won't start loud backfire

Started fine a few weeks ago,took front wheel off and bought new tire and re-installed then it got cold and didn't start for a couple weeks. started hard , like on three cylinders put in an old plug i had and it started better. every time I started it in the last week it started harder and harder. Now it cranks and cranks ,if I crank it long enough it will back fire really loud and now it won't start.It's getting fuel, fair spark, maybe a timing issue?

 

Check float levels how long have you had the bike?

 

You said swapping a plug helped, have you tried just putting *new* plugs in all 4? Sounds like it couldn't hurt if an old plug helped, cheap thing to try, fast, and you need it anyways, AND it will get that issue out of the way for further diagnosis.

 

Sounds like fouled plugs... replace the four with new ones and see what happens

 

very strange...it started today but was sputting and popping, I rode around the block and it started running better, I made it to the gas station and filled up with premium and it's running like nothing was ever wrong. Maybe had some water or something in the tank from sitting all winter(I did have stable in the gas) I guess we will see If it starts and runs normal tomorrow when it's cold.

Thanks

 

Had the same problem but I took off my back tire, started day before, went to start it day i put the new tire on and it started back firing over and over. Wouldn't start for anything even with Starting Fluid... Yesterday it started, then took off the choke and soon after it died like the engine was flooding so im thinking it is one of my carbs like a float is stuck.. You yourself may want to put some Cleaner in your tank or even give your carbs a good cleaning.