Backfireing

i guess the following should be checked-
Fuelling, Air filtration, Timing ( cam or ignition) and/ or valve clearances.
in no particular order.. andhas any work been carried out recently?
but if it was my bike i would run a quick compression test to close out any inlet valve leakage as this might be a sign of a bad valve to seat seal on the inlet side

 

first i would do is check the cam timing marks line up, as if it wasn't doing this before, then the inlet valve is opening/ closing slightly off the designed parameters.
i have something similar before and it was a result of a burnt inlet valve/ valve seat and the combustion process was being allowed to push back into the inlet manifold.

if you can, pull the spark plugs, and hand rotate the engine in the normal rotating direction, using the back wheel in gear if necessary.
and when you get the lower timing point aligned to the timing mark then check the position of the camshaft

 

Check the fuelling and TPS, sounds like it's running lean.

 

in any circumstance of route cause analysis, my first question is 'what has changed', and as you have just renewed the belts that would be my first port of call..

 

could be many things as already suggested, does it backfire more from cold/warming up or worse when hot or all the time? Is it running ok apart from that - e.g. on a constant low or high throttle opening?

 

Checking you’re not one tooth out on a belt has to be a good idea.
However, I am amazed at the result of a TPS reset on my 999.
I had always associated a TPS reset with a bike that wasn’t idling properly and was prone to stalling.
However, I was getting a misfire on fierce acceleration at high revs and was strongly advised to do a tps reset by both Derek and Chrisw.
I duly downloaded Scan 5MX to my Android phone and ordered the lead and OBD reader to go with it, as recommended.
Pairing the he reader to the phone was easy but getting the app to talk to the reader was less easy, perhaps because the ECU times out after 10 seconds if you don’t start the motor.
I think it may be worth starting the motor for the initial ‘handshake’.
Once the app and reader were talking it was super simple to reset the TPS and also the service symbol.
When I started up afterwards, the improvement was immediately obvious.
It started even better and the idle was very much smoother.
When I came to ride it, the motor was much smoother and also pokier. Plus, the misfire was gone - result!!

 

Indeed, which was why I suggested it above.

My 916 started running really rough some years back, wouldn't idle properly, would stall if revved at standstill and was popping and farting under acceleration from lower RPMs - turns out one of the 2 screws holding the TPS in place had broken and the TPS had moved, wasn't massively out (in terms of MV setting on closed throttle) but enough to run like a bag o' shite...

 

any backfiring on a BIG trailing overrun?