I put an fmf titanium powercore slip on on my bike last summer. The dealer who i bought the muffler from said that i would not have to change the jetting with only a slip on. So i took ths pipe home put it on and ran it and it ran good for like ten minutes and then i put it away for the nite and came back out tomorow and it started and i let it idle for like 5 minutes. I came out 10 minutes later to go riding and it wouldnt start. I thought it was flooded so i took the carbeurator out and properly installed the correct size jet. It still wouldnt start so i took it to a machine shop in town where i was told that all my clearances were good and that the cylinder and the piston were fine. I took it to the dealer a few weeks after and they told me i needed a new top end which i think is load of shit because the guy at the machine shop (who's been building motors for years) said that it would just be a waste of money to put a new top end in and that everything was correct. I recently put the motor back together and double checked everything before putting it back together, timing and all. It still wont fire even when i put fuel in the cylinder. It is getting spark but it just wont fire. I heard from someone i know that it might be the fuel/air mixture screw, could this be the problem. If you have any advice, please let me know, i would greatly appreciate it.