Motorcycle Clutch or Transmission Slipping?

The first thing to do is get a factory manual and make sure all the adjustments are at factory spec. That goes for throttle cables, clutch adjustments, chain tension, and anything else that you can think of. Make sure you also do an oil change, and then after a few hundred miles do another. An abused bike can take an entire friction disk and dissolve it into your oil in one afternoon. That can eat bearings faster than you would believe. Once you get all the external adjustments and specs ironed out, if it doesn't fix things, then you need to open up the clutch cover and check to see that everything in there is within specs too. Don't dismiss the idea that your slipper mechanism is worn. Everything needs to be checked until you isolate the problem.

I agree with the last responder, check the drive chain. Check the slack while you're setting on the bike. Also check to see if the chain is worn out. At the back of the rear sprocket, grasp a link between your thumb and forefinger and pull back (away from the sprocket). If you can see more than half of the tooth's height, the chain is shot. A worn out chain rides high on the teeth, resulting in 25-30% of the teeth on the sprocket handling all of the load compared to about 60% otherwise. When you accelerate, the teeth in the 1-2 o'clock position handle the load, when you decelerate, it's the teeth at 4-5 o'clock that are loaded, resulting in a lot of slack during the transition.

Some bikes have more slack in the drive train than do others. My old 750 Honda had PLENTY compared to my two Kawasakis. Normally most of the slack is in the bottom two gears. If your bike is fuel injected, FI systems can be rather abrupt at time, accentuating the slack problem. It certainly is on my 6 cylinder Kawasaki.

How are you checking the chain tension? The chain is much more slack under load than when the bike is standing still.

I had a similar issue and couldn't locate the noise for months.

Then one day I was riding at sunset and I was watching my shadow and I saw the chain clanking against the swing arm. It was much more slack in motion than when I toe tapped it with the bike on the stand.

In my case the chain was just worn but try tightening the chain. Make sure you're not missing any teeth in your sprockets.

Fuel injection isn't supposed to thump like that.

I think this is the fuel injection setup – it was engineered into the ECU which delivers what it believes is safe and then what the rider wants. The solution is either to live with it or to use a different ECU. The newer cross-plane crank R1 has had it engineered out in some of the power modes.

Pull your clutch cover and check the basket for excessive wear if this is ok you'll need a new primary drive chain.There is a better chance that the clutch basket is worn out than the chain.

That's the slipper clutch you feel disengaging and engaging. It is designed that way the prevent rear wheel lockup.

Sounds like it is working perfectly well and there is nothing wrong with your bike.

I'd inspect the primary drive.

I'm not sure what those Jap things have but I'd guess some kind of gear between the crank and clutch basket.

That's a really interesting question, looking forward to going through the responses