[motosicko]

Just had my 08 450R ported,and new top end, and got it out Sat. for a quick break-in.
It runs good and strong, but was getting a little back-fire on decel. So I put a richer (178 from 175) main jet in and it helped a little. Question is: Does a port/polish generally require richer jetting? The guy that ported it told me he though the jetting should remain the same. I'm going to check the plug tonight for a true indication, just thought someone with port experience could shed a little knowledge. AS?? or any one else??

My thoughts are that if you increase the flow without adding a little more fuel, that it will be drawing more air, in turn leaning the mixture.

[Asmith]

You are correct if the porting is done well and you haven't sacrificed velocity for volume.

The decel pop is a pilot jet issue as the main is closed on decel.

What pilot are you running?? 45?

[motosicko]

Yep 45. Needle clip 2nd down. Temp was a bit cool at 45, so I richened up the fuel screw a bit. it didn't pop very much after the main jet change, only on the stand while I blipped the throttle, and maybe once on the track, minor, but it's been so perfect in the past.
Thanks for verifying that I should need the adjustment.

[woodsman]

I went 1/8 - 1/4 turn in on the fuel screw and that seemed to fix my backfiring issues.