a65 losing power

[easterndriver]

Hi,
I have a 1965 A65 which has a baffling fault. In top gear and when its opened up it gets to about 60mph then just keeps revving up but the speed doesn't increase. My first thought was a slipping clutch but there are no other symptoms of that. I have just serviced it and fitted a new complete air filter and wondered if it could be anything to do with that. I just cant see it being a slipping clutch because there are no other symptoms. It also backfires when closing the throttle hard which has never happened before.
would appreciate any ideas.
regards colin

[Bess]

Hi,
    I would say a slipping clutch and exhaust leak, mixture becoming lean when throttle is closed, constantly rich mixture or low compression.

Best wishes...

[Allan G]

If the revs are rising and the bike doesn't change speed then it has to be slipping clutch.

Whether the plates are slipping or if the hub is slipping on the taper is the next question. If it's this it can be tight enough to hold until more torque is demanded by the engine.

[chaz]

if its backfiring when throttle closing, presumably on a run, there must be an exhaust leak. with the revs pushing the air though the system, removing the throttle means air outside can enter the cylinder as its at higher speed. a common fault with loose fitting exhaust systems, JApanese bikes have soft asbestos or copper washers that seal, cars tend to use an exhaust putty both keep the system air tight.