Ok so im pissed like bad right now.... My 2007 yz450f is telling me that its going to be a early grenade. i do alot of preventive maintainance like clean air filter after every ride. change oil every 8 hours of trail riding or every 2 visits at the mx track or every race. i re-lubed everything on the entire bike. ive re-shimmed the valves once i check them regularly i run 94 obtain from chevron in it. i clean it after every ride. ok to the point!!! i removed my seat. took a look at the breather tube... every time i clean air filter.. what the **** full off dirt and sand and sticky shit. put a piece of paper towel down the hole pull it out, full of sand and what not. so that tells me their is crap in my engine. alot of it at that! cleaned out my airbox with a rag damped with gas. not drenched just dampened to get the dirt off the plastics. removed the air filter. was still pretty clean but it was dirty on one side. i always clean it anyway. (no-toil air filter) i use uni air filter oil because no-toil is the worst crap ever made. look down my air boot. dont see much. run my finger down it. DIRT GRIT CRAP all over. Hm so now i know my internal engine components have been fully exposed to the worst of the worst. SAND! i cleaned it all up. and put a very very light layer of lithium greese on parts of the air boot to catch what comes though the air filter. i used lithium greese for a sealer around the air filter. (alot of it).. i also drench the air filter in oil and ring it out slightly because its not the air filter that filters, its the oil so i use extra oil. i now installed a twin air filter, that my dealer soaked in bellray filter oil. i thought id try it before i buy it. so im waiting on how that works. if this does not work. im selling this 4suck and buying a nice new KTM250xc and never have stupid valve breather tube problems or a engine that sucks more air then a bigblock chev!!! 2 stroke barly sucks air compared to the 450. UGGGH so angry right now. i thought japs were smart?