Bike down, i repeat bike down

[racerfty]

I need some thoughts on a no start on a yz450f (05)
Bike was loosing power and burning oil, went for the top end job, upon tear down i noticed the root cause of all the problems were the top two rings aligned the gaps and burnt a nice hole in the cylinder. Ordered all the parts new cylinder (oem), wiesco piston, gaskets (oem), got a valve job done at a local shop (kaw) (i know the dude and he does grade A work). Also new timing chain, hot cams stage one, and a rev box. Assembled the bike shimed the valves, attemped to start it and just a whole lot of kicking. Checked the cam timing, good, checked the shims, perfect, checked the spark, ok, checked fuel, good. assembled again and kicked some more. still nothing. Replaced fuel drained carb, kicked and kicked some more nothing, checked on line, did everything from retarding the cams one tooth to adavacing making sure no piston to valve contact happened kicked and kicked, nothing. one note tho, with exhaust cam forward one tooth compression high, due to auto de comp, and will back fire once in a great while. exhaust cam back one tooth normal compression and rare backfire. got sick of kicking dragged the bike still no life, switched out the cdi to stock along with stock cams nothing. i am out of thoughts, plans, and energy, and clues or hints to a last ditch effort before i spend an arm and a leg at the yamaha dealer?

Also does any one know if the spark plug fires on both comp and exhaust tdc's ? and if not how does it know what stroke it is on, just to make sure i was not on the wrong stroke i attemped to swap timing of the cams to the opposite stroke, and nothing changed.

Thanks in advance for reading this and thinking about it.

[KKXR400R]

Rag in the airbox?.........

J/K

Sounds a little strange to me. I would pull the carb and make sure the accelerator pump is squirting. Other then that I you have all the components (fuel,fire,air) so I can't imagine what could be going on.

-Kevin-

[racerfty]

Kind of funny you say that, around the 2nd day of wondering what the heck, i was holding the carb in my hands and just staring at the engine side of it when my buddy not knowing cranked the throttle and with my luck the accelerator pump shot a jet of fuel in to my eye, then i opened my mouth to say stop and the rest of the shot went in to my mouth. lesson learned 1, fuel in eye hurts, and makes things blurry until it is washed out and 2, gas is not the best tasting item on earth. i guess the yz is getting even with all the hard core riding and jumping i put her through, or maybe i should start using warm water in the pressure washer.

[cowboyona426]

Going out on a limb here- have you eliminated the kill switch as a possible problem? Have you trouble shot the electrical system and checked all the connections?

[racerfty]

i have not checked in to the electrical system as of yet, but if there was a problem ie kill switch there would be no spark, at least that makes sence. i pulled plug, lots of spark, good compression, cleaned the carb, found nothing inside as in dirt, and everything is good and where it needs to be. i am going to try to put the old cams back in and see if that helps at all. so i got spark, fuel, compression, it is in time and valve clearance on the money. ??????

[ktm_cody_199]

Nothing ganna be wrong with the kill switch because he has spark,these four strokes sure do have temper tantrums dont they, also going out on a limb here.....Did you put a high compression piston on it??Some times an old coil and a HC piston wont work together You sure did confuse me

[pjg351]

Have you checked the timing at the fly wheel, and made sure the stator plate hasn't moved, or tested the coils in there, i've had troubles with them before, you need a multimeter.

[racerfty]

no i checked the piston, it is stock 12.5:1 i think is the compression i know it is not the high compression, i was even thinking that maybe by chance i had a wr piston in it, but i checked and the part numbers are the same. i put the stock cams back in, so now with exception of piston every thing in the engine is yamaha and has been there before the teardown. but putting the stock cams in i dropped one of the clips on the cam in to the motor, did not have a magnet small enough to go in, made an electo magnet out of a screwdriver and wire, but did not have any batteries, so lond story short, i have to remove the flywheel again to get the clip and i did have a rag over the hole, it went into the space for the cam chain. i did not check the stator, will give that a shot, i am just thinking that with spark, that kind should give me something like a pop or sputter, i did tear the head back off to make sure i did not bend a valve. Took it to the local yamaha dealer and they said it was tight and not the problem installed it with new head gasket and still nothing. what kinda has me on the wall is i am a mechanic who works on Cat machines, i am a dealership field tech who has repaired millions of dollars worth of machines, and i cant figure out what is wrong with a simple dirtbike! taking it to a yamaha dealer is like admitting failure, but after tomarrow i think i will admit defeat and take it, at this point i am tired of turning wrentches for free and would like to ride. if that power was not so addicting i think i would go back to the tiddlers.

[pjg351]

Let us know the outcome, good luck

[racerfty]

well here it is, the bike is running, dont have a clue as to what i did, i did check the stator and it was fine, installed the plug, gave it a pep talk about how this was the last day i mess with it and was going back to the 125, kicked nothing, had the exhaust off, kicked again with my hands neat the exhaust port, and it backfrired, it was hot. did it again with out the hand and it sputtered. installed the exhaust, air box, timing plugs, kicked a few times and it lit off, ran then stalled, adjusted the idle and it lit right off, broke it in and parked it, need to change oil, filter, adj the valves and finish assembling it. So if i had to say what helped, had to be the pep talk. thanks to all who helped. and if any one needs to know anything about a 03-05 yz450f ask me, i have had that bike apart so many times, i can assemble it in the mud at night.

[ktm_cody_199]

My bikes got the pep talk many times,but it wasnt always a nice one glad your bikes running,now go punish it

[Florida 393]

If I could find my old thread from 2003 on my 426F not starting I'd link it here. Mine turned out to be a pin hole air leak in the o-ring between the intake bell and the carburetor body. A simple $1.50 part I now keep 2 extra of on my spares box. Glad you got it running. This sounds like some tiny grit in a pilot jet or one of the slow speed passages.

Bill

[dklassen]

"and i cant figure out what is wrong with a simple dirtbike!"
A simple dirtbike is a YZ250 two -stroke!

[Flash393]

That's great you got it running finally!! I was wondering though if you are going to put the new cam back in and see if she still runs?

[ktm_cody_199]

I would