TOPIC:

My 1978 kz650c when j was riding it today in 5th gear I was letting the rpms climb higher and higher and all the sudden the power was gone then I let the throttle down a bit and it caught again. It seemed as if the valve springs couldn't contract fast enough, loosing power. This is the second time this has happened. And btw it was not a missed gear because I wasn't switching gears. So why was it doing this? I wasn't even close to top speed.

If your springs are too weak, you'd be getting valve float, which will result in a very different engine sounds and a loss of power.

Getting valve float means redlining (unless the springs are completely rooted) - in 5th gear, that's getting close to 200kph! Valve float will happen in any gear at a certain rpm, you should be able to get the same result in any gear, but at the same rpm. But if it's fine in the lower gears, it would be something else.

What do u think it could be?

How many miles on the bike?
Steve

Like 26,000

sounds more like a clutch issue to me. If you have a service manual it will give you service limits for both. Just out of curiosity, what are you running for oil?

Sounds a little more like fuel starvation.
It would grumble and feel like a soft misfire a little bit first and then the power would just drop out one cylinder at a time over a few moments, until the engine quit using any fuel, then you'd close the throttle down and the carb bowls would fill up enough for the engine to take off again.

kaw-a-holic wrote: sounds more like a clutch issue to me. If you have a service manual it will give you service limits for both. Just out of curiosity, what are you running for oil?

This is my thinking too. Clutch springs are weak.

10W 40 castrol conventional oil. I changed the clutch springs but not the friction plates because they were in spec.

missionkz wrote: Sounds a little more like fuel starvation.
It would grumble and feel like a soft misfire a little bit first and then the power would just drop out one cylinder at a time over a few moments, until the engine quit using any fuel, then you'd close the throttle down and the carb bowls would fill up enough for the engine to take off again.

Ok. Well how would I fix that? I do have the manual.

Where did you say the engine was over-reving in 5th gear, as in slipping clutch? I must have missed that part.

kaw-a-holic wrote: sounds more like a clutch issue to me. If you have a service manual it will give you service limits for both. Just out of curiosity, what are you running for oil?

10W 40 castrol conventional oil. I changed the clutch springs but not the friction plates because they were in spec.