When I put the main belt on, the manual said to keep the long side tight, and after I slid it on, and let the tensioner down, i checked tension by pulling on the middle of the belt where the manual shown and measured deflection. IT did seem like it wasn't tensioned enough when i was tugging on it, but it measured OK with a small scale (at the upper limit, but still within bounds).

I'm not sure what you mean that "The belt should just rotate a little past 90 degree on the long side".

Both belts went the first time, I thought that the balance shaft belt may have took out the timing belt, then though. The second time this happened (after 30 seconds of running), the balance shaft is OK, but the main belt stripped at the crank.