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1997 Seadoo Speedster RPM drop at 4k

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drizzie88

drizzie88

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Recently bought a Speedster and it seems like for every hour I have it on the water, I work on it for another four...

This time, I think I may have more problems than I can fix myself. Seeking the guidance of all you awesome garage mechanics out there!

On our way home, one of the top left water hose blew off the port side engine and it overheated. The engine shut down and we limped back on one engine. It got hot enough to darken the paint on the purple exhaust tube.

During troubleshooting, we found the blown hose, replaced the connector, ran it up and everything seemed fine. We had a leaking gasket around the spark plug, I ordered those and replaced all the top end seals. We then took it back on the water and the engine, under load, will not go above 4k RPMs... It maxes out at 4k and then drops back down to under 3k. The other engine runs fine.

When you fire it up at home with a hose connected, it runs fine above 4k, but on the water it will not. I'm wondering where I should go from here... I have moderate experience as a mechanic, but I'm by no means good at this. Learning as I go.

The cylinder walls did not look like they had any damage from a warped cylinder, but I only took the top cover off to replace all of the gaskets. That's as far into it as I got.
 
First I would check compression and report back. 150psi is perfect and at 120 it's time for a rebuild or if there is more than a few psi difference between cylinders.

Since it overheated you need to see if you have any melted exhaust hoses leaking exhaust into the engine compartment or collapsing restricting flow.

Also could be dirty carbs and/or fuel system since your pistons look a little lean. Only use Genuine Mikuni parts for carb rebuilds.
 
mikidymac said:
First I would check compression and report back. 150psi is perfect and at 120 it's time for a rebuild or if there is more than a few psi difference between cylinders.

Since it overheated you need to see if you have any melted exhaust hoses leaking exhaust into the engine compartment or collapsing restricting flow.

Also could be dirty carbs and/or fuel system since your pistons look a little lean. Only use Genuine Mikuni parts for carb rebuilds.
Click to expand...

We checked all the hoses and replaced a couple that had melted. Also tightened down all the clamps that miraculously came loose after tightening them... This boat has a ghost or something.

I am having the compression checked on Monday. Finally got a mechanic to call me back. No one likes working in the hell-hole on these boats. This mechanic said he is going to help me troubleshoot but doesn't want to really work on it too much because he's old and it hurts his back to be in that position for a long period of time. So, we will check compression and report back. I think I'm going to rebuild both carbs this off-season (in between my deployment to Afghanistan)... Most of my winter is going to shot deployed so I may just have them rebuilt while I'm gone.

As far as the fuel comment? If the other engine is running alright, you still think it could be a fuel issue? I'll have to research what isn't common between the two.

My plan ahead:

Compression test
Rebuild carbs
Pray to the Seadoo Gods
 
Alright guys... I'm baffled here.

1. Compression checks on the bad engine 135-140 PSI on both cylinders.
a. Checked the good engine and it had same amount of pressure. Assume it's just the cheap compression tester I bought at AutoZone.
2. Carbs rebuilt this week by a mechanic.
3. Cut back the spark plug wires, have good spark.
4. New/Gapped plugs.
5. Changed the water drain tubes. They were full of sand. Good now.
6. Changed all the gaskets on the top end. Had a couple blown and water leaking around the spark plugs, but none got down in the cylinders.

As soon as the engine hits 4k, it drops down to idle (1.5k). If you cycle the throttle, it will hit 4k again and stay there, but as soon as you go past 4k it will drop back down.

It only happens on the water. With a hose hooked up to engine it will sit over 4k RPMs no problem.
 
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Is the charging system working properly? Should be 13 plus volts at the battery, just trying to eliminate easy to check items. However, it usually is fuel delivery related (carbs).
 
POPPS said:
Is the charging system working properly? Should be 13 plus volts at the battery, just trying to eliminate easy to check items. However, it usually is fuel delivery related (carbs).
Click to expand...
Battery is new (three months old) with a kill switch installed so nothing draining it. Other engine works fine.

Anyone know any good write ups on tuning the carbs and what each part does? I’m new to carbs and I need to learn more.
 
