Picked up an old J300

[Beaker99]

So I picked up an old Kawasaki J300 on the weekend. It’s a 2013 model with 40,000 km on the clock that’s has been sitting for the past 18 months outside and unused. The owner said he started it once in the past 18 months. I already own a J300 but I managed to have an altercation with a car on the motorway a few months back and although my original bike still runs beautifully, it suffered plenty of cosmetic damage. Trying to find a replacement headlight and fairings etc in New Zealand that don’t cost the earth is near impossible. So I was on the lookout for a donor bike and happened to pick up this 2013 model for NZ$1,200.00.

My plan was to strip the headlight and plastics I need off this bike and use them to get my original bike back on the road and I’ll probably look to do that over the coming month or so. But in the meantime I was keen to see just what shape this old scooter was in. It was very faded and covered in cobwebs etc, but after a good wash it didn’t look too bad. I then put a fresh battery in it and turned it over for a few seconds. It didn’t fire the first time, but on the second attempt it sparked straight up and sat idling nicely. I was pleasantly surprised. So I gave it an oil and filer change and decided to take it on a tentative run around the neighbourhood. It handled horribly. Cornering was a hair-raising experience with the whole thing feeling very unbalanced. After thinking about it a while I realised I never check the tyre pressure. Both the front and back were at 14 psi and not the recommended 29 and 33. With that remedied I rode it again and (not surprisingly) the handling issues were gone. Nice.

It does run a little rough though. In the lower rev range it drives ok, but it seems to lack a little power, especially in the higher rev range. It struggles above 5,500 rpm, where as my original bike is only just starting to get excited above there. I’ll check/adjust the valve clearance’s this weekend and put a new spark plug in. I’m hoping that might solve it. I’ll also get into the transmission and check the belt, clean the housing and maybe deglaze the clutch. Is there anything else I should check on a bike that’s been neglected for a year and a half? Anything in particular that could be causing the lack of top end power?

[CROSSBOLT]

Air filter condition and fuel. What a noble find!

[mousejunks]

It does run a little rough though. In the lower rev range it drives ok, but it seems to lack a little power, especially in the higher rev range. It struggles above 5,500 rpm, where as my original bike is only just starting to get excited above there. I’ll check/adjust the valve clearance’s this weekend and put a new spark plug in. I’m hoping that might solve it. I’ll also get into the transmission and check the belt, clean the housing and maybe deglaze the clutch. Is there anything else I should check on a bike that’s been neglected for a year and a half? Anything in particular that could be causing the lack of top end power?

Definitely use fresh fuel with optional injector cleaner. For some reason the DT300i (which the J300 is based on) runs better on 95 or 98 premium. You can drain the old fuel from the tank using a hand pump and by disconnecting the fuel injector hose (after removing the fuel pump relay and turning on the ignition to depressurise it).

For the transmission, you will have to take apart the front pulley and check that the rollers are rolling and the ramp plate is not stuck. The variator also needs to slide on the axle splines, so add some grease. For the rear pulley, make sure the axle splines and needle bearings inside the clutch assembly are also greased. The belt should be in good condition, so no cracks or bad glazing.

Make sure the gear oil is changed. There are only 2x12mm plugs (don't over torque) and it uses 190mL of SAE90 or 80W-90 gear oil.

The last thing to check are the brakes. If the pads are lalready in good condition and have plenty of material, take apart the calipers and grease the sliding pins to avoid rust. Also clean the shims with a wire brush and brake cleaner and finish off with caliper grease.

[Beaker99]

Thanks for the replies. I'll get into it this weekend and report back on the results. It definitely feels like with a bit of work this bike could have a lot more life in it.

[Kansas kymco]

I would also flush the brake fluid if it's sat outside for  a extended period of time.

[Beaker99]

Well I couldn't wait to get into the old J300 and so spent a few hours on it last night. I put a new spark plug in (the old one didn't look too bad), adjusted the valve clearance (a couple of them felt a little too wide/loose), and put a new air filter in (the old one was a mess and looked like it hadn't been changed in a very long time). I then got into the transmission and pulled out the variator which was in need of a good clean. There was plenty of belt dust build up in there. The belt itself looks ok, it measures 24mm wide, so I put it back on for now.

