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dirtking

Pilot screw

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I have a Zip-Ty fuel screw and it makes adjustment much easier I would say go with the Zip-Ty. I have not used the Pro-circuit one but if it is like the Zip-Ty it will be a lot better; because you can better tell where the fuel screw is adjusted as well as adjusting it without a screw driver.

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I've found the fuel screw on the YZ450 a bit tricky to get adjusted right 'cause it still backfires on deceleration when the screw's adjusted properly, but it must just be a Yammy design thing, and I turn it out a bit more for sand riding('cause the engine works harder and gets hotter). http://www.motocrossactionmag.com/me2/dirmod.asp?sid=&nm=&type=news&mod=News&mid=9A02E3B96F2A415ABC72CB5F516B4C10&tier=3&nid=6E5BCFD99FD242B28032722A4D5D52E3

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Ben,

If you're still running the stock pilot jet, try bumping it to a 45. Your decel pop will go away and your off-idle throttle response will improve. (this assuming you don't have an air leak in the exhaust )

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Right now I'm at a 48 pilot, 165 main and stock needle on the 4th (stock) position, with the fuel screw out 1-3/4 turns. The fuel screw on this bike is pretty well hidden whereas my Honda was visible. I installed an MSR fuel screw and it makes fuel screw adjustments much easier.

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I've done the searches a couple times before but I don't think I really ever understood the need for the adjustable screw. I believe I realize the fuel can be adjusted to provide a richer or leaner condition.

How does this relate to heat, cold, humidity or other conditions?

How do I know when an adjustment is necessary?

I pulled my carb apart about a month ago to do a cleaning. While I was at it I installed the JD Jetting kit, the Stealth accelerator pump and the Stealth fuel screw. The bike is running awesome but I haven't possibly encountered enough conditions to know when I need to make the fuel screw adjustments.

Thanks!

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I've done the searches a couple times before but I don't think I really ever understood the need for the adjustable screw. I believe I realize the fuel can be adjusted to provide a richer or leaner condition.

How does this relate to heat, cold, humidity or other conditions?

How do I know when an adjustment is necessary?

I pulled my carb apart about a month ago to do a cleaning. While I was at it I installed the JD Jetting kit, the Stealth accelerator pump and the Stealth fuel screw. The bike is running awesome but I haven't possibly encountered enough conditions to know when I need to make the fuel screw adjustments.

Thanks!

The fuel screw just adds an adjustment to fine tune the pilot/idle circuit of the carb. It is especially helpful in tuning throttle response. The idle circuit on these bikes is pretty sensitive so having the adjustable fuel screw is a must. Same goes for the needle. It's all fine tuning. Hotter weather, higher humidity and higher altitudes require leaner jetting and the opposite goes for richer jetting. The denser the air charge, the more air is taken into the motor thus the more fuel is needed to keep air/fuel ratios where they should be.

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Ben,

If you're still running the stock pilot jet, try bumping it to a 45. Your decel pop will go away and your off-idle throttle response will improve. (this assuming you don't have an air leak in the exhaust )

Nah, I'm just above sea level so I'm already using a #48 but will switch to a #45 when summer hits. I changed the pilot, needle position and main jet after the first ride because the backfiring with the #42 was crazy; something I wasn't used to with the KTM525 anyway.

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Check the slide on the carb, the hole should be down. I had same issue and was up to a #50 pj, fixed the slide added the JD kit and no pop and awsome power throughout the range, with a 45 pj, thinking of dropping to a 42 when leg heals

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