I got my new Duncan exhaust and Pro Design intake with the Uni foam filter no lid installed on my 06 yfz. Rejetted with the following- pilot jet 45, main jet 180, stock needle (non adjustable) and tinkered with the fuel mixture screw and it ran like shizz!!! Very boggy at 1/4 to 1/2 throttle kept dying if I wasnt on the gas. Header glows bright red at night shooting the hill (throttle pinned). Header glows at idle also. When I rev high it seems to backfire. Our elevation at the Dunes is approx 4800 ft above sea level and the temp was about 36 deg all day. So whats up ? any and all advice will be very appreciated.

 

Sounds like alot of lean symptoms, youre gonna need to go bigger on the main jet. Try a running with the lid back on the air box, if it improves, then youll know for sure its too lean.

 

Ill try the lid back on> I was wondering about the needle should I throw in an adjustable one?

 

You should be able to shim the needle if it needs it, wait and see how it runs, when you get the main jet correct.

Heres a good article on jetting, and at the end of it, theres a list of symptoms of lean and rich, which may help figure out which way you need to go.
jetting

 

Get a stock needle for the YZ 450 F, do a search on the part # I would also get a Zip-ty to replace the idle mix. screw. 180 on the main seems a bit rich for that elevation.

 

NCVQ Needle #5TA-14916-V1-00 that is the OEM YAMAHA part number........
Your 180 Main is to rich for that alt. try going to a 168 or 170.......Good luck [img]i/expressions/face-icon-small-smile.gif[/img]

 

Does it idle ok? If so leave the pilot alone..I would get the NCVQ needle the last guy suggested and try jetting down to a 175 or. turn the screw 2 turns out until you get the jetting closer and then adjust.

 

I got the dirt bike needle, gonna throw that in. As far as my main I've got a guy who helped me jet this who races in the pro class on a yfz hes got 2 of them and thats what hes runnin. Up top wide open it seems ok. Thanks for all the input.