Many, many years ago, I owned one of those little Jawa's.
They reach 45 ~ 50 km/h (28 ~ 31 mph) even carrying two adults.
Up-hills were not problem in second or first gear.
I would pressure test the crankcase, those crankshaft seals are probably too hard to prevent leaks (worsening performance at low rpm-wide open throttle).
I would verify the transmission for all gears by turning it by hand.
These little engines are more sensitive to poor rings-cylinder seal that to off-timing.
lnewqban screwed with this post 01-08-2013 at 06:53 PM