I just bought what I hope is a stock 1984 qt50 and want to upgrade it to eventually be fast enough to safely commute to work. I think that 40mph would be bare minimum.
I have had bad experiences making more than one mod at a time to previous vehicles that frequently resulted in frustration and un-met expectations. This time I will try to only do one performance upgrade at a time.
My first major step, after fixing the brakes and the faulty pet-cock and replacing the air filter with an aftermarket foam thing, will be a carburetor. Based on what I've gleaned from here, youtube, and Mr. Rutherford's site, I think the Mikuni vm20 + mlm intake would work for the long haul.
The one question I could not find an answer to is what jet sizes should I start with considering that the only thing I've done is added a less restrictive air filter?