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Need help getting bike running PLEASE

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So here's the deal. My good friend who knows bikes and engines very well owned this 2004 YZ450F, he was riding it one day-and this bike ran great I mean like new, everything on it ran so smooth-anyways he was riding and was just coasting down a gravel road at like 10 miles per hour and the bike just stopped. If I recall correctly he was in neutral even. The bike never started since so he let it sit for about a year and just gave it to me and he bought a brand new KTM so didn't really pay attention to the YZ. I guess he tried to get it going but didnt put a lot of effort into it since he has his new KTM but he said he thinks it is the CDI box because it just ran too damn good to be anything else. So I bought a CDI box and dropped the bike off at a local Yamaha dealership and they are going to try and get it running. They are going to flush the fuel system and rebuild the carburator and I gave them the new CDI to install if needed. The kickstart kicks just fine and has plenty of compression and there is definatly no noises coming from inside the motor like the timing chain or something. He always trail rode this bike was the only owner and never raced it and it was well taken care of. What could be the problem? Here I am sitting just hoping and crossing my fingers that the shop can get it running with the parts they already ordered and are still waiting for along with the CDI if that is what it is...it has been a long time since I had a dirt bike, used to race when I was younger but that was 2 stroke 250. Does this sound like a carburator related or electrical related or some kind of an easy-ish fix? Your input is greatly appreciated.

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...again the kick starter moves just as it should. I should have waited until the cdi box came in before dropping the bike of but they are going to flush everything replace all filters install new back tire clean/rebuild carb..man its all I can think about..

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Probably needed a valve clearance adjustment 10 years ago....

Seriously, until you start going through the bike and checking all the systems for good health, there is no way to know what is wrong.

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Crap..even though it was never ran hard like at all. And there isn't a horrible amount of hours on it. It was running like a top and then suddenly stopped like it ran out of gas but didn't run out of gas.

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37 minutes ago, YZF1825 said:

Crap..even though it was never ran hard like at all. And there isn't a horrible amount of hours on it. It was running like a top and then suddenly stopped like it ran out of gas but didn't run out of gas.

I would inspect all the major systems, and you might find something simple like a loose plug cap or a worn wire insulator...

Plug/plugcap/plugwire/coil/coil ground/stator/stator harness/kill button

I doubt it is carb related, as they don't just 'fail' without some warning. 

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So check it out. The head mechanic had a 05 RMZ 450 barely ever riden and I know this because I know the guy. Just to do it he installed Weisco piston and rings and crank, standard compression 12.1:1. Has after market wheels, FMF Power Core 4. Boeyson Carburator kit or bowl or something it has the Boyeson emblem on the bowl. Racetech forks, after market handle bars chain and sprocket and is 100% condition looks brand new and is faster than HELL. Was clearing some good sized table tops no problem today. So the deal was trade my yz450f which was really jacked up in the head and the valve hit the piston when it jumped 8 teeth and a grand. He hooked me up as a favor hes a good friend of mine. Also has ASV Levers the unbreakable kind..today I actually bent one outward and am hoping to find just the lever. Its bad as hell and I am getting used to some of the tight trail riding we have.

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