Clutch Slipping, or Oil to blame? (79 KZ650SR)

Is this what your carb rack looks like? If they are correct then the spring loaded gizmo is the accelerator pump

I’m curious to what your “clutch slipping” feels like? (I also have a ‘79 SR)

I just got a new clutch cable and it’s all adjusted to spec so that’s not a worry, but I did change my oil yesterday with the Kawasaki brand 4-stroke 10w-40 oil and my rpms dropped by about 250 across the board. Went from 5200rpm at indicated 60mph to a hair under 5000rpm at indicated 60mph...

I saw a comment on this thread about drag racers wearing out clutch plates and I wonder if at one point my bike was a drag bike....had an NHRA sticker on the back, previous owner said he had to do the piston rings from low compression, had straight pipes, and it seems that the clutch doesn’t have as much “grab” as it should. Who knows haha.

My two questions are: Will worn fiber plates leave any telltale signs in oil when you change it? and would going from a 20w-40 or even car 10w-40 oil with all the additives to the 10w-40 motorcycle specific oil be the cause in the 250rpm drop I experienced? (I don’t know what oil was in there when I bought it)

Not so good. Assuming stock sprocket and counter sprocket the KZ650 should be running right around 4500 rpm at 60 mph. Ed

Ed - I saw that on another thread, have yet to count the sprocket teeth, will do so when the new chain comes in. Hoping that’s the issue other wise I have some problems

Mikaw wrote: Is this what your carb rack looks like? If they are correct then the spring loaded gizmo is the accelerator pump

OK, that makes sense. Accelerator pump. I might fool around with it later today, but the weather is supposed to be beautiful, so after work I may take another bike out for a ride to clear my head. This one can sit until over the weekend.

Sorry for the delayed response - the forum never notified me of new replies. I decided this morning to check on it.

-John

2WheelJunky wrote: I’m curious to what your “clutch slipping” feels like? (I also have a ‘79 SR)

I just got a new clutch cable and it’s all adjusted to spec so that’s not a worry, but I did change my oil yesterday with the Kawasaki brand 4-stroke 10w-40 oil and my rpms dropped by about 250 across the board. Went from 5200rpm at indicated 60mph to a hair under 5000rpm at indicated 60mph...

I saw a comment on this thread about drag racers wearing out clutch plates and I wonder if at one point my bike was a drag bike....had an NHRA sticker on the back, previous owner said he had to do the piston rings from low compression, had straight pipes, and it seems that the clutch doesn’t have as much “grab” as it should. Who knows haha.

My two questions are: Will worn fiber plates leave any telltale signs in oil when you change it? and would going from a 20w-40 or even car 10w-40 oil with all the additives to the 10w-40 motorcycle specific oil be the cause in the 250rpm drop I experienced? (I don’t know what oil was in there when I bought it)

My clutch slipping feels like any manual car I've ever driven - you give it throttle and the engine RPMs increase but your speed doesn't.

What doesn't make sense to me in your situation is having lower RPMs at a set speed, unless your clutch is always slipping some? RPMs for a certain speed is pure math, and the clutch shouldn't have anything to do with it, unless the clutch is ALWAYS slipping on your bike.

-John

SR's are geared differently than B & C models, they also have a 16" tire
Stock sprocket combo is 16/40
The accuracy of 40 some year old mechanical gauges are questionable at best
a couple hundred difference in RPM's is not something I'd worry about.
A slipping clutch should be noticeable by engine RPM not matching a increase in bike speed

Yeah the clutch isn’t slipping then...

Still haven’t counted my teeth and all but I think I may chalk it up to the gauge reading about 500rpm high as its running pretty healthy but always prefers to idle at closer to 1500rpm indicated rather than 1000rpm. So same rpm difference between expected and real values.

Either that or my motor is messed up :woohoo:

There's an idle screw on the carbs (it's a thumb screw), which I don't have a picture of, but if you turn it left and ride, it'll change the idle speed. You can easily use it to lower your idle RPMs. Mine is adjusted so the bike will start and idle, but once fully warmed up, it idles closer to 2,300 RPMs. If I lower the idle once the bike is fully warm, it won't start.

As to my carb issue, I decided to tinker with it today, and went out and tapped the #2 float bowl a few times with a screwdriver handle, and then fired the bike up. It started right up, went off choke, warmed up fine... and no leaks! Took it to do a wellness check on my mom (she's fine, thanks for asking LOL) and 15 miles round trip saw no issues. Bike's clutch engaged perfectly, bike took off from stops better, no leaks. The only issue was the wind - 20-25mph gusts added a little rear end wiggle at times, but I had fun.

-John

drakhen99 wrote: There's an idle screw on the carbs (it's a thumb screw), which I don't have a picture of, but if you turn it left and ride, it'll change the idle speed. You can easily use it to lower your idle RPMs. Mine is adjusted so the bike will start and idle, but once fully warmed up, it idles closer to 2,300 RPMs. If I lower the idle once the bike is fully warm, it won't start.


-John

You still have a problem. Probably clogged pilot circuits, or possibly a problem with the enricheners. You should start a new thread in the carburetor section.

Yeah, I figured it still has issues. My indy shop said to call them later this week to schedule a time to drop the bike off for a carb rebuild. Not leaking means I can just ride it in instead of trailering it.

I don't mind paying for good work to be done when I don't have the space or time. I did the bobber conversion in my glassed-in porch for my Vulcan 800, and have done little projects here and there, but I'll gladly pay for it to be done right. Honestly, the bike hasn't cost me anything over the last couple of years, so my "KZ repair fund" is flush at the moment.

When my boys are older, if they show interest and I have a garage at that point, I'll start diving into stuff like this, but at the moment, time and space are very limited. If I get a couple of hours to spend with my bikes, I'd rather be riding them than working on them, you know?

It would be different if I had a local friend who would be willing to drink some beers and help me out with this stuff, but me fumbling through it is only going to lead to curse words and family strife.

All that said, I really appreciate everyone's help on this forum, as I'm learning more and more (ie, the clutch cable adjustments) and building my skills and confidence. If there's a quick or easy fix I can do myself, I'm all for it. (carb rebuild is neither quick nor easy, at least to me)

-John

I understand. We are all limited to 24 hours per day. Sometimes it makes sense to pay an expert. Sadly, there are fewer and fewer KZ experts in business, so you are fortunate to have one nearby.