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It's starting to get warm up here in upstate new york and im wondering if i need to go up on my jets. It runs good wide open but when i let off the gas it back fires alot. more and more as it gets warmer. i think it must be running lean becuase the motor is running alot hotter and the bad air factor, BUT when im going in low RPM's and the motor goes under load like goin up a slight upgrade it feels like its loading up with fuel like its stalling. Which i dont know if its lean or rich. it seems to be rich. but i dont want to go down on jets becuase its backfireing. ANY ideas?? do you think when it bogs down it might be a lean condition? thanks in advance.

PS- i have 25 pilot-3 1/4 turns out, needles in middle, and 170-175 mains(alright)

HMF full exhaust and no lid on airbox with K&N filter
 

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Hotter temps means thinner air = less fuel.

Colder temps more dense air wich requires more fuel.

You could be lean on the pilot circut causing the backfiring when you let off the throttle. It isnt from it getting warmer though. Probably from the pilot jets being dirty wich restrict fuel flow, leaning your mixture out.
 

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Discussion Starter #3
ok, ill check it out sometime. if there not dirty then i will put in the 27.5 with 1.5 turns out and try that. But do you think the bogging in low rpms under pressure is a lean state?
 

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so it used to run good? if its been sitting for a while i would pull the carbs off and clean them real good and make sure everything looks good, i think you have dirty pilot jet(s) and maybe your float valve is sticking or needs replaced.....i dont know for sure, im still new to 660's, but thats what i would do first, and maybe change the sparkplug and check connections
 
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