Possible old two-stroke oil in the crank shaft area

[Robertsrg500]

My 1986 RG 500 gamma sat for a year and a half with oil in the tank and the fuel petcock open. missing spark on cylinder three and when I check with the spark plug tester all four are firing replaced the coil replaced the CDI and when I pull that plug out it’s totally green with two-stroke oil is it possible I need to flush out the crank and sipon through the rotary valve disc covers rather than turning the bike upside down I think I’m on the right track any ideas. Plugs are new. It’s also now starting to miss on cylinder one which as the bike leans to the left on the side stand could be contributing factors?

[tonyhes]

I have no idea what I'm talking about. I'll just say oil check valve? Excuse my ignorance.

[tacky1]

Turn the engine over with no plugs. Blow it out. Then ride it. You need to fit check valves on your oil lines. Plus I would strip the carbs. Clean them. Check the float heights and more than likely replace the needle valves as they are shite. Well know that they leak. Replace them with the ceramic valves.

[phildu31]

First post, not even a "Hello" ...
You're lucky to have 2 answers.