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angrybob

'06 YZ450 Jetting Question

5 posts in this topic

Right now my bike runs great at 1500-3000 feet. I have a 165 main jet and a 50 pilot jet. This Saturday I will be riding between 8000-10,000 feet. I have the ZipTy fuel screw at 3 turns out. Is there enough adjustment to choke off enough fuel in the pilot circuit to leave it alone? I am thinking that I should drop to a 45 pilot if not. What about the main jet? The guy I'm riding with has a CRF 450 that he drops 5 sizes on the main. That would put me at 152. Does that sound right? Needle is in the stock position. Does that need to change?

Any help would be appreciated.

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To correct for a net increase in altitude of 7000 ft, multiply your jet size by .94. That comes out 154, so a 155 should be right.

I cannot believe your bike runs well at all with such a rich idle circuit, however. Both my '06's run great at altitudes between sea level - 4000 ft with a 45 at about 1.75 - 2 turns out.

Either way, try the 45 for this trip. Needle will probably be alright.

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Thanks for the info...where does the 0.94 come from?

I was surprised too. Its a first kick machine with moderate backfire on off throttle engine braking.

My pilot jetting steps are here.

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155 main and 45 pilot worked great today. Not perfect, but good enough. Just because...I'm going to leave the 45 pilot in and see how it runs.

I bought the bike used, but I was never told that there was any flow / head work improvements. I cannot understand why the 50 pilot works either.

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