Wait, how can that be true? Yamaha bought Motobecane in 1984. Motobecane have been equipping there mopeds with AV10 engines before that date (as early as 1979). Beside people refer to the AV7 as the American model, cause the AV10 was never available in the US, no matter what moniker it was under. I thought that the AV7 was just a renamed AV88.
In my experience, major breakdowns usually occur when you try and upgrade your top end without lining up the additional performance pieces that are designed to handle all the extra horsepower that your bike is putting out..
For example a Doppler crank is designed to withstand the higher horsepower and higher RPM. So a stock crank will not hold up when matched to a 70cc kit.
The strength of the cam that is attached to the after market magneto, is far superior to the pot metal cam in a stock system.
A lot of people believe you can just buy an AV10 case and your good to go, without realizing that the bottom bracket that is attached to the lower part of the engine is different.
A reed valve engine is more efficient period.