just bought a crf450r, my first and i love it. after owning it for 5 minutes tho i realised that it didnt start as it should from warm or hot and googled the problem. i was overwhelmed with inlet valve issues so i checked my valve clearances and sure enough one valve had no clearance wotsoever! i pulled the head off and removed the now chewing gum like titanium valves and replaced with ss ones. i did not lap them in as my local dealer said the seats would not like this? after fitting the ss valves i poured petrol in behind them and there was no leak at all past the valves. ok. stay with me lol . i put the thing back together and? starts fine from cold, then after a period of 5 to 15 mins it holds back, hunts, splutters, back fires on a cruising throttle load, wont start if stalled. please, stay with me because of the symptoms i suspected fuel starvation so i fitted a in line fuel filter 2 c wot was happenning wiv the fuel. i put it between the on/off fuel cock and the carb. after riding the bike for 10 or 15 mins i could look down and the filter would be empty of petrol and the bike would play up! i have ran the bike with the petrol cap off so 2 check for a vacuum and it behaves the same. i have let flow a tank of petrol into a container and it runs free from the tank could the inlet valves affect the fuel flow? please help me as im gona chuck it on its side and leave it there soon!!!!!!!!!!!!!