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SOLVED - It was indeed due to a missing washer / shim. The inner one that goes up against the crankcase was missing. That allowed the variator to slide back a couple of millimeters, which was enough for it to loose some of it's bite onto the crankshaft. With the variator now free spinning on the shaft, all the driving force was transferred to the outer pully plate, and the soft alloy is obviously not designed to take that much force, so it then shreds the teeth that lock into the grooves of the crankshaft.

I assume the Downtown models have onother drain plug like the other models and you always use the other plug to drain the oil during oil changes.

I never found any dirt stuck at my scooters' screen filters and I've never seen any comments from anyone who ever found any dirt at those filters.

I can confirm this. I used to pull that screen and clean it during oil changes but I never found anything on it. I gave up pulling it out. I've done over 80k km and I reckon the last time I checked it was before 50k. I gurantee if I pull it next time it will be spotless. It's also a pretty long screen, so even if you had some chunks on it, it's hard to imagine it would be enough to slow the flow of oil. If it got to that state you would have much bigger problems. I wouldn't panic. If you are doing regular oil changes you're probably good.

For the crankshaft thread, mostly not demaged by a loose variator plate or nut for those are way softer material.
This a security feature too, to safe the crankshaft as much as possible in case.

Just by way of an update. I finally got around to having a go at "repairing" the messed up crankshaft on the engine I swapped out of my J300. It was surprisingly easy to remove the soft alloy from between the splines of the crankshaft and it looks like it's still in decent condition. So it seems their design security feature worked well and I still have a spare usable engine. Although, given it's got 80,000+km on the clock I'm not sure how much life is left in it. As I have the engine sitting on my workbench, I'm toying with the idea of rebuilding it to give it another lease on life. That might be a project for winter which us just around the corner.

I recently low-sided the bike on a particularly slippery corner on my way to work. Apart from some bumps and bruises I was fine, but the bike didn’t like being dropped very much. I ended up having to replace the steering stem bearings to get the handling back to normal. Aside from that there was the usual cosmetic damage. I needed a new windscreen, and the exhaust shroud was all messed up.

Instead of replacing that annoying plastic exhaust shroud, I decided to try a cheap aftermarket exhaust on the bike. I ended up ordering the below from Aliexpress for around NZD $60.00.

https://www.aliexpress.com/item/1005006863899177.html?spm=a2g0o.detail.pcDetailTopMoreOtherSeller.1.51b4CKPNCKPN3W&gps-id=pcDetailTopMoreOtherSeller&scm=1007.40050.354490.0&scm_id=1007.40050.354490.0&scm-url=1007.40050.354490.0&pvid=18d1b2f5-0d1e-48ea-8d80-d185a3dcce03&_t=gps-id:pcDetailTopMoreOtherSeller,scm-url:1007.40050.354490.0,pvid:18d1b2f5-0d1e-48ea-8d80-d185a3dcce03,tpp_buckets:668%232846%238108%231977&pdp_npi=4%40dis%21NZD%21129.80%2164.90%21%21%21559.50%21279.75%21%40210318ec17270487012103333e5a8c%2112000041506297833%21rec%21NZ%214271177227%21X&utparam-url=scene%3ApcDetailTopMoreOtherSeller%7Cquery_from%3A

It was extremely easy to fit and I was happy with the look of it. It’s also significantly lighter than the stock exhaust. At a guess the aftermarket one weighs about 0.5kg while the stock exhaust must weigh close to 3.5kg. Unfortunately, it quickly became apparent that the new aftermarket exhaust wasn’t going to be usable in its initial form. It was simply way too loud for a scooter. It comes with a “db killer” installed in the rear, but even with that in the noise is obnoxious. I didn’t dare run the thing without the db killer installed. The second issue was that with a much more free flowing exhaust system, the bike was now running on the wrong side of lean. This was most noticeable diving in traffic at 55-60kph when you are barely on the gas, in 1%-5% throttle area. The bike was a little boggoy and simply not happy there. It was fine when giving it more throttle, but as I spend a lot of my time commuting in traffic only barely on the throttle, it wasn’t going to work for me.

So I did some research and came up with a couple of additions to hopefully help the noise and the running lean issue. I ordered a couple of extra silencers to try out, both of which slot into the front of the exhaust. These made a massive difference to the sound, dramatically reducing it to where I was happy riding it in public again. They also helped create a bit more back pressure in the exhaust and the “low throttle” bogging was a lot better. But the other thing I purchased was this little unit from Malossi.

https://www.malossistore.com/en/nz/tc-unit-o2-controller-lambda-emulator-kawasaki-j-300-ie-4t-lc-euro-3-ws60-5516341b-kaj300-M-P

From what I could find online, it seems this ticks the ECU into dumping more fuel in the system by adjusting the values the O2 sensor sends back the ECU. It took 6 weeks to arrive, but I finally received it last week and went about installing it. My first impressions are positive. It does feel like the bike has a bit more power. I didn’t set out trying to improve performance, I just wanted a better looking and sounding exhaust. But it’s a definite positive to have the bike feel like it’s got a bit more pull. The bike is now smooth throughout the rev range and when I do open it up it’s a little more fun than it was before.

