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97 yz250 wont start, AT ALL!

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Ok this guy brought me his 97 yz250 in pieces. The motor had been slapped together but I went through and torqued everything to spec. No leaks, great compression and carb is clean as a whistle and its getting fire but it won't even begin to start. What am I missing?

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Ok this guy brought me his 97 yz250 in pieces. The motor had been slapped together but I went through and torqued everything to spec. No leaks, great compression and carb is clean as a whistle and its getting fire but it won't even begin to start. What am I missing?

 

Fire as in a thick blue spark? A deteriorating stator, coil or CDI will still sometimes weak spark. Or drop of at operation temps.

 

Have you verified timing?  

 

What do the reeds look like? Sealing?

 

When you kick it do you smell un burnt fuel? Wet spark plug?

Edited by UncleLuke
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Spark may be the problem it dies look a little weak but I've had bikes before that ran on less spark. The reds look fairly new and are sealing. I do smell sunburn fuel and the plug is wet. I actually just looked at the timing but I idnt do enough to tell if it was off. I'm thinking that is it. Do I really need any special tools to set the timing?

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A dial indicator and a way to mount it into the spark plug hole certainly helps with timing. I made my setup for $20 and 5 minuts of drilling and tapping.

On my '97 yz250, there's a line on the flywheel, a line on the stator and an arrow on the case pointing towards the stator. When my timing was set perfect per the indicator and manual, all of these lines and arrow were lined up. You have to look under the flywheel while the piston is at TDC to see the stuff I'm talking about.

Edited by Thinlineggman

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Timing was off by a fraction. I set it to spec and got a couple pops out of it then nothing. It's getting fuel. Getting spark and air. Has plenty of compression. I also didn't mention. I don't have the silencer on it yet just the headpipe. Could that make the difference

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It should still run but it will def be harder to start. 

 

Not to ask the obvious but have you replaced the spark plug? If it was fouled it is no good.

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Timing was off by a fraction. I set it to spec and got a couple pops out of it then nothing. It's getting fuel. Getting spark and air. Has plenty of compression. I also didn't mention. I don't have the silencer on it yet just the headpipe. Could that make the difference

You're not setting it to .007" from TDC are you? This year bike requires the timing marks to be lined up at TDC according to my manual and my running bike.

And no silencer = reduced back pressure, and two strokes like some back pressure.

Broken reeds will also cause hard starting, so check those if you haven't yet.

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Ok got an update. I put the silencer on and tried kicking it a time or too. Got a few more pops out of it but still no crank. I pulled the reed block and found that although the reeds look new there's a hairline gap on both of them. Could this be my problem and how can I correct it?

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Should still run with a tiny gap. To fix it, buy new reeds. (I got rid of the whole stock reed assembly and got a boyesen rad valve)

Is the kill switch stuck? Try disconnecting it.

Also, throw in a brand new spark plug that is one step hotter (br7es NGK) and give it a shot.

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