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New rebuild won't idle right, hard to start.

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I bought a 2008 yz250f and rebuilt it first thing due to bad valve clearences. I had the valve seats recut and went to stainless valves and matching springs, a brand new cylinder, wiseco piston and gaskets, it supposedly has hotcams, but that is only going from the previous owners word.

 

I got it put back together and fired up but it was difficult. It seems to get very hot very quick. It idles kind of high and dies after maybe 30sec of idling. After that it is very difficult to start, and usually requires me to "pump" the accelerator pump a couple times and the throttle to be 1/2 to full open to start. Also, I am getting popping/backfiring with any acceleration or deceleration of engine speed (in neutral since I don't have anywhere to ride it at home). I know a little bit of popping on deceleration while riding and in gear is normal but this doesn't seem the same and I'm setting still in neutral and only coming down from about 1/3-1/2 throttle.

 

I havent had a chance to ride it since I bought it, now I got it back together and I'm afraid to ride it out of fear I might screw it up after dumping a ton of money in it. Any help would be greatly appriciated!

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Alright, well I'm getting ready to pull the pilot, check the cam timing, and check the valve clearence. How can I make sure the Hot start is working properly? I'm not even entirely sur how it works. I know it opens passages in th carb, but that is the extent of my knowledge on hot start.

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Simple. Remove the plunger, inspect it (rubber seat on the bottom of the plunger). Check the bore where the plunger rides for cleanliness. . Reinstall, confirm there is freeplay in the cable and when you pull the lever, it moves smoothly and appears to move the full distance.

 

 

All a hot start does is open up a passage way to allow extra air in as a hot engine needs less air to run (leaner) at idle. Usually, it is used because a rider fell, and when fallen over, the bike floods out and stall, causing excessive fuel in the carb and cylinder.

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