1998 GTX LTD Max RPM 5k

[val-e-vue]

I have completed the rebuild of two of these machines And have them in the water.

Both machines have freshly rebuilt 951 engines. The carburetor’s were rebuilt with Mikuni genuine parts and all documented tests were performed.

Both machines start and idle at 1500 RPM and accelerate smoothly and powerfully. The difference occurs at 5000-5200 RPM. One machine maxes out at this RPM and the other continues to 6500 RPM.

The slow-poke is very smooth, it’s not skipping and it doesn’t fall off. It maintains that RPM smoothly. However, you have another 1/4” of throttle that has little to know effect. Close inspection of the throttle and oil pump cable looks normal.

The low speed jets are currently at 1 3/4 turns and the high speed are both closed. Tweaking of the low speed has not yielded any improvement. Not really surprised since the low end and transition seem very good.

I would like to try the high speed, but I’m not even sure I can get to it in the machine. I thought before I did anything crazy I would get some expert advice on how to proceed.

Thanks!!

 

[mikidymac]

I would check your RAVE valves, sounds like they might not be opening.

Also you can’t hurt anything by going richer on the screws. The only thing that might happen is fouling a spark plug.

Also the low screws will do nothing for your top end issues as they only adjust the idle mixture.

 

[val-e-vue]

What’s the best way to check my RAVE valves? When they were off the machine, I cleaned them and if I remember right they activated using pressure. I guess the spring held them closed and when I applied pressure (low) they would open. However, I recall that they require steady pressure... meaning they bleed off automatically.

Maybe you can confirm if that is normal and give me some ideas on further testing. Especially if there is something beyond bench testing.

Thanks so much for your help!

 

[val-e-vue]

I took the RAVE valve covers off and inspected. They look good and I can operate them with manually. I also inspected the hose from the engine base to the solenoid valve. It’s definitely connected and I tried to verify that it’s not pinched. All connection points have tie wrap clamps.

I completely buy into the RAVE valve theory, it matches my symptoms... makes sense. So I will have to pursue this more. It’s really tough in the working in the water.

Is it unusual to have trouble with the solenoid or the check valve? My gut has me thinking the check valve could be preventing reaching the pressure level required to fully withdraw the blade. Just theorizing... but if this is a common issue, I might be able to pull that out. It’s somewhat accessible. Are they serviceable?

 

[etemplet]

You can test the solenoid electrically. The check valve can plug up. If you have a mitey-vac you can connect to the line going into the rave solenoid and pull a vacuum test. Are the raves assembled correctly? are the lines to the solenoid in thier proper places?

 

[val-e-vue]

You can test the solenoid electrically. The check valve can plug up. If you have a mitey-vac you can connect to the line going into the rave solenoid and pull a vacuum test. Are the raves assembled correctly? are the lines to the solenoid in thier proper places?

I think the RAVE valves are assembled correctly. I'm the same guy that assembled the ones on the other machine that works correctly. However, I'm not taking anything for granted... I make mistakes everyday!

I may take the solenoid out of the ski and take it home, we are renting a camp, and bench test it. I brought my mitey-vac out today, so if it calms down tomorrow I will do some testing of the check valve. You have given me an idea... My mitey-vac can operate as a vacuum pump or a pressure pump, therefore the gauge can easily be used to measure both. I will run some tests while driving the jet ski, measuring the pressure at the input of the solenoid and the output of the solenoid. I'm not sure what the pressure should be, but I can report back and some of you are apt to know.

I appreciate your help etemplet.

 

[val-e-vue]

I ran a couple tests this morning on the water. I remove the supply line from the solenoid and monitored the pressure. The pressure increases from 0psi to 7psi with rpms. I know from testing in the shop that this is more than adequate to actuate the RAVE valves.

I reconnected the supply line and moved my gauge to the solenoid output. This reading never changed, 0psi regardless of rpm, even at WOT. Now I need to get some paper clips and the proper leads for my meet and see if the solenoid is activated.

Does anyone know the conditions required for the MPEM to activate the solenoid?

 

[etemplet]

I've often thought of taking the ski out and using the Mitey Vac to actuate the raves at 5k RPM as a test. The rave solenoid is an easy test electrically as you can do it with the battery voltage and applying air pressure to the inlet tube. If it drops off when it opens, that part is working. I don't think it gets the full 12 volts in operation though. Might be more like 5 or 6 volts. Sounds like you found an issue. Good Luck with it !!

