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Help: Setting cruise speed on Sportster LE

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tawood

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Hi all,
I'm new to the forum, and I'm hoping someone can answer a question for me.
I have a 2001 Sea Doo Sportster LE (single 130hp Rotax 947), that I bought last summer. The boat starts great, has good compression, and doesn't seem to miss a beat except for one thing: it doesn't want to run at a constant speed.
I have 2 small kids that like to tube, but at relatively low speed (GPS measured speed of about 18 mph). I used to pull them on my Yamaha SUV and it was no problem to dial in the speed, but my Sportster is giving me fits.
If I set the throttle so the boat will run at 18 mph, it will do so for about 15-30 seconds, then it will slowly accelerate to about 30+ mph if I let it. If I reduce the throttle even just a touch, it will slowly decelerate to about 8 mph. I have checked the throttle cable and it is not moving during these times. Engine RPM does change however during these times.
I'm an aircraft mechanic, so I am knowledgeable about engines...I'm thinking it could be a normal (boat getting on plane, or maybe power valves (if it has them) opening up) or not (lean surge? something else?).
Anyone else experience this? Is it normal?
Thanks in advance,
Tim
 
Tim I'll be back at 8:00PM with an answer for you ... I see you haven't got an answer since yesterday at 2:50 pm...
Karl
 
Ok Tim, When you not pulling the tube how is it running? Are the RPM's all clean and crisp? Does it rev up on it's own at high speed and not go any faster?

Karl
 
Tube or not

It runs great, no misses or hesitation but.....tube or not, it does run up on it's own, and of course, it runs up even faster if there is no tube.
If I immediately go to hi speed (such as give it full throttle), it accelerates just fine and tops out about 50 mph (50 GPS, speedo says 60!!!). It will slow down slightly in corners, but maintains constant speed in a straight line no problem at full throttle.
 
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It sound like you might have a planning problem. the rpm's shouldn't change unless it is bogged down from the weight till it runs on plane level in the water. Than it will pick up speed cause it is riding on top of the water and not plowing it.

ScubaDoo
 
ScubaDoo has some good insight, but lets go back for a minute...you said it has good compression. What is the compression of the engine. It is preferred to have 150psi per cylinder. If is is low it could be the problem as the engine needs high compression to have the torque to pull any weight. Do a Compression test, This will tell us a lot about the internals of the engine. If nothing else we won't be guessing it's bad. Do you know the proper way to check the compression? If not let us know and we'll give you the heads up.

Karl
 
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I think so...

I'm assuming no gas supply, carbs wide open, just like any other engine, right?

I'll try to recheck it this weekend.
 
Kinda...Use a compression guage that screws into the plug holes, not the push and hold type. Pull the spark plugs...put the caps on the studs next to the cylinder head, to ground them and prevent further electrical problems. Don't worry about the fuel line. Carbs Wide open, Crank it till it reaches peak. Idealy it should be at 150psi per cylinder. Let us know how you make out.

Karl
 
Kustom Karl: Compression test done

Sorry about the delay....cylinders were 150 each, right on the nose.
 
That's a good thing...that engine should last a long time. Now what problem are you still having...any updates?

Karl
 
tawood said:
Hi all,
I'm new to the forum, and I'm hoping someone can answer a question for me.
I have a 2001 Sea Doo Sportster LE (single 130hp Rotax 947), that I bought last summer. The boat starts great, has good compression, and doesn't seem to miss a beat except for one thing: it doesn't want to run at a constant speed.
I have 2 small kids that like to tube, but at relatively low speed (GPS measured speed of about 18 mph). I used to pull them on my Yamaha SUV and it was no problem to dial in the speed, but my Sportster is giving me fits.
If I set the throttle so the boat will run at 18 mph, it will do so for about 15-30 seconds, then it will slowly accelerate to about 30+ mph if I let it. If I reduce the throttle even just a touch, it will slowly decelerate to about 8 mph. I have checked the throttle cable and it is not moving during these times. Engine RPM does change however during these times.
I'm an aircraft mechanic, so I am knowledgeable about engines...I'm thinking it could be a normal (boat getting on plane, or maybe power valves (if it has them) opening up) or not (lean surge? something else?).
Anyone else experience this? Is it normal?
Thanks in advance,
Tim
Click to expand...

Tim, I would Clean the RAVE,(Rotax Adjustable Variable Exhaust) valves.
The RAVE, (Rotax Adjustable Variable Exhaust) valves are located above the exhaust valve. There are 2 of them per engine. They are round with a red adjustment screw in the middle. It has a clip that holds it together. How they work is that they open the exhaust port larger as the engine rpm's increase. When the rpm's drop down so do the RAVE valves. They work on the principle of the pressure of the exhaust system.The 947 engine uses a solenoid operated by the MPEM,that can't be serviced. Rpm's increase, pressure increases and the valve opens, rpm's drop pressure drops, Valve closes. They should be de-carbonized annual. To disassemble the rave valves, remove the spring clip on top, remove the black cover. There is a spring under the cover. Remove the piston by turning it with a metric socket. On the bottom of the piston is the rubber "Bellows" be careful with the small retaining spring that hold the bellows on the piston. Remove the 2 allen screws that hold the base on the cylinder. Remove the base and gasket. The long valve won't fall in the cylinder just pull it out. There is an o ring under the base, on the shaft of the guillotine valve. Be careful to see how it came apart as it has to go back together that same way again. On the base, notice the notch that it is facing down. Clean all the carbon off the guillotine valve. I use carb cleaner and 400 grit paper. Check the bellows for any small pin holes. If so replace it. If not, reassemble it on the clean guillotine valve, and install it back on the engine the same way it came apart. The guillotine valve only fits one way. The one closest to the exhaust pipe will come off differently then the other one. You will have to remove the allen screws and turn the base so it clears the exhaust pipe. I would do one at a time in case you forget how it goes back together again. This way you can look at the other one and copy it. Do both engines 2 per engine. Take your time and if you have questions give us a shout. We'll be here to help you out.
If the RAVE valves are dirty it will not rev up correctly and could be causing your problem.

