When you say backfiring do you mean popping back through the air cleaner or popping crackling out the exhaust?
The pipe at the back of the air box that you blocked is the air injection, witchI believe feeds fresh air into the exhaust ports thru a pair of reed valves in the head and is controlled by the large valve just behind the airbox.
The crankcase breather goes to the front right corner of the airbox.
If too much air is being bled into the exhaust it will mess with the O2 sensors cursing a over rich situation.
Also check for leaks in the exhaust system.
Hi mate,
The popping and crackling is coming out of the exhaust not through the air cleaner and is joined by the smell of fuel.
I am working on the valve clearances at the moment but when I am done (if the issue remains) I will start looking at the air injection, reed valves and inspect the entire exhaust system again.
Makes sense to me
Since fitting Staintune mufflers I get a little crackle from exhaust but a lot of bikes and cars with aftermarket exhausts does it
But not actual backfire
But I don't get a fuel smell
Sometimes sounds good
I put the aftermarket exhaust cans on the bike shortly after getting it and have always had a bit of a burble but this is nothing like that, it will backfire (pop) even when changing gears while riding
But when it is working properly it really sounds good