I had the 175cc version of your bike. It was a 1965 Campera and it was a 4-speed. The transmission must have been straight off a trials bike since it had 3 very low gears with a huge jump up to 4th.
Can't help with your problem since mine ran perfectly for the three years I had it so there was no reason to take it apart. I absolutely loved the tractability and torque of that engine and the suspension and handling were top-notch for the time. You'll enjoy it once you get it sorted out.
My understanding was that Bultaco basically made one engine but used different top ends for the different displacements and changed porting and flywheel weights for the different models.
Bud Tugly screwed with this post 02-14-2011 at 08:46 AM