 

[val-e-vue]

The solenoid is not being activated. I had the meter
on the solenoid cable and nothing.... So I have up to 7psi to the solenoid, but the solenoid is never activated. Not sure where to go from here, but I did try something for the fun of it. I bypassed the solenoid and connected the crankcase line directly to the RAVE valves. The result was not that impressive... I only got an extra 500 rpm’s top end and the expected flat mid-range. Very surprised I didn’t get the extra 1500 on the top end.

I left it plumbed it plumbed this way, and the kids tried to pull a tube. It had no power, so I switched it back. Power is back but limited to 5k RPM.

Next step is to record the pressure readings on the fast machine and monitor the solenoid voltage.

 

[etemplet]

Could it be a "ground" problem causing it not to activate... OR, somethng the computer is looking for and not seeing?? Does this ski have the throttle cable that splits and has a sensor or contactor in it? If the computer is looking for that to click a switch and yours is bad that may be a problem I have that on my 2000 RX.

 

[Seadoo timebomb]

Swap the solenoid from other ski. This will confirm if working or not. Those skis should pull at least 6800 rpm when everything is correct.

 

[val-e-vue]

Could it be a "ground" problem causing it not to activate... OR, somethng the computer is looking for and not seeing?? Does this ski have the throttle cable that splits and has a sensor or contactor in it? If the computer is looking for that to click a switch and yours is bad that may be a problem I have that on my 2000 RX.

This ski doesn't have the split with sensor. There is no throttle position... just a dumb cable.

I will update momentarily with what I have found by studying the good/faster ski. It doesn't seem to be a wiring or ground issue and the solenoid valve works if I provide power to it directly from the battery.

Thank you!!

 

[val-e-vue]

Ok - I was delayed by the storm that passed through here. Jet skiing was out of the question, at least for a guy my age

Once things settled down, I ran a couple tests on the "fast" ski. Ironically I found that ski had no pressure on the RAVE supply line from the crankcase. So I went ahead and replaced the check valve with a new one, I had ordered two of them last week from OSD. With the new valve in place, I was getting the 7psi at RPM's above 4K. I then tested the signal to the RAVE solenoid and it was very repeatably activated at 6K RPM.

The fact that the "fast" ski had a bad check valve, really muddied the waters, but it did make two things clear. 1) These skis can turn close to 6500 RPM's without the RAVE system working. 2) The "slow" ski doesn't turn enough RPM's to activate the RAVE solenoid since it only turns 5500 RPM tops.

Fast Ski Next steps: Later this evening I will test the top RPM's to see if it improves the peak RPM from 6500 or if it gets there more quickly etc. Remember, I was thrilled with this ski before!!

Slow ski next steps: I'm guessing that I may need a high speed jet adjustment. It is currently closed. Honestly I can't seem to see the high speed jets while the carbs are in the ski and the sun is shining in my eyes. Are they adjustable in place? Are they on the bottom of the carb? Any advice here would be greatly appreciated. I bought an endoscope but it's useless in the full sun because you can't see your phone. I think in my garage it could be useful.... but I don't have water in my garage

Appreciate you guys hanging in there and helping out!

 

[Seadoo timebomb]

If motor doesnt have enough case pressure then it is junk. So rule that out if they are newish. Rave solenoid usually activates around 5000 rpm. At 5500 the raves are open and motor should rev up to at least 6800. Most any decent running 951 will get more, If someone has changed the oem prop out, could give some of these symptoms. But there are other things not right.

Even when raves are not opening up, motor will see 6300-6400 rpm.
Leave high speed needles alone. They are supposed to be shut.

You have something totally jacked up for the numbers you are getting. Likely overlooking something obvious, but without hands on is hard to say. The 98 GTXL is the fastest of all 951 GTX skis. But you are no where close to having those running right.

Has this ski had any problems of just dying when running at speed? Then start back up?

 

[val-e-vue]

If motor doesnt have enough case pressure then it is junk. So rule that out if they are newish. Rave solenoid usually activates around 5000 rpm. At 5500 the raves are open and motor should rev up to at least 6800. Most any decent running 951 will get more, If someone has changed the oem prop out, could give some of these symptoms. But there are other things not right.

Even when raves are not opening up, motor will see 6300-6400 rpm.
Leave high speed needles alone. They are supposed to be shut.

You have something totally jacked up for the numbers you are getting. Likely overlooking something obvious, but without hands on is hard to say. The 98 GTXL is the fastest of all 951 GTX skis. But you are no where close to having those running right.

Has this ski had any problems of just dying when running at speed? Then start back up?