Miki has a carb thread, check it out. It will guide you. And as a side note, that clamp that miraculously loosened, happened to me, the internals of that hose collapse over time, and the next thing you know, it has blown off, even though you swear you tightened it. That cost me a top end before a race. ( I tightened it twice). Replace the hoses. I have had clamps that I thought were tightening, and were in fact stripped on one of the gear teeth. Replace the clamps for piece of mind.
 
POPPS said:
Miki has a carb thread, check it out. It will guide you. And as a side note, that clamp that miraculously loosened, happened to me, the internals of that hose collapse over time, and the next thing you know, it has blown off, even though you swear you tightened it. That cost me a top end before a race. ( I tightened it twice). Replace the hoses. I have had clamps that I thought were tightening, and were in fact stripped on one of the gear teeth. Replace the clamps for piece of mind.
Click to expand...

Thanks. I'll start searching. I'm almost at the point I'm going to have to just take this in and let a professional fix it...at the expense of my wallet.
 
Took the boat out yesterday. The problem child engine still doing the same thing after we did a couple of small less than notable things. Now, it doesn't feel like it is even giving any thrust at 4k. It used to sustain 4k RPMs but now it drops off more frequently and the problem has gotten worse.
 
Miki could be correct, when you blew off that hose, you could have (unfortunately), scored your cylinders, and therefore, require a top end rebuild.
 
POPPS said:
Miki could be correct, when you blew off that hose, you could have (unfortunately), scored your cylinders, and therefore, require a top end rebuild.
Click to expand...
What does a top end rebuild consist of? I changed all the baskets and seals on the top end last week. I forgot to add that to the list of things done.
 
I wouldn't worry about a top end unless you check your compression and it's low. 150 is perfect and at 120 you need a rebuild.
 
mikidymac said:
I wouldn't worry about a top end unless you check your compression and it's low. 150 is perfect and at 120 you need a rebuild.
Click to expand...

I was sitting at around 140 psi with a cheap tester on both engines.

Should I rebuild the carbs and go from there? I am legit lost.
 
drizzie88 said:
No. My uncle is going to help me rebuild the carbs in a couple weeks since I’ve never done it.
Click to expand...
POPPS said:
Miki has a carb thread, check it out. It will guide you. And as a side note, that clamp that miraculously loosened, happened to me, the internals of that hose collapse over time, and the next thing you know, it has blown off, even though you swear you tightened it. That cost me a top end before a race. ( I tightened it twice). Replace the hoses. I have had clamps that I thought were tightening, and were in fact stripped on one of the gear teeth. Replace the clamps for piece of mind.
Click to expand...
drizzie88 said:
I was sitting at around 140 psi with a cheap


(Just thinking outside the box), This may sound crazy, try switching the in fuel lines at the baffle. Is your pulse line secure and not cracked? Have ruled out the stator, and rectifier? Have you checked the front electrical plug for corrosion? Have you load tested that new battery?
Click to expand...
 
I have the same issue with a jetboat i just purchased. I have a 1996 dual rotax engine speedster and only the right engine fails at 4k RPM after less than an hour of running fine in the water.
 

I think we have found a problem today when we got off the water. We were checking the engine out and I pulled the aft wire off the plug while it was running (don't do it, you'll shock the shit out of yourself) and it died after about two cycles of the other cylinder. I did the opposite and it stayed running. I pulled the cover off of the MPEM box to see where those wires run to and they connect to an electrical box.

I'd like to replace those spark plug wires, but it looks like it comes as a unit and the electrical box is connected to them?

A couple of questions before I continue troubleshooting tomorrow:

1. Can I swap the plug wires and see if the problem continues or could that fry any of the electronics in the MPEM?
2. I want to just rebuild the entire carb. It seems like it isn't getting the proper fuel and here is why.
a. In Neutral, if you quickly adjust the throttle, it immediately floods itself and dies. It will start right back up though.
b. There is a delay in the actual response in the the throttle also and sometimes hesistation even up to 4.5k where it then bogs back down.
c. I don't think the "mechanic" I took it to really did anything to them...

Anyone have a part number or better idea of how to replace those spark plug wires?

Where can I find the best deal on a rebuild kit for these carbs? I hear "only buy mikuni" so that's what I intend to do.
 
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