Major Softie wrote:What was the condition of R90 before you did the work? If it was tired, then you are not doing a fair comparison, and don't try to tell me you remember what it was like before it got tired - our brains just don't work that way. The long slow gradual loss of power is something we just don't notice.
If it was running at full stock power before the work, that's different, but the fact is, people VERY seldom do such hop-ups on a fresh motor - at least, in the Airhead world. The Duc people are all crazy: they throw out fresh stock parts all the time

I didn't modify the bike because it was broken. It didn't use oil, compression was over 150Lbs on each side, and it had plenty of pep for an R90, honest. After disassembly I did notice that the crank sprocket was ready for replacement, but no chain slap issues. My main complaint had been pinging and not enough punch while passing on steep uphill grades and the clunky shifting of the old heavy flywheel bikes. Stiffness in my hand on the clutch was another factor. You post 81 bike riders don't know how good you've got it when compared to older heavy clutch pull guys. I'm sure my left forarm is going to start shrinking with this new set up.
Other than that I loved the old motor configuration. It got close to 50mpg with Dellortos.
The ball got rolling when a good used 336 cam fell into my lap for $30.00 and a nice low mile 1983 tranny for less than $150.00. I've always been jealous of bikes with Nikasil barrels, so when I couldn't find an affordable way to make Nikasil 900cc jugs the Siebenrock kit became more and more attractive.