200 rpm or so. When I dial back the fast idle screw, the truck doesn't want to start. So I am missing something.
The setup on the choke is frustrating as a lot of times the unit wants to do its job when it is really not needed. I want more control of the choke!
Any suggestions are appreciated!
Thanks, Thumper

[429bbf]

thumper give us an idea what carb and rig your working on.is it electric,hotair or manifold controled.dean

[73 Z28]

Knowing what kind of choke setup will help understand what is happening. Normally a good cold start fast idle speed should be about 1600-1800 rpms. Once the choke comes off of the steps of the fast idle cam it should reduce to about 1000-1100 rpms in neutral or park. Has your carb been rebuilt?

Paul

[Cliff Ruggles]

What is the carburetor number and application?......Cliff

[thumper]

What is the carburetor number and application?......Cliff

Sorry for the delay.
Carb # is 17057512 1867. 463 BBC with hot air tube in manifold. Carb is a Cliff Ruggles rebuild and works great!
Thanks for the replies. Thumper

[Cliff Ruggles]

Hot air chokes are very reliable, as long as the intake gaskets aren't blocked off.  They provide a lot of heat to the choke tubes, so they open quickly. 

It may take several attempts to find the ideal position for the choke, choke pull-off, and fast idle speed adjustment.  You have to work quickly on a dead cold engine to make accurate settings. 

Best to set the dial so it just barely closes the choke flap on a cold engine, and use this as the "base" setting.  The choke flap should snap shut on a cold start, and be fully open within 3 minutes.  Turning the dial to the right (clockwise) shortens opening time, to the left makes it stay on longer.  If you turn the dial too far to the right, the choke flap doesn't fully close, making the engine more difficult to get started when cold.....Cliff

[thumper]

Hot air chokes are very reliable, as long as the intake gaskets aren't blocked off.  They provide a lot of heat to the choke tubes, so they open quickly. 

It may take several attempts to find the ideal position for the choke, choke pull-off, and fast idle speed adjustment.  You have to work quickly on a dead cold engine to make accurate settings. 

Best to set the dial so it just barely closes the choke flap on a cold engine, and use this as the "base" setting.  The choke flap should snap shut on a cold start, and be fully open within 3 minutes.  Turning the dial to the right (clockwise) shortens opening time, to the left makes it stay on longer.  If you turn the dial too far to the right, the choke flap doesn't fully close, making the engine more difficult to get started when cold.....Cliff

[thumper]

Thanks Cliff!
I shortened opening time and will start there. Choke has been holding on too long for my taste. For now I'll keep the fast idle at the factory recommended 1600 rpm.
With the fast idle always wanting to engage, a roller in the transmission takes a beating with a band.
What are the options for the choke pull off settings?
Thanks again for a great rebuild. I am starting to get some dark greasy spots on the front of the carb. Should I consider some gaskets...?

Thumper

[Cliff Ruggles]

The rule of thumb on the pull-off is to set it so it unloads the choke and the engine runs smooth on the first cold start attempt.  Best to er on the lean side just a bit (flap open further), as it is better than having the flap too far shut and "washing" down the engine. 

The choke should be fully open in about 2-3 minutes, and has a wide range of adjustment.....Cliff