CRF 450R only starts when pulled please help me!!

[BlasterMaster15]

dont mean to put this on theblasterforum but everybody on here is so helpful and nice compared to other forums. so i have a crf 450r motor in a 400ex modified frame for a hybrid quad and i bought it non running. pretty much it has hotcams,full hinson clutch, je piston, and a tc racing straightpipe kinda exhaust. i had to replace the crank in it and i also did all the gaskets and seals in the motor. everything is in time the only problem i know it has is that the valves are loose becuase i guessed on the valve shim sizes.they are about double as loose as they should be. i think it has a 45 pilot jet and maybe a 178 main in the carb. i cant for the life of me get it to start from the kicker cold only starts cold by pulling it with a truck but it runs great when its hot and sometimes fires up from the kicker when hot. i took it riding last weekend and i thought i blew the motor because i was 4th gear wide open and it randomly died and refused to restart, i still dont know why but when i took the motor apart again everything looked fine. i cleaned everyhing up inside and honed the cylinder too. i didnt replace the rings on the piston though. if someone can help it will be greatly appreciated.

 

[Awk08]

i'd be checking compression against what is called for, rebuilding the carb and definately getting them valves adjusted properly.

 

[Kgibson]

it sometime starts when hot because it closes the lash. Exhaust should be .010 - .012 and intakes at .004 and .006 . Until u get the valves right there is no point in trying anything else

 

[Braaaptor]

it sometime starts when hot because it closes the lash. Exhaust should be .010 - .012 and intakes at .004 and .006 . Until u get the valves right there is no point in trying anything else

There you have it! Valve lash problems will make the engine difficult (if not impossible) to start cold. Plus loose, rattling valves rob you of horsepower, hurt throttle response, make the engine feel lethargic, and hurt fuel economy. Oh, and if the valves are TOO loose, the shims can pop out and the engine will eat them for dinner. Not good.

You can get a cheap feeler gauge for a couple bucks at the local auto parts store. No need to guess on shim thickness. It just takes simple math and a feeler gauge to set the valves correctly. Do it now, and keep a check on it every 15-20 hours thereafter.