Hey guys, So after replacing my cylinder head, everything is running great except for one problem - the valves seem to require constant re-adjustment. It was my mechanic that did the cylinder head rebuild, I did everything else myself. About 1000km of riding after getting the bike running, it was having real trouble starting from cold. Using the choke would have no effect. Once I turned the bike over enough and the exhaust warmed up I could get it running and once it was hot it would run just fine. I brought the bike back to my mechanic and he re-shimmed the valves - this made the bike 100% perfect again. Unfortunately this only lasted another couple gas tanks of riding before the starting issue happened again. In addition to the cold-start issue, it would also seem to backfire/pop a helluva lot more on my hard decels. I ride the bike fairly hard, and sometimes have my girl on the back. I'm wondering if riding too hard is causing this problem to recur so quickly? On the same hand, the bike should easily be able to handle what I'm using it for and I can't understand why the hell the valves would need re-adjustment again so quickly. Do you guys have any advice on what could be going on? I need to know whether to call the mechanic out on his work and ask him to warranty the poor work he has done, or whether the cylinder head I used may just be &%$#@!ed up and require machining or something (which would realllly not be cool). Here's a quick breakdown of my setup for reference/clarity: 2005 DR-Z 400sm w/newly replaced used '07 400E cylinder head. everything engine-wise is stock. 3x3 airbox mod, rejetted carb, ssw/mrd exhaust. Cheers!