Topic: Feels like slipping clutch(but it’s not)

[lash]

One of my 69 cb750 is giving me grief and I need opinions. If I hold steady at 4000 rpm as an example the bike lurches like the clutch is slipping, but I replaced  the clutch and basket with a new one and no change. Carbs have been checked, cleaned and synced. Only thing left I can think of is electrical. I am not seeing any sparking at the points, it is timed correctly.
I am not an electrical genius so any suggestions would be greatly appreciated.

[newday777]

Sean had a similar problem when he arrived in New Hampshire. He thought it was the clutch too. He pulled it apart and everything was in spec with the clutch. Readjusted and still had the problem. Andy750 sent a message that he had a similar issue in Austria going up a mountain. He found a loose screw on the shifter drum end in the shifter/transmission cover.
I noticed a rattling in the shifter side while I was there shifting the bike at idle on the centerstand (and wondered if something was amiss in the shift linkage)
Sean popped off the tranny cover and sure enough that screw was loose on his. It was allowing the shift linkage to not shift fully into the gears. We cleaned up the threads on the wire wheel, put some blue loctite on and tightened it up. As far as I know that fixed it still.

[BenelliSEI]

Hate to suggest the obvious but checked the drive chain? I had one with a weird tight spot and when it lined up the sprockets just right it gave the strangest sensation right through the bike (I thought it was clutch related). It would also do it occasionally when setting off from rest!

Showed up when up on the centre stand and I was spinning the rear wheel. After a few revolution it suddenly almost stopped turning and needed extra force to rotate.

[newday777]

Hate to suggest the obvious but checked the drive chain? I had one with a weird tight spot and when it lined up the sprockets just right it gave the strangest sensation right through the bike (I thought it was clutch related). It would also do it occasionally when setting off from rest!

Showed up when up on the centre stand and I was spinning the rear wheel. After a few revolution it suddenly almost stopped turning and needed extra force to rotate.

👍

[M 750K6]

I'm having problems with my ignition key switch. That can give the surge, lurching sensation. In neutral, key at 'on', try wiggling the key and the wires to the switch, to see if the neutral light stays on.

[lash]

Hate to suggest the obvious but checked the drive chain? I had one with a weird tight spot and when it lined up the sprockets just right it gave the strangest sensation right through the bike (I thought it was clutch related). It would also do it occasionally when setting off from rest!

Showed up when up on the centre stand and I was spinning the rear wheel. After a few revolution it suddenly almost stopped turning and needed extra force to rotate.

Not obvious to me John, but that could just be it, the chain is a little tight. I will try that out tonight!

[grcamna2]

The drive chain sometimes has that issue on bikes when it wears unevenly:a type of oscillation..

[lash]

Well it’s not the chain. But I have figured out that it is fairly smooth to about 3500 and then as I get past 4000 and towards 5000 it starts missing. More noticeable after it has been ridden 20-30 miles and has warmed up. Yesterday was the first really warm +25 or so day I had it out and that made a noticeable difference. I might try a different points plate

[lash]

Sean had a similar problem when he arrived in New Hampshire. He thought it was the clutch too. He pulled it apart and everything was in spec with the clutch. Readjusted and still had the problem. Andy750 sent a message that he had a similar issue in Austria going up a mountain. He found a loose screw on the shifter drum end in the shifter/transmission cover.
I noticed a rattling in the shifter side while I was there shifting the bike at idle on the centerstand (and wondered if something was amiss in the shift linkage)
Sean popped off the tranny cover and sure enough that screw was loose on his. It was allowing the shift linkage to not shift fully into the gears. We cleaned up the threads on the wire wheel, put some blue loctite on and tightened it up. As far as I know that fixed it still.

How would this affect the clutch? Not something I would have thought of..

