1995 yz250 won't start.

I bought the bike a few weeks ago and it was barely ridden the thing looks brand new. I've ridden it about ten times since then. I have fouled a couple plugs. 32:1. I'm new to the two stroke thing. Well when I was riding today it was running good and then it fouled a plug and wouldn't start. So I put an old plug back in and it fired right up. Rode around for about an hour and on the way back it started bogging like crazy like it was running out of fuel and died. I cannot get the bike running again. I got it home and pulled the plug out and set it against the head, and spark is present but I'm not sure if its strong enough? Removed the carb and checked the reeds they look good. Pulled float bowl off and cleaned it out, there was se gunk in there. Sprayed jet out and blew air through it. Checked floats and they seem to be working fine. Carb is getting fuel from tank fine. I am stumped. Any ideas would be appreciated!

Is the jetting right for your elevation? Is the spark plug wet?

You have spark, check that off.

Sounds like you have a fuel starvation issue. Since the bike is new to you, I would flush the tank GOOD! Take off the valve and take apart and clean, replace fuel line.

Carb: Take out jets, clean EVERYTHING. Blow through all passages. Document jets. Make sure that the needle and float move freely and the needle will shut off and open freely. Take your time, get 2-3 cans of carb cleaner from China Mart (walmart). Make sure every little hole in the emulsion tubes are clean, all jets clean. Eliminate carb possibilities. DOCUMENT EVERYTHING!

Did you pull the reeds out of the jug? or just look in? Go ahead and take them out. Make sure you can't see light though the block so they seat tight!

While you are in there, take a look at the cylinder and piston. Look for wear patterns.

Deal with carb and then move on to other things. It is a game of eliminating variables. Document everything, can't stress that enough. It will come in handy later.

Get a few extra plugs till you get it jetted the way you like. I think B8ES will fit, check to make sure. No reason to get the good plugs till you get it figured out.

Lots of good people here to tap, Got questions?? ask these guys, they are great! We help everyone and each other.

Welcome to the club! Stay with name brand oil. There are some good ones out there. 32-1 is ok. Better to foul the plug once in awhile rather than fry a motor.

Let me/us know how things are going.


I heard a thread similar. And it was the power valve not opening. A retaining pin broke.

I pulled the reed cage out and the reeds look fine. I will pull carb apart again when I get home and clean it again. And I will put a brand new plug in just to be sure. And yes, the plugs get oil fouled. My friend is new to riding so I think they get fouled when I can't stay in the powerband or ill leave him in the dust. Can someone explain the function of the power valve to me? It might be worth checking out

Basically out opens up the exhaust port wider for more flow/power

As the motor rpm raise the power valve opens more. This is were the other guys pin broke. from what I remember, pulled the power valve cover off (above the water pump). Started the bike and gased it and watched to see if the control arm moves.

Alright ill check that out also. Makes sense. Just seems weird that I can't get the bike to run at all now. When I get home I will drain all gas clean the carb out again and check the power valve. Ill let you guys know how it goes. Thanks.

Turns out it was just the plug. Guessing when the plug was under compression pressure the spark was too weak. Put a new plug in it and it started up on the first kick like always. Thanks for all the help. Runs a little better now that the carb is cleaned out it seems. Time to rejet soon!

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