I then took the bike for a spin around the neighbourhood and the difference is like night and day. It preforms just as it should. It rev's freely right throughout the rev range easily getting up to 6,500rpm if I open the throttle. The ride is so much smoother as well. I couldn't be happier with it. It's hard to know if the improvement is from any one of the actions taken, or if it's a combination of everything, but I strongly suspect the engine was struggling to breathe through that old air filter and that may well have been why it was struggling when I opened the throttle previously.

I still have a lot to do. I will flush the old gas and fill it with 98 tonight. I'll then use this weekend to get into the braking system. Will pull the callipers apart and grease / service them and change the brake fluid. I might as well give it a coolant flush as well. With that done the next job will be to get into the cosmetic side of things. There’s no physical damage to it at all but I want to try and revive some of the faded black plastic to get it looking as good as it now performs.

[mousejunks]

Wow good work with the J300.

For faded black plastics I use Autoglym bumper and trim gel. Lasts a long time and isn't too glossy either giving it a natural plastic look

[Beaker99]

I had a crack at servicing the front brakes on this scooter on the weekend. They have been dragging badly, to the point that the front wheel only rotates (when it’s off the ground) if I’m physically moving it. When I try to spin it, it stops the second I take my hands off it. On my other bike the front wheel will rotate nearly a whole rotation if I spin it and take my hands off.

The pads were so tight against the rotor I couldn’t lift the caliper off. I had to tap it with a hammer to wiggle it free. After removing the pads I watched the pistons as I pulled the break leaver and one seemed to move freely, while the other barely moved at all. I used a c-clamp to hold the first one in place and pumped the leaver again and this time the stuck one moved out. There was a little bit of marking / corrosion on the pistons, but to be honest it didn’t look like much. I gave them a good clean and a rub (at least as much of them as I had exposed) with a scotch pad and after cleaning the whole caliper then greasing the pistons and pins etc with copper grease I put the whole thing back on the bike, fully expecting my brake dragging issues to be solved. I was wrong. It’s exactly the same.

So my next thoughts are:

1)   Bleed the system to make sure there are no air bubble. Could that cause the breaks to bind/grab like this?
2)   Completely disassemble the caliper and remove the pistons to give them a much better clean and replace all the seals. I’ve never done it before, but it doesn’t seem to complex.

I haven't flushed the brake fluid yet, but will end up doing that if I take whole thing apart anyway.

Are there any other options or things I could try before taking it all apart?

[mousejunks]

So my next thoughts are:

1)   Bleed the system to make sure there are no air bubble. Could that cause the breaks to bind/grab like this?
2)   Completely disassemble the caliper and remove the pistons to give them a much better clean and replace all the seals. I’ve never done it before, but it doesn’t seem to complex.

I haven't flushed the brake fluid yet, but will end up doing that if I take whole thing apart anyway.

Are there any other options or things I could try before taking it all apart?

I would do option #2 or replace the entire caliper, the brakes shouldn't seize because of air. Air would cause spongy braking.

[Iahawk]

sounds like you'll need to pull the caliper apart, again, and replace seals, etc. while also looking for any additional corrosion of the pistons. Not sure if your caliper has slide pins but if you do you want to make sure they are also clean, lubed and moving freely.

What is the condition of the brake fluid? You'll want to replace it. Let us know how it turns out.

[Beaker99]

Just a bit of an update. I purchased new rubber, front and rear, for the J300 and set about fitting the tires myself. The front was no problem, once I figured out the best method of breaking the bead. The rear however is a different story. It was all going smoothly until I tried to remove the subframe that slides on over the right side of the axel. I saw a few mentions of it being difficult on some older threads here, and they we're not wrong. It's not coming off, no way, nada, no hope in hell. I tried everything eventually resorting to a propane torch with the hope of enough heat expanding the metal and breaking whatever bond is holding it in place. Still no joy. I had to admit defeat and put the bike back together with the old try still in place.

Today I rang a bike tire shop to see if they would do it and had an interesting conversation with the owner. He was quizzing me about weather the tire has ever been replaced before, obviously trying to preempt this exact issue. When I told him about my struggles he said I had to take it to the local Kawasaki dealer as this was a problem on many of these early models. Mines a 2015. Apparently he's run into this issue a number of times and had to refer the bike to the dealer who has to apply so much heat to get the subframe off, that it destroys the bearings. It sounds like Kawasaki was covering the cost of the removal and bearings a few years ago, but I'm yet to confirm that. I suspect however I'll struggle to get anyone to cover the cost at this point in time. Got the scooter booked in for next week, so hopefully the dealer has better luck than me.