EC125?05 non start/no idle

[mack]

I recently bought the bike with a broken piston and cylinder, I fitted a replacement cylinder and a wossner piston kit.
started the bike without any problems, did a 20min break in of the new top end without any problems.

last weekend I took it for a ride in the forrest but after 10minutes of riding the idle disappeared and I stalled the engine, it did not restart with the kickstarter but I was lucky enough to stall it on a hill so I then managed to bumb start it going downhill.

now I noticed there was still no idle but it ran as long as I kept my hand on the gas.
I immediately suspected some error in the carb, I took it apart when I got back and did not find any faults with it -- put it back and tried to start the engine again -- did not start with kick starter but with a bump start it started (exactly the same)
when i pin it, it revs good and the power is good.

next step I did was swap complete carb from a CR125 and fitted a new spark plug -- did not do a compression test but it "feels" good.
I visually checked the reed valves, I cannot see any cracks or chips.

after this the symptom is exactly the same only start with a bump start and no idle.

My suspicion is now incorrect ignition? (but I guess if this was the case then it would not start)

or reed valve fault? (shouldn't it lack power on top, and visually se the fault)

Im running out of ideas and starting to regret that I bought it.


I have attached a photo of the flywheel when the piston is at top, maybe you guys can tell if it seems OK?

Im grateful for any suggestions.

 

[Fred1956]

Check your compression, it ran right after the piston install.

No kickstart + the fact that it WILL bump start is classic low compression symptoms in my experience. There are other things- broken reed valve etc

 

[adv rider]

no start

I agree on low compression. The original piston was broken, how were you sure that you got all the piston pieces out of crankcase? I bet a piece went thru piston,and is causing the possible compression issue.

I ask this based on my experience from many years ago with a cr80 and small pieces left stuck in rod big end, then going thru piston when running. Went thru 3 pistons before realizing needed a complete teardown.

And if piston blew up, the lower bearing may be failing too, most likely- sending shards through top end

 

[GMP]

Yes check compression, but also check PV to see if it is stuck wide open. Stator is also a possibility, looks like ignition compartment has seen its share of moisture by the oxidation on the flywheel.

 

[mack]

thanks for your input, I will get a compression gauge tomorrow and check it.
fingers crossed its not destroyed cylinder or piston :-/
If compression is OK then I will remove the flywheel

 

[adv rider]

no start

It would be a good idea to find somewhere to borrow a leakdown guage. You can remove the exhaust and reed cage and take a look at the piston too, if unable to get it to kickstart.
Then you can see if anything went through