Clutch Slippage at 6k-8k RPM in 2nd-4th.

This is an odd problem I've been having with my '99 VFR. When I pin the throttle in 2nd through 4th gears (and perhaps in 1st and 5th, but not as noticeable) the bike accelerates as normal right up until it hits around 5-6k RPM, then the engine speed suddenly spikes to around 8K RPM and stays there while the final drive tries to catch up. It seems to me like a pretty obvious case of clutch slippage, but I can't figure out what's causing the problem. The clutch isn't exhibiting any other signs of wear, and the pattern of slippage seems peculiar to me. I already changed the oil and put in motorcycle synthetic formulated for wet clutches, just in case it was bad/slippy oil, but the behavior didn't seem to change at all.

Any idea how to fix this?

 

Same thing happened to my VF1000R. I took apart the clutch and it looked fine but I guess over time the plates just lost grip? I replaced it with a Barnett Clutch kit and all was fine. actually, better than fine!!!

 

How does the clutch lever feel?
Normally the clutch should begin to engage approx midway in lever travel and there should be some 'free play' at end of lever travel.
My clutch was slipping in the powerband, engaging too far from the grip and had lost it's free play. Air was getting into the line, bleeding it was only a temporary fix, problem finally solved with a master cylinder rebuild kit, clutch is solid now. I fixed it asap and I don't think I burned up the plates.
Another useful clue - the fluid was discolored by wear debris from the master cylinder seal.

 

How many miles do you have on the clutch?

 

Did you clean out the return orifice in the master chamber? if it is plugged then the fluid pressure will not release and the the clutch will slip. It is a small port underneath a shiny silver plate in the bottom of the reservoir. There is a picture here:

http://vfrworld.com/forums/mechanics-garage/39219-1984-vf1000f-clutch-problem.html#post365991

 

Good that you mentioned that, the o.p. should start there.

(I ran a fine wire through the return orifice while cleaning up the reservoir on my bike).

 

Thanks guys, I'll look into these things. To answer a few of the questions asked so far...

The clutch lever feels fine, though is adjusted to very little free-play.

I don't know how many miles are on the clutch. The bike has 40,000 miles on it now, and had 38,000 when I bought it last month, and the clutch is one of those maintenance items I haven't really done yet (and would rather not do if there might be a simpler solution)

I'll check out the master cylinder when I have time, possibly tomorrow.

 

order new springs along with the fibre and steel plates. End of story, you have an adjuster on your lever but that just adjusts the amount of throw (how far the lever is from the grip) cables are superiour in that regard. You could have air in the system, but without actually looking at it, cant say. If it loses fluid for any reason, you need to rebuild the massa cylinder (clutch-side) could be a bad slave too. You could take that 10mm bolt off the lever and un-screw the chrome bolt and remove the clutch lever, at that point, you could gently get into where the rubber plunger is and remove it with a bent pick and have a look. If its nasty and calcium looking there, that might be a start.

Anyway, Keep us posted...Cheers

 

How much fore play?

No free play at the lever can be caused by a clogged return orifice in the master.

 

When that orifice for the return is clogged it mimics a real stiff lever. Bike almost is un-rideable...Cure for that is a little creative rheeming with a wire hi-jacked from a grill brush or similar (double secret agent tricks here.)

 

Really? That's good to know. :wink:

My '99 has had a few slips around 6-8K recently too under very hard throttle. I guess at 80K my clutch is about toast, time for a new one. 40K miles seems low to burn through a clutch on the VFR but you never know.

 

More than likely it is your plates and springs. I have a 98 and tried some hp4 synthetic honda oil thinking I would upgrade from the gn4 regular honda oil. On the first 200 mile ride it slipped a couple times when it had never slipped before. I changed my oil back to the regular gn4 and hasn't slipped anymore. My. Bike has aroud 32,000 and I ride fairly hard at times. You could try a regular oil and see if that helps?