Topic: 1972 CB750 clutch tranny question

[tobysdad]

I have a 1972 CB750 with 28,000 miles which has quite a bit of drivetrain lash when riding at slow speeds. Even with the chain disconnected, the sprocket jumps around and jerks like it's out of balance.

The carbs have been balanced, valves adjusted and timing adjusted along with new plugs. All four headers run hot so I don't have any dead cylinders.

I'm starting to suspect a bad clutch and have changed the oil twice. The clutch doesn't slip and seems to pull strong.

I did notice the kickstarter does not slip when the clutch is pulled in. In other words, I can pull the clutch in and kick start the engine. I can't do this with any of my other Hondas (CB550, CB350 etc.)

Is this normal for a 1972 cb750 or should the kickstarter slip when the clutch is engaged?

[scottly]

I did notice the kickstarter does not slip when the clutch is pulled in. In other words, I can pull the clutch in and kick start the engine. I can't do this with any of my other Hondas (CB550, CB350 etc.)

Is this normal for a 1972 cb750 or should the kickstarter slip when the clutch is engaged?

Yes, that is normal for a 750. BTW, welcome!

[tobysdad]

Thanks Scottly!

Well, there goes my theory it's a bad clutch, or maybe it is.

Could warped clutch plates cause a jerky driveline? Like I said, even when I had the chain off and ran the bike through the gears the sprocket would jump around until I pulled the clutch in. Then it would all settle down. The higher the gear the more pronounced the jerking would be.

Any ideas on what might be going on? Thanks

[scottly]

Hard to say at this point, but the chain-off test doesn't tell much. When riding the bike are you lugging the motor? Is the problem only noticeable at low engine RPMs?

[tobysdad]

Hard to say at this point, but the chain-off test doesn't tell much. When riding the bike are you lugging the motor? Is the problem only noticeable at low engine RPMs?

Hey Scottly, No, I'm not lugging the engine. But I haven't taken the bike out on the open road to test as I don't have clear title/registration etc. I've had it up to about 30mph in 3rd gear at the most.

It just feels like a lot of drive train lash as I drive down the road at 20-25mph. I'll feather the clutch and that smooths things out.

It has a new o-chain, properly adjusted, two oil changes, valves adjusted, carbs syncd as best as I can, new plugs, timing adjusted.

It just feels like the transmission is out of balance, if that makes any sense.

It's weird and doesn't make sense.

Any suggestions will be appreciated!

[tobysdad]

Here's a pic of the bike. It's a good one

[scottly]

VERY NICE BIKE!!!! 30 MPH in 3rd gear is indeed lugging it!
edit: NICE BIKES!!!