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Old 04-10-2010, 06:29 PM
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Mikuni Carb

Hi I have a 85 trail boss 250 2 stroke with carb issues. it wont idle at low rpm but does run very good at higher rpms, im not sure if the parts inside are the right ones or not but i have tried a 40 and a 45 pilot jet but still no change if i am reading them correct i have tried a 145 and a 230 main jet the 230 was just an extra. also tried with and without breather box. also how far should the jet needle go into the main jet? should it touch bottom? any info for this would be greatly appreciated as i dont know much about these type of carbs. one more thing it seems the only way to get it to start is with choke on and cover the carb warm or cold no difference.

Last edited by tomc3976; 04-10-2010 at 06:37 PM.
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Old 08-24-2011, 09:55 AM
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Tom i don't know what elevation you are at. I am at 4880ft and i run a Main jet 130 and a 35 pilot also the #2 clip position from the top. are elevation set up is at 8k-10k
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Old 08-24-2011, 04:01 PM
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you should be running a 145 main jet for 0 to 3000 feet. and a 30 pilot jet,check the color of your sparkplug and adjust for color,start at 1 1/2 turns from fully seated[air screw],and make sure that your float level height is adjusted .last i would check the oil pump make sure the pump mark lines up with the pump lever mark.
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Old 08-25-2011, 03:41 AM
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I agree with mastermech. set it up to your elevation. I am curious do the 86 Polaris trail boss have a low oil sensor which will make it not idle???
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