second melted piston in one month

[proelton]

Hi
I own one ec 125. I allways had 2 strokes since when I was 16 and now I am 26 and I know pretty well how to jet the carburetor, read spark plug and so on, including ride it. not that i am better than you im just telling im not a new guy on this subject.

However I am having one problem with my ec 125, which i bought 2 months ago. The bike is very explosive and fast, but since i started to ride it harder, I lost 2 pistons. One melted around the piston crown close to the rings (stronger melting near the exhaust port) and stopped working. No major damages to the sleeve or cylinder. I only changed the piston and it was ready to race.

The second piston, which I run the second ride last weekend (tough riding with lots of high rev as I always ridden my previous YZs 125 and 250), is showing the same symptom of loss of power, no high rev and very poor low end. I almost cant go up normal road hills. Im sure this piston melted too.

What do you think it is?
May it be low quality piston?
may it be that it needs one nikasil treated sleeve to work propperly on high revs? I think it is with chrome sleeve.

The Carburetor is jetted right.

I need suggestions, please!

Thank you!

 

[GMP]

Where are you located? You say your jetting is correct, if your fuel has a lot of ethanol have you jetted for it? What are your specs?

Other than that, fuel starvation (lean) at high revs from delivery problem. Are there any lean symptoms? Check the tank vent in the cap, they can stick/swell(rubber seal) and cause enough vacuum to starve the motor. My 250 just died on a road but I can see where a smaller motor (less fuel demand) may just run lean. Remove the rubber seal and plastic cup. Enlarge the holes on both and reassemble. Also don't use an external check valve.

Air leak? Check with starting fluid.

Ignition timing?

Start here and let us know, good luck.

 

[stainlesscycle]

One melted around the piston crown close to the rings (stronger melting near the exhaust port) and stopped working.

if the front half/top of the piston is destroyed, it's usually ignition timing. but it wouldn't be melted - more like eroded.

did the motor ping, or get abnormally hot before it melted?

The second piston, which I run the second ride last weekend (tough riding with lots of high rev as I always ridden my previous YZs 125 and 250), is showing the same symptom of loss of power, no high rev and very poor low end. I almost cant go up normal road hills. Im sure this piston melted too.

this shows it is not ignition timing.

check the reed cage?

are the piston/rings sized properly?

 

[iajim]

At this time you may want to start at "ground zero", check the timing, jet a little richer and take a look at the cyl. head. See if there are any, even very slight imperfections in the combustion chamber, a nick or deep scratch can create a hot spot leading to pre-ignition. Usually any jetting problems will show up on the side of the piston, where as (pre)-ignition, low octane fuel or too high compression will show up on the top of the piston. A switch to 50/50 race fuel/ pump gas might be in order to give you, your piston anyway a measure of safety. I hope this helps and not just confuses the problem.

 

[Diddel]

Ignition side crank seal?