Both skis are running stock props and the wear rings are fresh. I would say the props are in equally good condition. Like I say the "fast" ski would rev 6500 without the RAVE valves (disconnected). Now that I replaced the check valve in the RAVE supply line, the engine will rev 7K and it is much more aggressive in that 5500 to 7000 range. Like I said before, the RAVE solenoid seemed to activate at 6K but now that everything is working I can't tell if it's 5500 or 6K. Honestly I'm busy holding on!! and Looking ahead

So I 100% satisfied with the "fast" ski... it's crazy fast now!

The "slow" ski is puzzling. It's all fresh... built at the same time. Need to find the difference.

 

[val-e-vue]

........

Has this ski had any problems of just dying when running at speed? Then start back up?

No, both skis start and idle perfect and accelerate and run at full speed. If you only owned the "slow" ski and never had experience with the "fast" ski, you would think it was fine.

 

[Seadoo timebomb]

Compare your pulse line pressure between the two. Eliminate that. Swap the solenoids, Eliminate that. Swap mpems, Eliminate that. Check to make sure the big exhaust hose is not soggy feeling on the slow ski.

Quickest swap is the mpem. That should eliminate most of it being electrical.

Are both spark plugs equally hot after riding?

Is there any signs of smoke when seat is taken off?

Remove the rave springs and do a test ride.to make sure they are opening.

You might also swap the water injection RAVE valve on water box. No need to disassemble, just swap them over and see if any difference.

Were the engines original that got rebuilt or exchanged? Was the timing checked? Do the timing numbers stamped on crankcase match the correction factor with mpem?

Compare temps on different parts of the pipe to the fast ski. You can do it by feel. They should both very very warm but not too hot to touch. Look at both sets of plugs to see if they look the same.

When carburetors were apart did you check the number sizes on jets? Just in case someone may have installed after market flame arresters and then just swapped out without changing jets back.

There are three combinations for jet sizes usually found in the 98 models.

Low 82.5 High 162.5 Low speed needle 1 1/4 open High shut
Low 80 High 160 Low speed needle 1 1/2 open High Mag shut PTO 1/4 open
Low 75 High 162.5 Low speed needle 1 1/2 open High shut

When that ski is running correctly, the throttle response will rip evenly hard from dead stop all the way to max rpm. You should be able to get 59 mph(real gps not speedo) on fairly smooth water. 6850 is usually the rpm I expect to see on LCD gauge running a completely stock ski.

 

[val-e-vue]

This will keep me busy for awhile!! Thank you! Great info and well organized

Let me answer the questions and work on the list of "to dos".

"Compare your pulse line pressure between the two"
I have compared the RAVE supply line between the two and they are similar (7psi). How do you do that, since it will toggle from vacuum to pressure as the engine rotates? Do you install a tee with a check valve? It seems like you would need to take pressure readings with the check valve pointing one way and then flip it to take the vacuum readings.

"Is there any signs of smoke when seat is taken off?"
No, neither ski has any signs of smoke inside the hull.

"Were the engines original that got rebuilt or exchanged?"
Both engines are original. My brother and I did everything except the machine work.
I sent the "slow" top end to Full Bore for machining and they bored it to 1.00 over.

I re-sleeved the "fast" ski and then took it to our local VT Engine shop. They bored to STD and honed. I did the filing of the ports before reassembly.

I rebuilt the carbs on both skis with Mikuni kits and bought new Mikuni needle and seats.

"Was the timing checked?"
No, When I removed the rotor from the flywheel, I marked the alignment and just made sure it went back together the same way. I never touched the stator or trigger coil.

"Do the timing numbers stamped on crankcase match the correction factor with mpem?"
I don't know. I was not aware of them so I never looked for them when the engine was out.

"When carburetors were apart did you check the number sizes on jets?"
I think I only checked the number on the seat of the needle and seat. Both skis have stock flame arresters.

--------------
I will work on the other questions that require investigation.

Thanks Again!

 

[val-e-vue]

Compare your pulse line pressure between the two. Eliminate that. Swap the solenoids, Eliminate that. Swap mpems, Eliminate that. Check to make sure the big exhaust hose is not soggy feeling on the slow ski.

Quickest swap is the mpem. That should eliminate most of it being electrical.
..........

Today I swapped out the MPEM, no change.

To complete the swap of the ignition system, I swapped spark plugs and the rear electrical box since it holds the ignition coil. Spark plug wires go with the box so it's fairly thorough test. However no improvement.

I have done temperature testing on everything using my hand and using an infrared thermometer. I don't see any significant difference. The spark plugs are around 125F and the exhaust and top end surfaces are slightly cooler.... maybe 120. That's after WOT run and taking time to get the seats off etc.

I also checked the large exhaust hose which seems the same on both machines. They are quite pliable but they don't get very hot. I wasn't exactly sure what soggy meant. Main point is they are both the same.

