I have a 1976 Honda mr250 that I got on a trade and it had low compression and I put a new piston and rings in it with a .40 over bore. And I also rebuilt the carb with a rebuild kit I purchased off of eBay but I believe the main jet is a little bigger then stock on the one that came out of the carb itsaid 110 on the top and the new one that came with the rebuild said 140 on the side or it assuming those are the sizes of the jets? Anyways I got it all back together today and used the gas my dad has for our trimmer that is mixed and it started right up and right fine just needed to be tuned a little it bogged down but I didn't want to mess with it I just wanted to ride around my yard sense I finally had the time to get it back together. And I have bell ray 2 stroke oil (it says power valve formula on the top I know my bike doesn't have power valves but will that make a difference?) and I mixed a gallon of gas with 4ounces of bell ray oil (32:1 ratio what I found on another thread on here that worked good with these bikes so that's what I used) and now with the new gas it will start but won't stay running and it sounds like it's either misfiring or back firing really loud I tried adjusting the air mixture screw up and down both and it didn't make a difference. Any help would be greatly appreciated it's really frustrating me and would like to fix it. Thanks!!!!