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05 yfz 450...jetting issues


crprestridge
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just moved from sea level to about 4500 feet above see level. I already have a #170 jet in my carb...i finally got it to start after turning the fuel/air mixture screw a total of 5 1/2 turns out(it was running good at 2 turns out). gonna get a new jet and here's my question.....what size should i go up to? i'm trying to avoid buying a handful of different jets. and my next question is do you think i'll have to change my pilot?

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Dream Car Giveaway

You need to go down in size, not up. I would aquire all sizes from 160 to 170, you need to be able to adjust for temp changes. I would start at 165 and go from there. If you had to turn your screw out 5 1/2 turns just to get it to start, then your pilot jet is too rich. You will need to run a leaner pilot too. The engine should idle highest at 1 1/2 - 2 1/2 turns out, use a pilot that gives you that result. You will probably also want to move the needle clip up one spot. If you have to run it with the clip in the top spot, then you might try a needle with a leaner taper.

Edited by DirtDemon
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ok. i now have the pilot at 42(one size smaller), the needle is on the middle clip, and the main jet is 160(from 170). It idles fine and mid throttle is good. It still cuts out on topend(acts like water is in the gas, which i know is not the case). Do you think i still need smaller main? The bike ran crazy fast at sealevel with no trouble. i haven't adjusted the needle at all. What to do?

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Good to hear, I am suprised that a 168 main is doing it, but moving the needle may have helped. Also if it is alot colder there, the elevation will make less difference because the cold air has more oxygen in it, helps offset the high altitude. Either way, glad to hear you got it dialed in.

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  • 3 weeks later...

i didn't move the needle at all actually. i was just posting all settings in case anyone had the same circumstances in the future. all i did in the end was get some advice from local yamaha mechanic and went down one size (from my origianl sea level setup)for the pilot from 45 to 42 and one size for the main from 170 to 168. i had the main as low as 162 and on top it would get real lean and cut out bad. it's all good now though. thanks everybody for your imput. you guys are awesome and so very helpful. if ever in the ogden/ salt lake area, hit me up. i would love to ride with you guys. later. thanks again.

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