Good Morning CRM fans,

Would someone be able to compression test their bike when cold for me? I've done a rebuild (no rebore) because the compression was at 120 but after the rebuild I'm only getting 125?

I don't know what mine was putting out when warm as I replaced the piston due to it not running and it still won't start.

Have you turned the fuel on to help seal the bore? I understand you have other issues with the engine.
Is there a decent spark?
Is fuel getting through to the combustion chamber?
Mike

Just whipped the plug out of my AR and done some testing for ya.
130-135 psi (Fuel off)
150-155 psi (Fuel on)
Both tests at WOT and engine cold.
Fresh top end (bore,plate, piston, rings, bearing) just run in.

Thanks gents. When the fuel is on I'm getting 125 so seems low compared.

Why didn't you do a rebore?

There wasn't any scoring so didn't think it would be necessary. Should I have?

It's not necessarily scoring but wear. You should have measured the bore. BUT to be honest if you are replacing the piston and you have low compression you should have had a rebore.

Yeh I'm wondering whether it's the wear that's causing the low compression. To be fair I did take it to a bike garage and the guy just told me to get the same size piston that I had removed.

One more question, so the compression is about 125 cold. I know that's low but wouldn't it still start but not produce very much power? Mines not even hinting at a start

should still start I would say.
Need to check a load of things now:
Fuel getting to cylinder
Spark
Reeds (should still run unless non existent)
Timing (some have had woodruff keys fall out/shear meaning the rotor turns on the shaft)
That's about it really

Yeh it's weird. All of the above are fine. I've fitted a new dep pipe aswell. It replaced an old dep pipe so it shouldn't need rejetting should it?

nope. when did it run last? did you try a bump start?

how old is fuel?

I stripped it diwn this time last year, painted frame etc,fitted exhaust. Bike started fine but was running badly,bogging down when I tried to rev it. Was trying to sort that when it just cut out and I haven't been able to start it since.
Fuel isn't too old, I put fresh in after I had rebuilt the bike.
That's when I replaced the piston thinking that was the issue but still no joy.
Spark us fine, plug is wet when I do try and start it.reeds are fine.carb is clean as a whistle.

crank seals? you should do a leak down test really to check!
https://www.duncanracing.com/TechCenter ... sstest.pdf