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Discussion Starter · #1 ·
Hey, I just can't seem to get my trail boss 250 to idle and run properly. I have eliminated the crank seals, and carb boot as the problem. I have tried 1 size smaller pilot jet, still no luck. While messing with the idle and air screw, it will idle too slow and almost stall or it will idle way too high. Tried moving the needle clip around as well and I just ant seem to get it. Any idea what's up?
 

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Use some WD-40 and spray around the carb,manifold,cyclinder base,with the quad running. It'll speed up when you find the air leak.
 

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Could be a bad air/fuel mixture screw. All it takes is to over tighten the screw into the carb. That could cause the adjustments to be really off.
 

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Sometimes , the little way on the slide develops a spot ,where you cannot get it to rest correctly on the idle screw, making it almost impossible to get it to idle at the speed you want it to.Try disassembling the carb. and check the slide,where the idle screw sets, you may have to fine file or emory cloth this area.
You do have to adjust the air mix screw, after the engine gets warmed uo and the air cleaner housing must be installed,Try at one turn out and see how that goes
 

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The air fuel should be out 1 1/2 turns for starters. The one your talking is not so critical. It still sounds like an air leak or the carb has the idle passage is dirty.
 

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Discussion Starter · #8 ·
I am very confident the carb is cleaned well. As for the air leak, that's what I think it is too but can't find one anywhere. There is also a very bad bog between idle and 1/4 which led me to believe it was the pilot aswel. It's only started this b.s. since I put the 1988 carb on it that I bought at a cycle salvage since the original was in very bad shape. I put a new pilot and main hex jet in it that was stock to the 90. Then I used the orig. needle jet, throttle valve, and jet needle to the 1990.
 

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Stock Polaris 250 carbs are a dime a dozen. I would find another used on and try it. If it still does the same thing and your carb boot is good then it HAS TO BE an air leak in the engine. If that is the case you mays well pull it out and put all new gaskets and seals in it and freshen up that old girl!
 

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Discussion Starter · #10 ·
Update. Turns out the tb 250 carbs aren't common or cheap. I can get it to a point where it will idle but when u hit the gas, the rpm goes and stays up. Then I got to another point where i can rev it up an it will come back down like normal but it won't idle.
 
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