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06 YZ250f wont crank cold!!

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Hey everyone, i have a 2006 yamaha yz250f that i recently bought from a friend. It has been bored out to a 266 and has hotcams, drd exhuast system and some other stuff. Well when i first bought it, it was pretty easy to crank cold and hot but gradually it has been getting harder to start. Now, it WILL NOT crank cold by kicking it with choke on or off and hot start. I have to push start it to get it cranked but once its hot or even warm it will crank on the first kick almost every time, no matter how long iv been riding it. I service it routinely and i just put a fresh spark plug in it. It feels like it has good compression and the spark is good. It was just bored out and valves checked and everything by a trusted mechanic not too long ago when the previous owner had it. I have also messed around with the fuel air mixture screw hoping that was it but no success. It runs great when finally cranked but it is just a pain in the butt to get started. Any help would be greatly appreciated thanks!!:smirk:

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I cant remember if valves too tight was hard to start hot or hard to start cold. Might want to check the valve clearance again

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Yup, cold hard start is often valves. Hot hard start is often too rich on the pilot.

If it is valves, they can go in a single ride from being in adjustment to fully closed up.

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Well i was hoping it wasnt the valves but then again, im not a very lucky person. Thanks anyways guys. Ill take it apart and check them when i get a chance and ill let yal know if it works. I greatly appreciate the help!!

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Quick question, do yal think it would have anything to do with the weather here. i live in eastern north carolina and when i bought the bike and it would crank fine, the temperature was around 50F. But it seems like as it got hotter, it got harder to start cold. The temperature here now is like the hottest in a long time at around 95F.

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You will definitely have to at least play with your idle mixture screw maybe go down a size with the pilot and up a clip position. Do the idle mixture screw and go from there but check those valves first!!

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okay i checked the valves and come to find out, one of my three intake valves was really tight. so i changes the shim and got it back in spec and measured the others and they were fine. i put everything back together and did the proper cold startup procedure and it still would not crank with the choke on. it sounds like it wants to though. i turned the choke off and pulled the hot start in and gave it a hair of gas and it fired right up. so i guess im back to the way it was but at least i can kick start it now. any ideas on why it wont crank with the choke on?

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Just a quick question, not try to steal the thread, but im have the same problem. when i go to check my valves which i will be doing shortly, does tdc have to be on intake or exhaust or does it matter? thanks!

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TDC of the compression stroke. You will see the timing marks on the flywheel. If you line up the "I" not the "I--I" correctly on the compression stroke the lobes on the cams will be at the 10 o'clock and 2 o'clock positions

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