advice needed on a yz450f 2003

[killer454]

ok guys you have helped me get my nephews bike running good now i need advice on my bike.
i purchased an 03 yz450f about 4 weeks ago and bought it from a shop,the owner said it had the head redone with 5 new oem valves.i can see it has brand new gaskets on it.

my manual says run 95 or higher octain just curious what everybody is running in these bikes?

i pulled the plug the other day and it was black but not wet.

it had a gytr performance exhaust when i bought it,but i whent to repack it and found it had the core broke off inside.
so i bought a LEXX MXE slip-on from rocky mountain.
i have also installed that ice antifreeze,new oil and filter,new 10.00 spark plug.

it backfires on deceleration a few times but im seeing that this is normal for this bike i do beleave.
*do you have to rejet if you take the quiet core out or put it in?
this bike runs very good and it is scary powerfull for somebody that rode a 1979 it400 years ago.

thanks guys for the help and advice

 

[Matt90GT]

first off you need to read the octane recommendations. There is a RON and another index. Basically use premium gas in the bike.

plugs are a CR8e. Inexpensive. If you get a CR8EIX that is an iridium. those get about $10 a plug

For mods on the bike, well you have a new exhaust and popping. Inspect for ANY leaks in the exhaust system, any cracks in the header.

For jetting, we usually went up 1 on the pilot jet. Then installed an adjustable fuel screw to tune as needed with weather. Install a set of the TC forks from a 05+bike also. You will need the clamps and front axle also. Other than that, those bikes are a beast powerwise stock. They just dont handle like an aluminum frame model.