My next move will be the entire RAVE system. I will have to move it from the slow ski to the fast ski since the slow ski is 1.00mm over and the fast ski is STD bore.

Thanks, Gregg

 

[val-e-vue]

Compare your pulse line pressure between the two.....
...
When carburetors were apart did you check the number sizes on jets? Just in case someone may have installed after market flame arresters and then just swapped out without changing jets back.

There are three combinations for jet sizes usually found in the 98 models.

Low 82.5 High 162.5 Low speed needle 1 1/4 open High shut
Low 80 High 160 Low speed needle 1 1/2 open High Mag shut PTO 1/4 open
Low 75 High 162.5 Low speed needle 1 1/2 open High shut

When that ski is running correctly, the throttle response will rip evenly hard from dead stop all the way to max rpm. You should be able to get 59 mph(real gps not speedo) on fairly smooth water. 6850 is usually the rpm I expect to see on LCD gauge running a completely stock ski.

I'm back home with the skis. I have the slow ski in the garage and have ran a few tests that were difficult while in the water.
1) Checked compression using a Craftsmen compression tester.
Engine cold, both plugs removed, WOT, cranked for 10 secs
Mag: 135 psi
PTO: 140 psi

2) Checked the pulse line while cranking. It toggles between 2 psi and 5" Hg. We know from my water tests that it reaches 7psi at higher RPM, since that is what I read on the RAVE supply line. Not sure about the max vacuum level.

3) Removed the carburetors. Checked jet sizes.
Low: 80
High: 160

Here are photos of the spark plugs:
Mag: Darker
PTO: Lighter

I also noticed after removing the carbs that the gasket on the mag side was a little dinged up and the lower pin was deformed. It came back to me that I had wrestled with the carbs during installation. Gaskets ket falling off etc. In the end everything laid flat and the bolts were good and tight (full disclosure). When I reinstall, I will use new gaskets.

Gregg

 

[Stealth800]

I'm back home with the skis. I have the slow ski in the garage and have ran a few tests that were difficult while in the water.
1) Checked compression using a Craftsmen compression tester.
Engine cold, both plugs removed, WOT, cranked for 10 secs
Mag: 135 psi
PTO: 140 psi

2) Checked the pulse line while cranking. It toggles between 2 psi and 5" Hg. We know from my water tests that it reaches 7psi at higher RPM, since that is what I read on the RAVE supply line. Not sure about the max vacuum level.

3) Removed the carburetors. Checked jet sizes.
Low: 80
High: 160

Here are photos of the spark plugs:
Mag: Darker
PTO: Lighter

I also noticed after removing the carbs that the gasket on the mag side was a little dinged up and the lower pin was deformed. It came back to me that I had wrestled with the carbs during installation. Gaskets ket falling off etc. In the end everything laid flat and the bolts were good and tight (full disclosure). When I reinstall, I will use new gaskets.

Gregg

I'm back home with the skis. I have the slow ski in the garage and have ran a few tests that were difficult while in the water.
1) Checked compression using a Craftsmen compression tester.
Engine cold, both plugs removed, WOT, cranked for 10 secs
Mag: 135 psi
PTO: 140 psi

2) Checked the pulse line while cranking. It toggles between 2 psi and 5" Hg. We know from my water tests that it reaches 7psi at higher RPM, since that is what I read on the RAVE supply line. Not sure about the max vacuum level.

3) Removed the carburetors. Checked jet sizes.
Low: 80
High: 160

Here are photos of the spark plugs:
Mag: Darker
PTO: Lighter

I also noticed after removing the carbs that the gasket on the mag side was a little dinged up and the lower pin was deformed. It came back to me that I had wrestled with the carbs during installation. Gaskets ket falling off etc. In the end everything laid flat and the bolts were good and tight (full disclosure). When I reinstall, I will use new gaskets.

Gregg

 

[Stealth800]

Just curious of what the fix was?

 

[mikidymac]

Compression is good.

White plug looks lean. Was that the same cylinder that had the bad carb gasket?

 

[val-e-vue]

Just curious of what the fix was?

It's been a year, we are back at the lake for our 3 weeks. I never solved the problem. I tried one other thing this year but it made no difference. I bypassed the gas supply valve and the filter in case there was a restriction.

I still have a slow ski and a fast ski. They both start and run great but one turns 6500 RPM and the other only 5500 RPM. I make the younger kids drive the slow ski lol.

The only thing I haven't swapped between the skis are the carburetors. It's a tough experiment and I hate to mess up the fast ski. I have removed the slow ski carbs and repeated the testing, including the pop-off test. I think I mentioned in a previous post that I replaced the manifold gaskets during that process. No change.