Honda c90 cub is jumping out of 3rd gear usually above 30mph. Probable cause?? Possible solution???

Question

bike jumps from third to second and engine revs to max. i can only kick it back to third when the revs drop off. this happens frequently but intermittently and without warning which makes it extremely dangerous in traffic.

Answer 1

Just possible that the drive chain in very tight and is straining the gearbox output shaft. If that isn't it then it's an internal gearbox fault. Might be bearings, might be the selectors

Answer 2

shift fork

Answer 3

Check the Shifter mechanism,,the detent in particular.

There's a few more things to transmissions than Shift Forks,

thus a few more problems occasionally arise than Bent Shift Forks.

Jumping OUT of 3rd is one thing,,,,jumping TO 2nd is a whole 'nother matter

You can inspect and repair the shift mechanism via removal of the clutch cover,,aka r/h engine cover.

Possible there may be internal damage,,

but I wouldn't even consider that possibility until proper condition & function of Shift Mechanism was positively verified

Good Luck

Answer 4

Quite possibly the selector fork in the gearbox is knackered - bent likely. You say it only happens in 3rd so it is unlikely to be a common component on all the gears. Not great news if it is this as it will require and entire engine strip to examine it. On the plus side these things are as easy to work on as you can just about get.

Answer 5

Chances are it's a worn/broken selector fork or possibly selector drum. You ought to be able to get one easily enough but it requires splitting the crank-case to fit it.