[NickJohnson990]

I have a 1997 xr100r and i got fmf for it and it has a crackling noice when I'm going fast and then when I let off the throttle it backfires, are the jets too small?

 

[retro]

The exhaust is probably leaking either at the head or the muffler joint or from a hole or a crack in the exhaust somewhere. You'll need to fix any leaks completely before you attempt to rejet it.

 

[NickJohnson990]

Does a whistle have anything to do with it it only does it at a curtain low rpm.

 

[retro]

Dunno... can't hear it.

 

[NickJohnson990]

I can hear the whistle and its actually pretty loud when I'm at a curtain rpm