There are a couple of other things I’ve noticed since installing the Lambda Emulator. Firstly, the bike takes a bit longer to get up to operating temperature now. I’ve done 80,000 km on this machine commuting to and from work. I know exactly the point in the early part of my journey each morning that the second bar on the temperature gauge lights up. Initially I thought I might have a temperature sensor problem as the bike hadn’t warmed up in the normal time, but about half a kilometer further down the road from normal the bike eventually reached normal operating temperature. It’s consistently now taking this longer time to warm up, and this is even as the outside temp is warmer now than in mid winter. So I can only guess that running richer is making the bike run a bit cooler?

Secondly, there seems to be less “engine braking” resistance when off the gas and “free wheeling” so to speak. I really wasn’t expecting that, but it’s been noticeable from the first ride with the Lambda Emulator. My bike did seem to have a fair amount of “engine braking” before. I’ve ridden identical machines which definitely coasted along off the gas much easier than mine, but I’ve now seen an improvement in that area which is a nice bonus.

Overall, I’m pretty happy with the current set up. I’m enjoying the daily commute on the bike as much as I ever have, and that alone is worth the cost. This bike has been my daily driver for the past 5 years and hopefully I’ll get a couple more out of it yet.

I ride all year round to and from work. I do about 400km per week. This past year has been a pain as it rained all summer, and I’m talking torrential flood-inducing rain. Now in winter there's more rain and it's a lot colder. I’ve got the Scott Ergonomic Pro DP Rain Jacket and pants and they work pretty well, except for one small issue. Water seems to seep through the pants in the crotch area, so I will arrive mostly dry, but looking like I’ve pissed myself!

I’m guessing water pools on my seat and eventually makes its way through the material or seams of the pants. I’ve thought about getting better rain pants but this set rolls up nice and small when not in use and so it doesn’t take up much under seat storage. I’m thinking I’ll buy a can of waterproofing spray for material and spay the inside of the pants so I don’t keep looking like I’ve got an incontinence problem.

A bit of an update. After swapping over the ECU’s I then proceeded to ride the “faulty” bike for 4 days straight, commuting to work and doing all my normal riding. I consistently checked it after each ride by trying to start it back up after 5, 10, or 15mins and the bike never failed. I definitely would have had it fail to start previously within those 4 days if the problem was still present.

I then started riding my usual “good” bike which now had the “bad” ECU in it, and I was fully expecting to have that fail to start at some stage, but it seems it too is running perfectly and I can’t it to fail to start either!

At this point my working assumption is that the issue was ECU related but I fixed it when I performed the reset of the throttle sensor position and idle speed control valve. Aside from swapping the ECU’s between bikes, that’s the only other thing I did on both machines. I’m still riding the “good” bike and I haven’t tested it as much as I would like, but so far it doesn’t seem to have inherited the problem.

Finger crossed I've had a lucky solution. I can now put one of the bikes on the market, which will please my wife immensely!

Hi all,

I have a Kawasaki J300 I picked up about a year or so ago which had been left sitting for 18months before I got it. I did a full service etc and got it running well but it’s got an intermittent issue where it will fails to restart sometimes if it’s been running and warmed up to operating temperature then turned off for a few mins. I happens most often if I ride it down to the shops to pick something up. On a cold start it fires up almost immediately every time. But if I drive to the shop, park up for a few mins and then return, it will often simply turn over and not even try to fire up. It’s like there is no spark. It’s turning over normally but there’s not even a hint of ignition. I usually have to turn the key off, wait 20 seconds then try again and if I do that a couple of times it suddenly fires up as normal.

Does that sound ECU related? Could it be something else?

I do have a second J300 so I’m thinking about swapping the ECU’s over to see if that fixes the problem, but I’m really dreading having to strip down two bikes to get to the ECU’s.  Is there anything else I should look at / test before blaming the ECU?

"I also recommend cleaning/washing the CVT intake filter more often than 5000km otherwise it can overheat due to dust clogging. It's low to the ground so it gets dirtier than it should."

I can concur with that! I'm always suprised how dirty that little filter is when I open the transmission up.

I ride 300km-500km per week on my 300 and I change the oil every 3,500-4,000 km or so. It works out to around once every couple of months. I don't live in hot dusty condtions which I can only imagine would be a bit more harsh on the scooter, but I'd be surprised if it would really make much difference whether you change at 2,500 or 3,500. It's still well earlier than the recommended interval and should keep the scooter running well. It's a quick job and there's not that much oil involved in a change so it does't cost too much. Between the oil and filter it probably cost me $30 per change.