an o.s. 46 should run just fine inverted if tuned properly. what i do with mine is use a idle bar glow plug so not to quench the plug with excess oil and fuel and make sure your tank isnt higher than the carb. this will allow the fuel to syphon into the carb and allow more fuel into the motor than is required. if you cant lower your tank then put a loop in your fuel line leading to the carb. if it still doesnt run properly then try a glow driver. all of this in-which im telling you worked for me. glow driver is the last resort and sometimes required. let us know will ya.