F 12 Carb adjustment

Craig45 · Nov 17, 2011

One of my F 12's is hard starting, runs rough and seems to flood out. Pulled the carb off and disassembled. Float arm is at 3/4 in. And needle valve shuts off. My book says that the main fuel valve should be set at 2 1/2 to 3 turns, however at this setting the hole metering fuel is completely open. Am I overlooking something? Thanks Craig

Bill in NJ · Nov 17, 2011

I'm assuming you are talking about the idle mixture screw. This screw adjusts the mixture at idle. Above idle it does nothing. That 2 1/2-3 turns is usually just a guessimate. With the engine running at idle, screw the idle mixture screw in until the engine sounds like it is starving for fuel. Then back it off about 1/4-1/2 turn. It should idle nicely there. If not, you more than likely have a problem with the float sticking or the needle valve not seating correctly.

Craig45 · Nov 17, 2011

I was talking about the main metering adjustment, it seems that the 2 1/2 to 3 turns leaves the hole in the tube completely open. I will reinstall and adjust it so that the hole in the tube is 1/2 closed by the adjusting screw and see what happens. craig

JRSutton · Nov 17, 2011

Those number-of-turns specs are meant ONLY to give you a "fool proof" setup to start the engine.

They're not intended to be LEFT at those settings. It's not abnormal to be off quite a bit from them by the time you're adjusted perfectly.

Especially with an old carb where people have been turning those screws in and out, mashing them up a bit at a time over the past 70 or 80 years.

If you're just trying to get the tractor to start, go by the numbers. Once it starts tune it to where it makes you happy. There is a chance they're too worn and you can't turn them in far enough to do anything, but it doesn't sound like you're there yet.

F 12 Carb adjustment

Craig45

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Bill in NJ

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Craig45

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JRSutton

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