The Mighty 258 > Fuel Systems.

What causes carb to move to fast idle position? Choke thermostat?

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86Woodgrain:
Hey all, I rebuilt the stock carb about a year ago, replaced all vacuum hoses, replaced choke pull-off and choke thermostat. Used factory Carter BBD service manuals and more to rebuild the carb and it was basically PERFECT at that time.

Fast forward to this year and it runs rough and rich while warming up and refuses to go into high idle position when I do the usual press it to the floor before starting. Now it is getting cold here, like -20 C so it's definitely cold.

I haven't researched a lot yet but is it the choke thermostat that causes the linkage to move to the fast idle position? If I can get it back to going onto fast idle at cold startup I think that will fix it. The choke thermostat was new last year and I put voltage to it to test it and it does move some. I don't know how far it should move though and how fast. I think I have about 60 seconds maybe for the choke thermostat to do it's job? Not sure.

I really need to get fast idle working because I have basically parked the car for the time being while I figure it out. It's OK it's not my daily driver, fortunately.

TheBirdman:
Yep, the choke thermostat pulls on a linkage that moves the choke plate, and a little cam that sticks under the throttle linkage, to bump it up for high idle. Theres some complicated adjustments you can make to adjust the fast idle separate from the choke, but the easiest thing to do is loosen the 3 screws around the ring that holds the choke thermostat on, then turn the thermostat so that it pulls the choke linkage further.

86Woodgrain:
Which way should I rotate it? I rotated it counter clockwise as you are facing it. I turned it until the choke was fully open when hot. I will test cold function tomorrow.

TheBirdman:
I forgot, but as you twist it either way, you will see the choke blade closing and opening. Go the direction that closes it more to give it more choke and fast idle.

86Woodgrain:
Then I turned it the wrong way.

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