[willbird]

One of my 69 cb750 is giving me grief and I need opinions. If I hold steady at 4000 rpm as an example the bike lurches like the clutch is slipping, but I replaced  the clutch and basket with a new one and no change. Carbs have been checked, cleaned and synced. Only thing left I can think of is electrical. I am not seeing any sparking at the points, it is timed correctly.
I am not an electrical genius so any suggestions would be greatly appreciated.

Not TOO tough to jumper out the kill switch on a temporary basis to rule it out. I have not studied the 69 schematic but on my K2 one wire goes out to the kill switch and a returning wire from the hand control plugs in to power the coils, a short jumper could easily replace the kill switch for a test ride.

[newday777]

Sean had a similar problem when he arrived in New Hampshire. He thought it was the clutch too. He pulled it apart and everything was in spec with the clutch. Readjusted and still had the problem. Andy750 sent a message that he had a similar issue in Austria going up a mountain. He found a loose screw on the shifter drum end in the shifter/transmission cover.
I noticed a rattling in the shifter side while I was there shifting the bike at idle on the centerstand (and wondered if something was amiss in the shift linkage)
Sean popped off the tranny cover and sure enough that screw was loose on his. It was allowing the shift linkage to not shift fully into the gears. We cleaned up the threads on the wire wheel, put some blue loctite on and tightened it up. As far as I know that fixed it still.

How would this affect the clutch? Not something I would have thought of..

It didn't effect the clutch. Sean was thinking it was the clutch as he had to keep adjusting the clutch, 3 times from Halifax landing, 1500 Km before getting to my place.  It was hard to find neutral, that was why he thought it was the clutch.

[BenelliSEI]

Well it’s not the chain. But I have figured out that it is fairly smooth to about 3500 and then as I get past 4000 and towards 5000 it starts missing. More noticeable after it has been ridden 20-30 miles and has warmed up. Yesterday was the first really warm +25 or so day I had it out and that made a noticeable difference. I might try a different points plate

Did you put new spark plugs in it? New NGK’s have been a disappointment lately. Try a set from a bike that is running great?

While you’re doing that, make sure all the plug caps are solidly screwed into a good piece of wire too……..

[Don R]

 My mind goes to that picture of the sprocket with no teeth left on it. It was a post from a bike shop making the rounds on FB a while back.
 I actually took one of those off of a bike a while back, it had 3 teeth missing, I always wondered how some teeth wore off but not others.

[lash]

They are new NGK’s from my local dealer. What else would you recommend?
Also hooked in a Hondaman unit and that seems to have smoothed it out quite a bit.

[BenelliSEI]

Advancershaft slightly bent?

[HondaMan]

They are new NGK’s from my local dealer. What else would you recommend?
Also hooked in a Hondaman unit and that seems to have smoothed it out quite a bit.

If that's the case, try disconnecting the condensers from the points while the Transistor Ignition is still connected, and ride it that way to test.
I had a CB550 act vaugely like you describe, and it turned out to be a failing condensor. If the bike runs fine with them disconnected and with the Transistor Ignition tied in, try to find some older, used condensors from TEC or Hitachi.

With the 'bad' condensors I have had in my own 750 (back in 2018-ish season) they acted bad when hot, but worked OK when cold.

[spotty]

i get the same sensation on my Vmax, at around 90mph it feels like the clutch is slipping, its actually the back tyre losing grip and spinning like a mad thing, hope this helps

[RAFster122s]

Sounds a little early in rpm and speed range  but a fuel flow problem can cause weird behavior too...

[HondaMan]

i get the same sensation on my Vmax, at around 90mph it feels like the clutch is slipping, its actually the back tyre losing grip and spinning like a mad thing, hope this helps

Believe it or not....once (at my shop) a guy came in with his Yamaha RD400, complaining of 'clutch slip'. He left it with us and I took it out for a ride, discovering that in 1st and 2nd gear, honking on the throttle did indeed let the engine race but without much speed improvement: after I got back to the shop I looked again and discovered threads showing thru his rear tire.

We replaced the tire and that fixed his clutch...we called him "The Happy Yamaha Owner" after that.