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YZ hard to start ONLY when cold.

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Hey guys so I picked up my first 2 stroke a month or so ago after being on a 250f for a year. Anyways the bike is a pain in the butt to start ONLY for the first time of the day. Even if you let it cool down all the way it will still start first kick, but not if you let it sit overnight. So far the thing rips when riding it and is no slouch, again it fires up first kick every time except for the first time of the day. Could there be any jetting problems? I've only fouled one plug (yesterday) after about 6 rides I believe. I'm fully capable or working on the bike but have never had the best of luck when tooling with the carb. Any help would be great!

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Just curious on what year your YZ is??? I have hard starting bikes before and found that the choke was not going full open. I would also check the float level height as well.

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That happens to me too unfortunately if I don't start the bike for 2 days. So I start both ever day now. I think it the reed with the oil of 20:1 the maybe do not open? 

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Check the compression. My old yz was hard to start the first time and easy for the rest of the day. It had 130 psi

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Thanks guys its an 05 yz125 and the intake boot has a small tear (behind the clamp so it shouldn't affect anything) but I'll have to fix that and I'll check the reeds as well. What is a good benchmark for low compression? I've never measured it before

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150 psi usually is a good time to replace the piston and rings.

Or if you know how many hours is on the piston you can go by that

Cast piston -30 hours

Forged -50 hours

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In my case it happens on both bikes that is the funny part actually, one with a stock YZ250 ignition, spark being fine, the other a vortex ignition spark also being fine.

Reeds are new (6 hours) on the other they have way over 80 hours but in both cases they seal just fine. Boyesen Power reeds for both bikes.

 

I ride mixed off road, some quite open with ample possibility to ride 4rth Wot, and trails where second half throttle is the most one can do without getting into trouble. 

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150 psi usually is a good time to replace the piston and rings.

Or if you know how many hours is on the piston you can go by that

Cast piston -30 hours

Forged -50 hours

The previous owner put a top end in 2 rides before selling it, so I'm planning on replacing it at around 40. Actually yesterday afternoon a parent's friend who has grown up on bikes and racing bikes got on it and said it runs like a brand new bike. That makes me think the compression is fine.

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If all else fails, try going old school.  Lay the bike over on the side for a couple seconds (until gas starts dribbling out the overflows).  Usually helps a grumpy bike start when cold.

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Just about all bikes sold say new piston. Doesnt mean its new. How hard it it to kick? When you kick it does it stop your foot just as it reaches tdc even if you are kicking hard? Your best bet would be to buy a compression tester (25$ here) because its a pretty handy tool for maintenance. Like I said bofore my ol 87 was low on compression but it ran like a top.

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If all else fails, try going old school.  Lay the bike over on the side for a couple seconds (until gas starts dribbling out the overflows).  Usually helps a grumpy bike start when cold.

This usually works, but I find a lot of people don't know how to use the choke on a 2T - you need to leave the throttle closed, if you twist the throttle open even a little bit you bypass the enriching valve(aka choke). Remember, you are pulling the initial charge of fuel through the crankcase, so it will take more kicks when it has been a long enough period of time since last run.

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This usually works, but I find a lot of people don't know how to use the choke on a 2T - you need to leave the throttle closed, if you twist the throttle open even a little bit you bypass the enriching valve(aka choke). Remember, you are pulling the initial charge of fuel through the crankcase, so it will take more kicks when it has been a long enough period of time since last run.

This could be my problem, growing up on 4 strokes I'm used to giving it throttle when starting.

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