My bike has started missing, backfiring; when I'm coming out of curve and want to roll on throttle, it feels like it will die. Even in 5th gear at high speed, it will miss. I had same problem last year and took to BMW dealer. I've taken to dealer again and asked them to check the plug, etc. I'm wondering if it's fuel??

this sounds like a timing problem

Get the fueling set up on a rolling road. Bike makers set the fueling up to match the exhaust they fit. Your new exhaust will have less backpressure and this will cause popping when you close the throttle to slow down. It will also cause hesitation when you accelerate.

KICK HARDER TRY PULL STARTING IT..IN SECOND GEAR..DOES IT HAVE ENOUGH COMPRESSION TO START?IT SHOULD START PULLING IT...START OFF WITH NO THROTTLE THAN IF NOT STARTING CRACK THE THROTTLE SO LIGHTLY AND SHE SHOULD FIRE OFF WHILE IN GEAR BEING PULLED OF COURSE BE CARE FUL NOT TO RUN INTO. WHO EVERS PULLING YOU..USE A LONG TOW ROPE..IF YOUR NOT A SEASONDED RIDER AND KNOW YOUR BIKE VERY WELL I WOULD NOT ATTEMPT THE PULL START...IF NOT CHECK YOUR COMPRESSION AND TIMING..MAJOR VACUUM LEAK MAYBE AT BASE GASKET..IS ENGINE SUCKING TO MUCH AIR? GOOD LUCK..

Klacking noise? Any sort of mechanical metal to metal noise is no good. If the engine pulls fine once your in higher gears with no noise I would think that it is transmission/gear issues and not engine(piston/rod) issues. If the bike gets abused or stunted chances are the first couple of gears are bad.

More likely to be your ignition coils. They heat up and expand this can cause an open circuit which will close up again when it has cooled down. Although, a bad charging system may cause this problem. Check the battery voltage with engine switched off ( approx 12 volts) and with the engine running (approx 14 volts) If you are getting 14 volts then your battery is dead, if you aren't, then your charging system has a fault.

Sounds like the carb is frozen or the ignition timing is way out (check distributor and loosen the clamp, turn it slightly with the engine running until it idles and revs up nice) . Reset the ignition timing, if that does not cure it, a carb rebuild is on the cards.

Vote for me if this helps, thanks.

I would say it is a faulty engine temp or Air temp sensor,

Run some Seafoam through the carbs. Should be available locally at a parts store. Mix with your gas according to directions. This will clean out the carbs, which sound like they are a little gummed up.

Sounds like the clutch might be going bad.

Clutch slippage would be a possibility. While rolling in 5th gear mid-range in the rpm band give the bike a lot of throttle. Do the rpms rise significantly without the speed of the bike increasing? If so you may need a new clutch or possibly just new springs. If you have put any oil additive it is possible your clutch friction plate(s) became contaminated.