I bought a Model 18 in March which is a joy to ride, sweet gearbox, marked GB2 KS11. However on a ride the gear change lever wouldn't return to the 'home' position. This was quickly traced to the leaf spring being broken. I rang the spares company and order a replacement and asked for all the seals for the outer cover, it turned out I also needed a gasket, a previous owner had use Hylomar and no gasket. Now the problem..... After completing repairs, pulling up a hill so with additional load, the bike feels as though it is trying to jump out of gear, a sort of lurching sensation. Adding the gasket has moved the outer cover away from the body of the gearbox so I'm wondering whether the thickness of the gasket has caused the selector drum to lose indexing (for want of a better description!). I'm not sure whether there should be a spacer on the selector drum shaft where it comes in contact with the bush in the outer case, hard to be sure from the drawings, currently the selector drum is in direct contact with the bush (no spacer). When the gearbox is assembled, with the gasket, I can detect about 1mm of end float if I pull and push on the nut that retains the gear position indicator.
My second problem is self inflicted. The carb on the bike is stamped 835, it's a monobloc but I can't find 835 as a part number, only 839? There was far too much slack in the throttle cable so I set about replacing it. I didn't realise there was no circlip on the needle so didn't note which groove the clip was in. If someone can tell me which groove from the top is typical that would give me a starting point. Not sure if it makes a difference but the bike has a competition engine. I opted for the middle position as a starter for ten.
At this point someone tells me the lurching is caused by the wrong needle position, not the gearbox
)Thank you in advance.
Chris.
