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81 cb750c Starter Clutch Issue


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I have an 81 cb750c that is giving me starter clutch issues. The Bike is new to me and has about 3.5k miles on it. When I would go to start it I would get a high pitch whirring, with no engagement. After slowing down it would sometimes clunk and then the next time I hit the starter it would catch for 1 second to long enough to start. I bought a rebuild kit and rebuilt the starter clutch and at the time it made a noticeable improvement but did not solve the issue. This was in the summer when it was 70-80 degrees out. Now with the cold in the winter, anywhere from single digits 50 degrees it slips a lot more, basically back to how it was before I rebuilt the starter clutch. Once the bike gets up to temp it engages more reliably and only slips one out of every 5 cranks.

What could be the issue? When I took it apart I didn't see much if any wear on the gears. I saw some post saying that the surface on the gear where the clutch rides could be worn but I find that hard to believe with such low miles.

Oil is also what is recommended in the manual, forget the weight atm but I know its conventional.

Edit: I took the cover off and it is definitely the starter clutch that is slipping, just don't understand why.
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The rollers and internal housing of the starter clutch most likely are wornnnout very common prob on these bikes also check the bushing in the center of the starter clutch gear itself as mine was wiped out reb hold kits go for 60 to 90 bucks on the bay or some people up date them with better built multi roller 8 I think yamaha r 6 starter clutches but u gotta d9 some drillin
I have also fixed my several times over the years.
I have read online that the bolts loosen up over time and then you have the problem again.

You can use blue (I think) Loctite hen reassembling and it should last longer.

That is why I decided to try the starter clutch out of a Yamaha R6. There are videos on Youtube but either I bought the wrong part or it doesn't fit my 1981 Honda CB750K. I checked and I seem to have the correct part number.
The Yamaha starter clutch is a better design and works great. I know from experience - Do yourself a favor and retrofit the Yamaha stater clutch.

What Yamaha part number did you get? What year Yamaha R6?
I have a 81 Honda CB750K is that the bike you did this upgrade on?

Thank you,
I bought the following Yamaha part;
Is this what you used?

New FZ6R R6 R6S Starter One-Way Gear Assy. 5SL-15590-00 For FZ6 YZF6S YZF6​

Amazon $58.00

It does not seem to fit???

Thank you,
I did it on a 1983 Honda CB1000 but the CB750 uses the same part so the Yamaha starter clutch will fit you do have to drill / modify.

Here is a video:

We rebuild them to the modern style sprag type clutch to replace the three roller Style the outer cover is redrilled loctited... it will not need retourqing


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I did it on a 1983 Honda CB1000 but the CB750 uses the same part so the Yamaha starter clutch will fit you do have to drill / modify.

Here is a video:

I’m trying to do the R6 upgrade on my CB750 Custom but the fit is very tight. I think with the engine running it will spin the starter gear. Any ideas? Thanks
it's a great upgrade - no more starter gear slippage. you can always clearance with abrasive materials if concerned about tight fit!!