EC250 - Damaged piston or plug?

[JMAN]

Hi,
My EC250 started playing up last time I went out on it. It?s gone through two plugs within about 30mins. Although the power seems good, the bike just bogged down and cut out.

Since I?ve had the bike over a year, I thought I?d check the piston/barrel (see photos). There is a small amount of blow back under the piston and very sooty on the top. The barrel seems fine with no major marks and there is very little play in the bottom bearing. There was however considerable play in the top bearing (within the piston). Is this normal?

Based on the above/photos, please can anyone advise me if this needs changing? Could the plug be fouling up/damaged due to other reasons?

 

[(F5)]

Looks fine, perhaps watch the airfilter (Minor scratches on piston).

I think you have an electrical issue. New plug cap, check the ign coil & lead, hopefully that's it. Obviously use recommended plug.

Check earth for coil & connections. Simple stuff first & hope its not stator burning out or less likely CDI. Hmm, check kill switch too.

 

[Fred1956]

What jets? Piston is black enough that I'd say a bit rich on mixture

 

[pscook]

What jets? Piston is black enough that I'd say a bit rich on mixture

I have read opposite, that a rich condition will wash the top of the piston whereas a lean condition will allow the piston to get hot enough to burn the fuel/oil and carbon up the top.

 

[(F5)]

To be honest I'd be cautious trying to jet from piston colour. Some fuels burn differently, but mainly the best way is a controlled plug chop style; High revs full throttle for a long straight, kill it straight away, pull plug & head if keen. . . . And that will tell you how it is only on mainjet.

But just trailing along & then tearing the engine down, well it could be hella lean on pilot, ok on needle & rich on main,

or viceversa.

Anyway its started playing up, so lets chase that.

 

[Jakobi]

Agree, a rich piston will have more wash on it where a leaner one runs at higher temps which creates the carbon build up. Rich can leave it spoogey though, and as F5 pointed out, your engine can exhibit both rich and lean at different circuits which adds more pieces to the puzzle. The underside of the piston will also tell some of the story. A small carbon spot is ok, if its all carboned its been run lean.

Now, how many hours on that piston? Have you measured the end gap? Nothing looks too out of place that would make the bike run poorly. End gap should be under 0.9mm with .3mm being the tighter end of the spectrum.

Going to have to look at either electrical or dirt in the jets/blocked pilot perhaps.

 

[Vindicator]

I have read opposite, that a rich condition will wash the top of the piston whereas a lean condition will allow the piston to get hot enough to burn the fuel/oil and carbon up the top.

+1 it's my understanding also

 

[Lincolnlock]

Judging by the little bit blow by, the piston looks like it needed to be replaced anyway. Order the top rod bearing also. If the spark plug was wet when you took it out it's probably the stator. They like to stop working after the bike warms up. If you still had spark and the bike wouldn't fire, I would suspect the float was stuck or the pilot jet was plugged up.