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Wots goin’ on here pls folks?

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Lobo:
1/2 pistons scored down one side of a 250cc 2-stroke, which runs on 100:1 premix. The rings are seized into the grooves at this point.
Salvageable? (not too fussed about performance, but need reliability (outboard motor).
Why the damage so localised?
Little / big ends all seem good, as are crankshaft bearings...
Ta,
Simon

adespin:

 I wouldn't be running a 2stroke on 100:1, i run my chainsaws on 40:1 even though recommend ratio is 50:1

McCabe-Thiele (Ted):
Looks like straight localised overheating to me certaily more 2T oil as well as possibly considering change to fully synthetic brand would not hurt.

If it's a little used motor then fuel degredation might also be a factor with degraded fuel combustion products causing raised burning temperatures. Do you drain it right down and replace with fresh fuel when its out of use?

Is the recommended 2T ratio really that low certainly an increase will help in my opinion downside of too much oil is obviously more frequent decoking and plug fouling?

K2-K6:
Lubrication breached, obviously!  But reason is important to correct.

As others, is it really supposed to be at 100 to 1?
Presumably water cooled?
Have you pictures of combustion chamber, piston crown and spark plug to see colours.
What is the spark plug identification/grade etc.
Looks like exhaust side of piston?

Lobo:
... it’s a ‘new’ motor to me; and 20yo I guess. 100:1 is the correct mix, and indeed that sticker remains on the side of the engine.
Yep, water cooled - though now apart its arteries are seen to be a wee furred up and will be corrected.
The piston crowns indicate a slightly rich burn, as do the plugs, but tbh it’ll only run on choke at the mo (or throttle) -  hence the tear-down.
Nothing looks horrible in there ....
All the ignition components / plugs now new, the carb galleries & jets cleaned through to an inch of their lives, float level ok, Reed valves look &  ‘feel’ ok, and yet it continues to die if idle drops below choke-on speed, accompanied with a lot of shuddering & the odd back fire.
I’m kinda at last resort, and will change all the crankcase gaskets and seals; the piston issue is unexpected and new to the problem.
....if (unburnt) gases are leaking past the seized piston rings would this cause the no idle & backfire?

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