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2010 YZ 250F extremely hard to start

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I just picked up a 2010 yz 250f with a 269cc big bore cylinder and hot cams, both intake and exhaust. It is ridiculously hard to start, like to the point were I cannot kick start it at all. I checked the valves and intakes measured at .005, and exhausts measured at .008. I know this is barely within spec, but regardless it should still not make the bike THAT hard to start. Also tried a new plug and tested spark, no luck. Bike was jetted by pro circuit and is extremely crisp (when you actually manage to get it started..). Anybody have any helpful suggestions?? Thanks :thumbsup:

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I know what your saying, yeah it does have alot of compression but that is expected hence the bigger bore, etc. And it is hard to start like i can kick it a ton of times and it shows no sign of even wanting to start. I did eventually get it to kick start by kicking it quickly with the throttle slightly open about 15 times. The funny thing is it will start 1-2 kicks when it's warmed up, but when it's cold it's near impossible to kick start...and again the valves are in spec so that isn't the problem.... i'm confused. :thumbsup:

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Do you know the proper starting procedure for a 4 stroke? You don't start it at all like a 2 stroke. Don't want to sound like I'm calling you dumb, I just don't know your history of bikes. If you are starting it correctly then look at your jetting and make sure it's set up for your altitude and temp, also make sure the pilot jet is not clogged.

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Oh yeah, I've owned quite a few 4 strokes and know how to start them, so that's not the problem. The jetting is spot on, this bike has to be one of the best jetted 4 strokes I've ever ridden. There is no bog what so ever. I will have to check the pilot jet, but I doubt that's it though considering how well it runs when started. And I don't know the piston compression, I'm guessing its 13.5:1.

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Next time you go to start it from cold, try this....choke on, 3 quick twists on the throttle then kick - right hand off the bars.

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I think it's hard to start cold is valve clearance. Hard to start hot it's too rich but he said the valves are within spec so that's not it.

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Honestly, I think it just might be that I needed to find the trick to starting it. I went out to my shed today to mess with it again. All I did was give it 3 twists of throttle, pull the choke, kicked it to TDC, kicked it over once and fired right up! Hopefully it stays this way! I know modded bikes are very tempermental and starting procedures sometimes vary from day to day depending on the temp, etc. I had a modded CRF250 a few years ago and that thing never wanted to start... then again it was a Honda :thumbsup:

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What jetting are you running? I know you said it's correct but humor me, I'm just curious. I'm running pretty much the same set-up as you but mine is ported. I had mine on the dyno before after the engine work and the MJ needed changed big time.

Here's what I'm running:

MJ #160(178 was stock)

PJ #42

LJ #50

'09 needle in 4th slot

temp. 80 F

elev. aprox. 800'

You're going to love the set-up once you get the starting dilemma straightened out. Good luck. :thumbsup:

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