backfire

Hello folks

my 03 450 keeps b/firing everytime i back off. my old 400 did the same but not every time any ideas , i will be looking at the valve clearances and fueling , :applause: need some ideas where to start first the bike is bog standard and is uk model

It it just small backfires or more like a 38 being fired? Small pops are normal on declaration. A backfire is either usually caused by an exhaust leak (cold pocket of air in the exhaust) or lean jetting. What jets are you running??

Try a half turn out on the fuel screw. If its popping and bogging its lean.

thanks for post >> big flame from rear some times im told and dont know about jets will look at plug etc ref mixture yet

Usually, backfiring or popping on deceleration is caused by lean jetting or an intake manifold leak.

thanks for post >> big flame from rear some times im told and dont know about jets will look at plug etc ref mixture yet

Byggd right!

Big flame backfire (blue) would be from header or exhaust. Maybe leaky carb boot, but flames I would say exhaust.

I would check everything, but your exhaust first. Just your header out of allignment can make your bike spit foot long blue flames (trust me, been there....) If you have an air leak, jetting changes won't do much all.

You might want to change your exhaust gaskets, when is the last time you changed them?

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