i had my 426 out for the first time today. when the bike was hot and running i would hear at low speed a slapping noise possibly from the top end area. also the bike would just stall every once in a while. i have never had the top end apart. i just changed the oil and filter and the spark plug. the outside temp was approx. 56deg. farenhiet. could this possibly be piston slap or a timing chain streched ?? thanks for any help. oh yeah the bike rips and i smoked all the 2-smokes out there today.