Karl
 
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Thanks Karl

I'll start it tonight, then let you know how it went when I'm done....I have the boat in the garage now, so I'm ready to get started.
Thanks again,
Tim
 
Straight forward job, but....

Cleaning the RAVE system was very easy, and took me only about 45 minutes. I do have one concern though...
I've been racing 2 stroke motorcycles for years, and I've cleaned many a dirty/carboned power valve. My concern is: these valves were just cleaned! There was NO carbon what so ever, and only a light coating of (burnt) 2 stroke oil that wiped right off. The valves, in my opinion, were original though (wear marks, etc).
Now, I bought this boat from the original owner mid-last summer, and I've only put about 3 or 4 hours on it since then. The original owner took good care of the boat, but to clean the power valves, right before selling the boat??? That doesn't really make sense, unless he was trying to fix the same problem that I am.:confused:
 
It sounds like you might be on to something...I have seen the RAVE valves full of carbon in just a few months of use. The Water Regulator flow valve on the exhaust resonator could be interfering the RPM's too. Try the pwc and see how it runs now. I like to check the operation after one change rather than doing multiple's so we know what did the repair. If it is still the same, here is something else to check. The Water Flow Regulator valve, looks like a RAVE valve, it sits on the resonator of the exhaust.

Water Flow Regulator Valve;

The water flow regulator has been calibrated at the factory and should not be tampered with or modified in any way.
CAUTION: Strictly adhere to the calibration procedure or otherwise serious engine damage will occur.
If engine does not maintain RPM or the engine is experiencing poor performance, the water flow regulator valve might be out of adjustment. The normal adjustment as done at the factory is as follows: On the top of the water flow regulator valve locate the red plastic adjustment screw. Mark the location of the screw with a dab of paint for reference. Turn the screw clockwise (tighten) until the top edge of the screw is flush with the top of the black cap. Turn the screw 2 clicks counterclockwise (loosen). This is the factory spring setting. The bottom tapered screw should be screwed in just snug.

Let me know how it goes with the RAVE, than try the Water Flow Regulator valve, if it didn't change.

Karl
 
I took it out today...

it still runs up on it's own. I'll put it back in the garage and try that water flow regulator.
 
Hi, just a thought, 18mph might be right on the rev limit of when the power valves start to open.
I found that when i am using the boat for wake boarding, i sit on 22mph and it was just on the limit, sometimes it would pop the rave and the speed would increase with no input.
I found i had to turn the red plastic adjusters in all the way to stop the raves from opening at this speed, after adjustment it was perfect and sat at 22mph with no probs!!
 
As far as i know it doesn't matter where you have them set.
If you have them all the way in the raves will open later, if they are all the way out the rave will open sooner.
This will efect the powerband of the motor, but in your case i think you could use it to get the speed to stay where you want.
I have mine all the way in, but have run all the way out(level with the top of the black plastic) when i want them to open earlier.
 
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Took the boat out today...

Problem is still there...actually seems much worse (or at least worse than I remember). I would set speed about 18-20 mph, boat would be just up on plane, then it would TAKE OFF, engine rpms would climb, and boat would accelerate very rapidly, up to about 35+ MPH. Backing the throttle off, just a touch, would immediately hear the engine rpms drop (almost "bog" sounding), and speed would drop to below plane, about 7 mph.

Tried something else too. If I pushed the throttle to full and let the boat reach full speed, the boat WOULD NOT slow down, no matter how much I backed off the throttle, until all of a sudden, wham, back to 7 mph...absolutely no in between what so ever if you started with full throttle.

I'm at my wits end. My boat has no throttle, just an ON/OFF switch!!!

Tim
 
Oh, and I checked the carbs/throttle cable. At full throttle, the carbs are wide open, back the throttle off a little, and the carbs start to close. In other words, I'm getting full range of motion on the carbs in proportion with the throttle.
 
I found the problem!!! But, need the solution....

Hurray!
I found the problem today, and it was what was first suggested: the power valves. I think I had a hard time figuring this out because I was thinking of this as a SPEED problem, and not an RPM problem. But, I took the boat out today and noticed that my boat WILL NOT, under ANY circumstance, run between (indicated) 4200 rpm and 6800 rpm. So, I disconnected the power valve vacuum leads and presto, the engine would run at any rpm I wanted, and could achieve any speed I wanted. I could even reach top speed (it just took about twice as long to get there).

Now I just need to find out how to trouble shoot the valve solinoid...
 
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