On the Mikuni site you mentioned there is all kinds of trouble shooting tips for guys like me to read through, great heads up for that site.

went to the general tuning giude and it was full of info on backfiring etc.

... gives me a few things to look over already this weekend (Y)

 

Glad you found what you needed. I find it much easier to read and absorb as much as I can...then I can gain a better understanding of what needs to be done. If you rejet, make sure you write it all down in a safe place! I live at 4200ft, so when I go to the coast dunes, I have to rejet. Sans the EFI sportsmans! I only have to rejet the predator. Still like tinkering, but done with the 2 strokes!

 

<div class="FTQUOTE"><begin quote>Originally posted by: BigBros_Farmtoys

From my wrenching days, a Backfire is caused by a lean condition.. That usually points to an exhaust leak as the primary cause.

Even if you don't hear the leak it could be seeping enough cool air when you let off (pressure change too) to lean out the pipe and thus cause a backfire.</end quote></div>

^ is correct BUT another thing that can cause it is a small foreign piece of debris in your jet. SOMETIMES not all but SOME, you can drain your carbs float bowl and the dirt will flow out of the jet&bowl and correct the problem. Its good that you pay mind to little things like that because they can and have led to bigger problems if not corrected. Let us know how you make out with it please.