C90Club.co.uk

Hi,
Here's something a little out of the ordinary: I have a Yamaha T90T Japanese Post Office bike, and have 2 issues with it.

Firstly when in top gear, 3rd, it won't change down reliably .
The downshift is vague, with no observable click usually. So when I set off at a junction, i am never sure if it will start off in 1st , 2nd or 3rd.
Sometimes the downshift is precise, with a positive click, but usually is spongy and soft.
Although after down shifting it usually goes into a lower gear, , you never know which it has selected.
Also it won't idle without stalling for first half mile or so.
When engine is warm ,it idles fairly well.

Very little info available outside Japan. T90 was not imported into UK.

Any help much appreciated.
JW

Sounds a bit like my T80, the only help I can give is, wear trainers not boots and learn to count the changes. The gear changes are about doing them slowly, the shaft does not have the slack in the system of a chain so probably the cogs don't release easily. I can have a day when all changes go well and I'm taking my time, another day I speed things up a bit and the odd change goes wrong, it can drop out from 2nd back into first, not nice, or it gets stuck in 4th because I forgot to change it down when stopping.
Wearing trainers or shoes gives you more feel for whats happening and stops you stamping down on the lever, I change into gear early and plan the slowing down changes to end up in neutral before stopping. It does not have the ability to go from top to first at a standstill unlike the later Hondas.
regards
Dave

Hi, many thanks for reply.

The problem I have is that it won't reliably change down even when the bike is parked, and as you say, shifting slowly helps, but only occasionally.

Frustrating!

Sounds like the "cam" is loose on the shift drum if it like most small jap bikes !

Could even be a bent selector fork - caused by numpties jumping on the gear change lever.

A previous owner of course.....

Diesel Dave wrote: ↑

Fri Aug 25, 2017 10:02 am

Could even be a bent selector fork - caused by numpties jumping on the gear change lever.

A previous owner of course.....

Yeah, loads of numpties out there!
My only excuse is that I was trying to change into the 4th gear it doesn't have.

Many thanks for the replies.
How difficult is it to repair /replace shift drum and selector forks?

Could it even be a matter of adjustment rather than repair, or is that wishful thinking?

What I would do is
Strip the clutch cover off you will I think have to remove footrests and exhaust
work the gear change linkage and see what is moving or not the workshop test is to remove the linkage and try the gearbox by turning the selector drum with the nut on the end if box works that way the fault is in the links if not it the box itself Full engine strip
I cannot picture the linkage I guess all Yamaha cub copies are similar but it is a long time since I striped one !

Many thanks for replies.
BTW, is it better to remove the exhaust from the cylinder head when it's warmed up or cold ?

JW

Cold after lot and lots of penetrating oil !