Further research reveals that 70 was also a stock main jet on a towny. Maybe one of my three had a 70 in it. I can't remember.
My QT50 had a 70 main while the towny i picked up had a 72.5. The towny had a fatter needle and it appears the choke port is bigger on the towny as well?? Bore looks to be the same (both 12mm's). Both run the same airbox.
Two of my Townys were white. I replaced both crank seals on the first one but it was always running around 370F-380F. My 2nd one - I replaced just the left crank seal - I could rarely get that one above 340F. A buddy sent me a Towny engine to put a Malossi top end on with a vm20 carburetor. That one ran in the 340's. Must be that 2nd gear taking the strain off the engine.
So 340-380 range is what i should probably expect. I replaced all the oil seals on that motor, so its got good cranky seals!
It did 43-44 with stock exhaust and I could cruise through the neighborhood with the throttle barely open and it's doing 35 in super stealth mode.
I would be happy with 35 (40 would be a bonus). The qt50 engine was hitting 29-30 with a MLM better than stock pipe (the one you sent me), stock carb, stock oil injection, and 60cc chinese kit. I know the MJ50 has a higher end gear ratio and ive sinse blocked off the oil injection. I found out yesterday however that the MLM exhaust does not mount up to the MJ50 tranny as the bigger tranny sticks out to far. I need to either mod it fit (will require hacking) or run a stock pipe. Im debating the stock pipe however the one i have has a series of dents in the header that Im sure are hurting performance to a degree. Im either going to make a new header or looking for a nicer stock towny pipe.
Also, a 15/15 Dellorto SHA fits that intake like a dream. I might just ditch the stock carb and airbox.
I may try to replicate the Dream Towny set up with a little spacing under the cylinder to raise all the ports.
They offer a "power plate" spacer if you dont want to stack 5 gaskets together. Kind of pricey but the quality looks good.