Is my clutch slipping?

I should probably know what it's like when a clutch is slipping, but, well, I don't.

When I really lay on the throttle, my tach will run between 6K - 9K really fast, within a second probably, without a big surge in power. The acceleration is good still, but it just seems like I'm losing that part of the powerband, and I wasn't sure if maybe the clutch isn't causing it.

BTW, I'm running pods/jets and 4-1 pipe on an otherwise stock 1980 KZ750-4.

What type/brand of engine oil are you using? Some of the newer car oils have friction modifiers not compatable with the wet plate clutches in thses older bikes.

Shell Rotella is a brand used with success in older bikes with wet clutches.

I'd suggest replacing the oil with Rotella,adjust the clutch and try again.

chrispysaki wrote:

I should probably know what it's like when a clutch is slipping, but, well, I don't.

When I really lay on the throttle, my tach will run between 6K - 9K really fast, within a second probably, without a big surge in power.

That's how a slipping clutch feels. Been there, done that.

MFolks wrote:

What type/brand of engine oil are you using? Some of the newer car oils have friction modifiers not compatable with the wet plate clutches in thses older bikes.

Shell Rotella is a brand used with success in older bikes with wet clutches.

I'd suggest replacing the oil with Rotella,adjust the clutch and try again.

Might want to flush the crankcase with some Seafoam before changing the oil to get the stuff off the plates. Couldn't hurt.

Another trick is to adjust the clutch at the clutch lever to ensure factory suggested play and adjust the push rod by removing the little rectangular cover on the left side of the bike.

Someone who knows the procedure can maybe chime in with the specific details.

I adjusted the clutch where the cable connects to the shift lever and at the push rod according to the manual. The clutch works well under most conditions, it's just when I'm running around 3/4 throttle or more that I can feel the engine really want to take off and the acceleration remains constant - not like it bogs, but it just doesn't match the tach.

I'm using some generic 20w50 car oil with a little bit of 10w30 synthetic that I had on hand. I never realized the oil could make that big of a difference.

So, if it is the clutch, are new plates the solution?

pull it apart and measure plates and springs 1st before ordering new clutch.if the steel plates are flat still you can clean them up by glassbeading,stock replacement style springs and fiber plates work best in most situations in my experiance anyway if you need to replace them

New friction plates, and....if you plan on more mods to extract more power, and/or you just want to never need to mess with it for a LONG time -- slightly heavier or even *noticeably* heavier springs to get that sucker to GRIP and STICK.

Guys on here who do drags or race could point out a supplier or web site with a heavy-duty clutch aftermarket setup.

I'm doing it right now on a Kaw 400cc triple that is doing *exactly* what yours is doing -- I give it gas and the revs shoot up but the bike doesn't -- these 400cc triples pop wheelies normally but the clutch is slipping like yours is. I find that personally disappointing *and* embarrassing.

It is a stain on my reputation to drive such a poorly outfitted machine, hence the heavy duty clutch springs and a new set of really stick friction plates I've just put on. I'm looking after the family's good name, and the next time the 400 comes out of the garage, it's popping wheelies. Or the family name is mud, it's a sacrilege. :blush:

better buy yourself a dumbell to get that left arm in shape! :woohoo:

i use stock seasoned(old worn out ) clutch plates and springs in all my bikes but my big drag bike,in that one i use even lighter springs than stock scuff up the steels or better yet bead blast them not sand blast and measure your fibers to make sure they are still in spec and you should be good to go by the scotch brite 3m pads work wonders on steel clutch plates to get the glaze off of them.

I've had this problem.

For me it was the rod adjustment on the clutch cover. Once the bike was hot, it tightened up a bit and would slip like you say, at the top end.
It wasnt until I adjusted it hot with a bit more movement then spec, that it gripped proper throughout the power band.

Cheers, good luck.

Hmmm, that might be worth a try. Definitely cheaper than buying new plates. If I remember correctly, the bike has been cold whenever I've adjusted the rod on the clutch cover. Thanks!