Hesitation off idle to WOT

[acesfull]

I just got my initial break in done for 10 hours on my brand new YFZ450. It was hard not getting on it for that long but I did. I was ridding it and got it warmed up to N.O.T. and I noticed that it wasn't getting on it right off idle, but once the RPM's got up a little the front end popped up and it shot out like a f-ing rocket. I took it back into my shop and put a fan on it and simulated what I did. If you take it from idle to WOT fast it hesitates for like a second maybe two then starts to pick up and when I let off it backfires. I do live about 3500 feet elevation that might be causing it. Is backfiring caused from too rich a mixture or too lean? What would you suggest that I do?

[1iviper]

check your jetting,especially maybe going up a size or too on your leak jet.if your jetting is good it's prob the leak jet being to small.a couple of companies are selling larger(holds more volume)accelerator pump covers but the leak jets are cheap and do just as good a job.

[Colby@C&DRacing]

The new boysen quick shot will fix the problem you are having. When you rapidly open the thottle you are leaning the air fuel mixture out and the accelerator pump is not giving your bike enough fuel to compensate. The quick shot is really easy to install and works wonders

[sampleez]

the leak jet seems to be just as good as the boydseen part. just order a $5-6 jet (a #35, stock is a 50 or 55 i believe) and ur good to go.

the leak jet is backwards in sizing than other jets. i got a #60, and it made the hesitation worse. so now i gotta go back to the dealer and switch it out for a 35

[PurePerformance]

Get a 35 leak jet. This takes care of all the hesitation problems.;)

[raptorrider]

is the "leak" jet the same as the pilot jet or what?

we are having the same problems here.

[sampleez]

not the same as the pilot

it's not on the yfz microfiche to my knowledge. i think my dealer found it in the wr450 dirtbike microfiche.

if i remember to, i'll try and get the part # for it