yamaha wont run

[beyonder]

I purchased a yamaha 175 recently ran fine until it back fired and quit have been able to start it. I have fuel and spark, heres the kicker i found out that the oil line wasnt mixing with the gas. I am green when it comes to bikes, but the guy who sold it to me said i probably blu out the rings. The motor is not ceased, i checked the plug was fouled with gas, since finding out that the oil wasnt mixed right with gas measured some into tank. What else should i do or is it a major job to change out the rings on the piston.

[beyonder]

have not been able to start the bike.

[matt bristol]

depends on how long you ran it without 2 stroke - I'm assuming its a 2 stroke - as you could have killed various different or all parts of the engine. Main culprits failing due to lack of oil will be main bearings, big end, piston/rings/bore wear.
Easy way to check if the bore is worn (therefore reducing compression) is to pour a little petrol down the spark plug hole, quickly get hte plug back in and try to start it. If it fires up this way but not without then it is likely the bore is worn.
If it fires up with a fast long tow start but dies at low revs this is also potentially the bore worn or could be big end - if it sthe big end you usually get a knocking/bag of spanners/grinding noise too
Two strokes are fairly simple to strip and rebuild, if the engine is broke, what do you have to lose by stripping it? (after trying the above of course)