etz 60mph sieze

[stickman]

Hi.
I have an ETZ 150 '85 but not used it much since getting it 2 years ago. Had a few jobs needed doing and I dragged my heels but got most of them sorted recently.
I took it out for a longish test spin recently and the back wheel locked up at 60mph on the motorway. I clenched. Luckily not much traffic and I was traveling in a straight line so skidded to a halt.
Cant remember if I pulled the clutch in or not while skidding. I got it started after a dozen kicks and a bit of pushing and I gingerly rode it the 20 miles or so home at about 35mph.
It worked ok the time before that on a few short runs but the time before that it seemed like the piston had locked up a bit also but not so severely. Felt as if wire was wrapped around the back hub. Again I drove it the mile or so home slowly.
I thought after the first time maybe the mix was too lean at 50:1 fully synth. So I changed it to about 30:1 semi synth thinking it would solve it.

Any thought's would be much appreciated. Don't want to risk it happening again. Might not be so lucky the next time.
JC

[arry_b]

That pot's got to come off for a look at the piston and rings. What you don't want to happen is for the piston to break up and take out the bottom end of the engine.

As to the cause, it won't be due to the petroil mix proportion, they run fine on 50:1 when they're in good order.

First thing to check is points gap and ignition timing. Then go through the carb settings with a fine tooth comb, and check the air filter element is in one piece and clean.

There's a long skid mark on the M50, left bymy 251 when it did the same thing - it was the carb in my case. You can tell when the bike is about to seize up, it's about two seconds after you think to yourself that the bike's going unusually well!

[stickman]

Grand job. Thanks for the info. Will work through the list.