Jet Ski Circles

[redpoint5]

For some reason I let my 1990 Kawasaki 550 stand up jet ski sit unused for the past 6 years. Well, this week I finally dipped her into the local lake and became a jet skier again. It went better than I had anticipated, with the ski running strong, and my skill about where I had left off (not very skilled). It's like riding a bicycle!

Normally when I fall off, it's from doing tight circles and falling over. When this happens, I'm going slow enough that I can hang onto the grip and pull myself back onto the ski. Occasionally, I'll wipe out when going faster due to a wave catching me off balance, or a botched fast turn. Falling off at speed rips the ski from my grasp against all determination to prevent it. At that moment, its supposed to return to idle and make tight counter-clockwise turns.

I fell off while doing one of those faster turns, and this time, to my horror, the ski fast-idled away from me. It went in the general direction of some kayakers, and I figured at best, the ski would end up on the rocks, or at worst, into the people.

Eventually the ski decided to end its terror run and instead turn circles like a normal ski. Swimming the 200 yards or so in 10 minutes with a bulky life jacket made me realize 2 things:

1. I'm out of shape
2. I've got to do something to prevent a runaway ski

I think the idle is set a touch too fast, which may have prevented the ski from circling. I'm not sure what causes the ski to circle in the first place, because the steering doesn't have a spring or anything to cause it to turn.

I'll probably just install a lanyard kill switch. It means I'll have to swim further to get to the ski when I fall off, but it's much better than watching it ride off into the sunset.

Funny that I never even contemplated the unthinkable of happening until it nearly did.

[ChillyBear]

Sounds like its running lean. "Running strong" is often a bad thing on a two stroke lol. They run best right before the pistons seize....and they idle high. Case leaks/bad reeds can do that too.

If it's been parked for a while, that could be a very real possibility. If you have dual fuel pumps, I'd make sure the pulse port is clear, and that the first pump is clean, or that the pilots aren't clogged.

Jetski's are detuned, but It risky to fire up a two stroke right out of storage and go hard on it IMHO.

[jamesqf]

Originally Posted by redpoint5

1. I'm out of shape
2. I've got to do something to prevent a runaway ski

Perhaps I'm belaboring the obvious here, but you could remedy both problems by just trading it for a kayak :-)

[redpoint5]

Originally Posted by ChillyBear

Sounds like its running lean. "Running strong" is often a bad thing on a two stroke lol. They run best right before the pistons seize....and they idle high. Case leaks/bad reeds can do that too.

If it's been parked for a while, that could be a very real possibility. If you have dual fuel pumps, I'd make sure the pulse port is clear, and that the first pump is clean, or that the pilots aren't clogged.

Jetski's are detuned, but It risky to fire up a two stroke right out of storage and go hard on it IMHO.

I was thinking more about this comment, and it doesn't seem like it could idle faster by running lean. How does less fuel result in higher idle and more power?

I'd think my problem is simply the idle setting, or the throttle return spring not closing the throttle entirely.

Originally Posted by jamesqf

Perhaps I'm belaboring the obvious here, but you could remedy both problems by just trading it for a kayak :-)

I have 2 creek boats and an inflatable kayak. I'm considering buying another jet ski since my trailer holds 2, although I might just transport one of my creek boats on it to the lake. It would be annoying to go any distance since it turns too easily and doesn't track, but that's what I've got.

[ChillyBear]

I'm not like an expert lol, but in general when I tune a two stroke by ear after say cleaning the carb etc, I would always adjust to peak rpm on an adjustable high jet if its a small carb, or just a richer jet if its a big carb on a not stock motor, and then richen until the rpm dropped a tad. Two strokes have a tendency for the exhaust temp to creep up under load. However, I think the main thing is flame speed as far as the rpm/power gain. Two strokes always run "extra" good right before they burn pistons. Or what moto-x/go kart guys call the "lean edge" something you find if you have the budget to rebuild motors every 3 hours, with custom micro polished clearances etc, it's so wasteful.

But I thought of my comment later, and realized that you probably have oil injection. I've never blown a jetski up. But I have death with jetski keinhin dual fuel pumps on my old go kart. It ran on methanol, so I got to experience a new fuel system clog every 3 days of sitting lol. But it had floatless carbs, holy crap what a nightmare to get the fuel pressure right.

Lean runaway will happen on two strokes at high rpm if they have vacuum leaks or carbon build up, or are being starved of fuel. OMG not fun. You can pull the plug wires and it will still diesel or whatever the hell it's doing, and will do some crazy stuff. Depending on the engine bore/stroke and the fuel, knock/ping can feel like a second/third power band, or it can just be a fast burning lean mix.

But vacuum leaks can cause that high idle, and will also (obviously) make it run lean. red rtv is your friend on a two stroke, my exhausts always have red +2000°f red rtv on them two. Its a nice feeling to KNOW your performance is from proper tuning and not from running lean. But cases, carbs, reed boxes, everything is COVERED in rtv.

I may also just trying to read between the lines, and took the "running good" and went off on a stoner tangent lol

[redpoint5]

I mix 2-stroke oil with the fuel at 40:1. I'm not sure if the ski came stock with an oiler, or if it always required mixed oil / fuel.

What surprises me is that the ski only makes 41 hp using a 550cc 2-stroke motor. My CBR F4i 600cc 4-stroke delivers 110 hp.

It seems the ski could either have a smaller engine with similar power output, or simply make more power with the existing engine size. Perhaps the ski could even have a 4-stroke with similar size, weight, and power output.

As an aside, the lead-acid battery had dried out and died from sitting so long. I used my 20 Ah LiFePO4 battery to start it. Hopefully I don't hurt them considering the brief 200 Amp initial cranking draw. It's rated to output that for less than 10 seconds without harm. The battery fits the tray perfectly in 1 direction, and is a little skinny in the other direction, and is much lighter. So far it's working out nicely.