If the rest of the gearbox is working properly, removing the detent plunger will not cause or allow it to go in more that one gear at a time. Taking the detent plunger out will mean that you might have trouble getting the shift mechanism to work normally. There are many other possibilities for why the crankshaft won't rotate though. A good way to work out why the crankshaft won't rotate is to take the engine covers off. That way you will know if it is one of the many causes external to the gearbox that is causing the problem
Just had another thought. Check for "poling". This is where one or more magnets touches the stator laminations. Can be caused by play in the main bearings, poor alignment of flywheel on the taper, loose stator screws, loose magnet/s
I'm not familiar with a techno flywheel so can anyone say if it is feasible that the cup of the flywheel has moved relative to the hub of the flywheel?
Another thought was is it possible that the magnet that triggers the spark may have lost its magnetism somehow and so the spark is being triggered by the wrong magnet?
I'm pretty sure that inside that hollow "bolt" is a spring loaded plunger that holds the shift drum in the right spot for each of the gears. There is a cam on the shift drum with multiple indentations, one for each gear. Normally there's a copper washer under the head of that "bolt" to seal it. If you want to pull it out to fix the leak, you can pull it out and put it back in without causing any problems with the shifting mechanism. The plunger and spring will be able to fall out of the "bolt" though. May need to take the swingarm out to give clearance to get it out or maybe not. I have only had that "bolt" out with the engine out of the bike.
The black circle is a bung fitted to seal a manufacturing hole in the gearbox casing. The hole is there to allow the casing to be machined to provide the left end bearing for the shift drum. There are no rolling element bearings on either end of the shift drum. Provided the crack doesn't allow misalignment of the shift drum, it should be fine without a weld repair
Yes the one on the left seems to be the only one that cracks. One TY175 I bought has a triangular 6mm thick gusset there (goes right down to the junction of the frame tubes) and for what it is worth has no tube cracks at the upper ends of the gusset. The bike I'm referring to has cracks in the front uprights so it has probably been ridden very hard
If the existing carby mount attaches to the head with two studs, you might be able to use a (flange-mount) pit-bike carby. It would require a flat isolator and longer studs
That looks like a carby made specifically for a manufacturer for a particular model bike so will not be available new from Mikuni. It would be helpful to share what motor the carby came from.
My epoxy linings went dark brown after a few months exposure to petrol while the original polyester resin stays clear/light brown. Also a 40 year old unlined Spanish fibreglass tank will usually have exposed glass here and there.
