yfz450 jetting

[yfz450bk]

i have a yfz 450 and i live on the boarder of penn. in new york, i put a full hmf exhaust on and i put a 160 main from a 158...i left the pilot and fuel/air screw alone....i have an aftermarket air filter also...it runs good but when i let off it will back fire in small consistant pops and somtimes a big pop....i want to know if that matters or if i'm sacraficing any power and what i should do if i am

[mountaineer]

Keep going up on your main until you loose the pop. You are lean. DO NOT RUN YOUR QUAD IN THIS STATE. The quad will pop on deceleration when you are lean. I would also go up to a 45 pilot.

Try a 165 or 168 main, 45 pilot, and 1 1/2 on your fuel/air ( It should be there already from the factory).

Hope this helps I have a mechanic who is a guru with jetting and has let me know his secrets:D
If you have anymore questions give me a shout?

[yfz450bk]

thanks for the help man... thats what i thought to do but wasnt sure......i'll be sure to make those changes and let u know how it works out

[mountaineer]

Happy to help!

[Scooter86]

Hey, how did your jetting work out? I also have a full HMF, and had to go up to a 60 pilot and 175 main to get rid of the popping. Even then I feel it might be better yet a little richer. I am in western NY, so we should be pretty close in settings. I still run my lid also.

[dimnova36]

i also have a yfz that pops and sometimes backfires on a steep decel or if i downshift to slow down. Is this bad for the quad?

When i am on the throttle the things rips and it seems to have plenty of power and a nice smooth powerband. Is it possible i could be get more power from a larger main jet. When at speed it seems to run really smooth. its just on the decel that it pops.

and i also have a fmf pipe and k&N proflow filter

[yfz450bk]

i went up to a 165 main w/ a 45 pilot and it rarely ever back fires any more(it was too lean when it did)....w/ most aftermarket pipes it may back fire seldomly no matter what because of a lack of back pressure because the exhaust is so wide open....just try going up in your main and pilot sizes till it stops.....and be careful of your K&N filter because if you don't have a prefilter cover it wont stop the fine particles from being sucked in