1971 FJ40 carb adjustment

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Mar 4, 2014
I just installed a OEM rebuilt carb. It seems to work great. I'm having trouble understanding all the adjustments. Read the F-engine and Haynes books. Too many carb models in the same book. Anyway I figured there must be a carb expert out there who brain I can pick.
I have located the idle mixture screw.
There are 2 other adjusting screws on the opposite side. I guess the idle throttle screw and the high idle screw. I turn either one and I can't get my idle to raise up.
With my choke pulled half way out, it runs fine. When I put the choke all the way in, the engine wants to stall. Easy problem if I can figure what I am missing.
It's a February 1971 model.
The first thing I would recommend is to make sure that your idle solenoid is working and is energized. Listen for a click when you connect/disconnect the wire. If that's not working, that could cause your symptoms.
The second thing I would do is to make absolutely sure that you know what each screw is/does before you start screwing around (no pun intended).
The idle mixture screw is in the carb base. I would start by screwing that in CAREFULLY until it bottoms out and then back out 3 turns.
You should be able to determine the fast idle speed from the idle speed by looking at them and seeing what they control:
With the engine off, step on the gas and pull out the choke. Let the gas off and go look at the carb. Pull on the throttle linkage and look at the screws. One of those two screws will be hitting the linkage and will be controlling how far the linkage can return. That's the fast idle speed screw. Now, push the choke in and operate the throttle linkage while looking at the screws. The OTHER screw should now be controlling how far the linkage can return. That is the idle speed screw.
With the choke on, the fast idle speed screw should control the engine speed. With the choke off (which you can't achieve) the idle speed screw should adjust the idle speed. Only one of them should control the engine speed at a time-depending on the choke position.

Start the engine with the choke on and let the engine warm up. Push the choke in slowly, the engine speed should drop slowly until the idle speed screw is touching the linkage. Look at it. If the idle speed screw needs to be screwed in to keep the idle to 6-700 RPM, do that. If the engine wants to stall out and you need to crank the RPM up higher to keep it running, do that. If you have to do the latter, you find yourself in the common position that the problem is probably not in the carb. I'd start by looking for vacuum leaks (or possibly something ignition related since you didn't say anything about the condition of the rest of the engine).

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