I assume you mean the wrong mixture ratio rather than wrong type?
If the mix was too weak then effectively the engine is now scrap as you have more than likely lost compression due to a smeared/scored piston and barrell.
If you've over oiled the mix and it won't start, try removing what remaing fuel you have in the tank and re-fill with the correct mix. Remove, dry and clean the spark plug, clean the air filter and if possible remove the exhaust. Then try re-starting.
pleasant, September 2011
