Well! the backfire/afterfires are genetic trait for the s40. Mine POWED often. At first I got surprised every time but then got the hang of it. In stock condition the muffler sound was anemic so I did the hartmann mod(we don't have HD m/c's here). The backfire/afterfire became LOUD and at times bothersome. I did not want to do the spacer mod so it took a drill and gently made a hole in the air mixture screw brass cap in creasing drill bit size progressively till I was able to insert a small screw driver in. This way the brass cap remained there as a safe guard for the mixture needle ever falling out. I rode the bike to its operating temperature stopped and turned the mixture screw CW (took1/2 a turn). Then I turned it CCW about 1-1/2 turn.
MY PROBLEMS WERE OVER
. 98% of the afterfires are gone. This is good enough.
I live in Pakistan, islamabad elevation approx 1300feet. Summers are hot 42-45C. we have mountain resort nearby (50km) elevation 7500+ feet, now during the climb the bike warms ups and if we decend fast I get a big BANG..... OR after hard riding (80mph) then a BANG. But this is now very much acceptable
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