Stock 1995 Honda CR125 top end issues and questions

[Evan York]

All,

After sticking my first piston, I cleaned up the cylinder with muratic acid, and KartSport took a diamond hone to it. They seemed to think that it was saved and good to go...so I did a complete top end rebuild.

It fired up on the first push, break in was smooth, and seemed to run pretty solid. It was cooler out, but I ran a safe jetting setup in my PWK AirStriker Carb: 180 main, 58 pilot, DGK needle #3 clip.

I ran for most of the day and was pleased with how it was running. I don't have a ton of experience with shifters yet, but it seemed like it should have pulled harder. Perhaps a jetting issue??

Anyways, here's where my main story begins: On one of my later sessions on track at MMX (after maybe 35+ laps), I noticed a quick "burp" under power. This occurred just before pit entrance, so I came in. It continued to run until I got to my pit area. After I had cut it off, I noticed it was slightly low on fuel, but I didn't think it would be low enough for an air pocket to get in the fuel lines (fuel level was above the neck on the lower part of the tank). So I threw more gas in it (6oz Motul/1gal 110 VP Race Fuel), and tried to fire it up. But, it would not fire....

I tore apart the top end, and this time the ring fused to the piston itself...no apparent damage to the cylinder. Tim Pappas took a look at the cylinder, and said the port's edges were a bit round, and could have caused the ring to fuse. So he suggested a cylinder repair (which I should have done in the first place...). Millennium Technologies is sending my cylinder back currently, and I hope this is the last of my top end issues.

After doing more research, I could have a number of problems, however. Here's what else I think I could be having an issue with 1) an airleak or 2) ignition timing.

My problem: I don't have tools to test an air leak. And I'm unsure of how to check for a bad CDI or stator. Any further suggestions?

Thanks in advance!
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Regards,

Evan York

www.evan-york.com

@EvanYork

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"That which you manifest is before you" - Enzo the dog

[Vernon Head]

You could have a leakdown test done at your local kart shop. If it were me, I would fix the cylinder first and see if that works.

[Sanford Mitz]

On a CR, its pretty easy. Go to the hardware store and get a pipe plug for the exhaust and one for the intake book. Swipe the hose off of a compression tester with a spark plug fitting. GENTLY apply some air and listen. You can also spray soapy solution, etc on the base gasket, head gasket, etc. You can also buy an inexpensive leak down checker. Just be gentile with the air so you don't pop out a crank seal. This will be a good investment for you. Sent an engine builder of a picture of the bubbles on the base gasket once. The engine had just come back from a rebuild. This saves a lot of track aggravation. Once had a Pavesi leaking through a stator bolt that was over drilled.

[Sanford Mitz]

There are a bunch of nice leakdown checkers on Ebay for $35-$60

[Todd Kageals]

Evan,

I blew my '94 CR125 down at MMX too! Must be something in the layout of the track!! Kidding....I'm interested in what it cost for a cylinder repair (was that a replate or sleeve?). I priced a re-plate and a new cylinder was just a few dollars more so I bought a new cylinder for mine. I'll be back down there soon. My issue ended up being a lower rod bearing that was coming apart. Actually, the engine was still running. The ground wire for the coil broke and killed the motor on track. After repairing the wire, I went to start it and it would not turn over. Found metal pieces in the exhaust and the rod was locked up. Good luck with yours.....I have just finished my repair and plan to get down to MMX as soon as it warms up!

[Chris Reinhardt]

If it were ignition you would see some deto on the piston...

If it were an air leak, your baseline jetting would be off...

Biggest cause of air leaks in a CR125, the seal under the stator... Pop off the stator and see if there's dirt around the seal. That's the biggest tell tale, but I would swap it out regardless.

CR
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[Enzo Iadevaia]

Ring fused.. Top ring land of piston got hot and expanded and the aluminum smeared down and locked ring up in groove.
Your either to lean, not enough clearance, or overheating.

I've learned over the years that's it better to have too much clearance then not enough.

[Jim McMahon]

If its the cylinder I am thinking of, was it not cracked at the exhaust bridge? It's not a leakdown tester you want BTW, its a pressure tester to make sure the crank seals and other gaskets are sealing.

http://www.duncanracing.com/TechCenter/2stk_presstest.pdf

You can do it with a couple of tools from harbour freight. Ideally do a pressure test and a vacuum test.
That said, it doesn't really matter if you have a crack in your exhaust port bridge.
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[Tim Pappas]

[Brian Fisher]

[Chris Reinhardt]

[Tyson Henry]

Yeah, a brand new 99 cylinder can be had for ~270 to your door. Not sure what it costs to get a cylinder fixed, but it can't be much cheaper than that after all the shipping.

[Todd Kageals]

Yep.....that's why I bought a new one instead of replating my '99. Was within a few buck of replating so why not get a new one???

[andy graham]

$270 shipped? where from? I need one...also need an 85 stocker

[Tyson Henry]