2001 GTX Carb - High compression on MAG cylinder

[Highmaster2]

Hi,

Have a 2001 SeaDoo GTX Carb Version (951). Started 2001 season with a new top end - standard bore. Also added:

An ADA Billet Head (155psi Domes)
Carbon Tech Super Stock Reeds (206SS)
Proks w/Outerwears
Removed Accel pump and rejetted for that and the Proks.

Ran smooth right up until end of season - started running a little rough but, since it was end of season I just pulled it out of the water. Winterized it and let it sit 'til now.

Now prepping for new season. One of the first things I did was re-torque the ADA head and check compression. Last year my gauge showed 150 psi on each cylinder. Considering the 155 psi domes and the variations in compression gauges I was happy with that.

I charged the battery and also attached a 12 volt jump box to the battery. I checked PTO cylinder first and it showed 150 psi. I then checked the MAG cylinder and it showed 180 psi. I first assume that there is something in the combustion chamber so I pulled the head. Both the head and the pistons looked brand new. I then reinstalled and re-torqued the head and checked the compression again. Still showed 150 & 180. This time the RAVEs were both out. Definitely more pressure escaping through the MAG RAVE slot than from the PTO slot.

Each of the pistons comes up just short of the top of the cylinder before starting back down. I remove the domes and thoroughly clean all the surfaces where the domes meet the head. I then replace the o-rings and reinstall the head. Still showing 150 & 180.

I remove the head and swap the domes. Reinstall the head. Still showing 180 on the MAG cylinder.

I'm stumped. Anybody ever seen anything like this? Not sure what to try next.

Any insight or assistance would be greatly appreciated.

Thanks!

 

[mikidymac]

As the rings don't seal on the RAVES they should not effect compression.

Never use a booster or jump pack on these.

IF everything looks fine and there isn't oil or water in the combustion chamber then there is no way for the compression to go up 30 psi. I would check with a different gauge, it might not be that the MAG is 30 psi high, it could be the PTO is 30 psi low. This would explain the crappy running. IF it was me I would be checking the PTO for issues.

 

[Highmaster2]

Waiting on another gauge. Will update ASAP.
Thanks!

 

[Highmaster2]

Ok. $150 and another gauge later, I'm still stumped. The new gauge read exactly the same as my old one.

I contacted ADA Performance. I advised that I knew their head wasn't the problem since I switched the domes and the compressions stayed specific to each piston, but asked if they had ever run into anything like this. They advised no, but suggested that I fire up the engine on the hose, let it get up to operating temp, let it cool back down and check the compression again.

Will be a few days before I can do that and I'll update then.

Hope everyone has a safe and enjoyable Memorial Day weekend.

 

[Highmaster2]

PS... Found access to a source of 250 psi of air pressure. Attached new and old gauges. Both showed within 1 psi of 250.

 

[Highmaster2]

OK... Followed ADA Performance's suggestion. Ran Doo on the hose until the head was too hot to touch. Let it cool down completely. Rechecked the compression. 150 psi on both cylinders, with both gauges.

More confused now than I was before. Don't understand how that would have changed the compression reading, but something did change.

I'll put it in the water Monday and see how it runs.

mikidymac... thanks for the response and the insight!

 

[mikidymac]

OK... Followed ADA Performance's suggestion. Ran Doo on the hose until the head was too hot to touch. Let it cool down completely. Rechecked the compression. 150 psi on both cylinders, with both gauges.

More confused now than I was before. Don't understand how that would have changed the compression reading, but something did change.

I'll put it in the water Monday and see how it runs.

mikidymac... thanks for the response and the insight!

Very strange indeed.

 

[Highmaster2]

Decided I would just add to this thread instead of starting a new one. As a reminder, this is a 2001 GTX carb version 951. New top end - standard bore. Also has:

ADA Billet Head (155psi Domes)
Carbon Tech Super Stock Reeds (206SS)
Proks w/Outerwears
Solas Concord ST-CD-15/20 Impeller
2 Degree Pump Wedge
Removed Accel pump and rejetted for that and the Proks
Main 167.5 / Lows 95 / Mikuni N&S= 2.3 / Popoff = 25 / HS=1 out / LS=1 1/2 out
New NGK plugs last week

Verified that TPS drops to 0 volts at ~80% throttle. Feels like RAVEs open at about 5,000 rpm. Compression 150 psi on both cylinders with 2 different gauges.

Starts easily. Idles smoothly. Doesn't load up even in long No Wake zone. On slow, steady acceleration, slight intermittent sputter up to around 3,000 rpm. Past that very smooth up to just over 6,500. If I nail the throttle from idle, it tries to stand straight up and pulls very quickly and strongly up to 6,000 then creeps up to just over 6,500 (52 mph on GPS speedo).

Relatively new fuel and vent lines all through it. Fuel selector was replaced last year. Every tank of gas has Marine Sta-Bil used in it.

Thoughts on what should I look at next to try and get it to run up to 7,000 rpm?

Thanks much for any wisdom anyone might be willing to share.

 

[JC-SUPERJET]

For a quick test, you could back the Ski on the Trailer into the Water and at Full Throttle, manually pull the RAVE Valves fully open/up.

If you gain RPM, then the Solenoid Valve/Hose that feeds the RAVE Valves is leaking or going bad. This Solenoid System allows Crankcase Pressure to push the RAVE Valves up but is controlled electrically by the MPEM(?).

There is also a Check Valve in this System that can go bad too.

Many eliminate/bypass this Solenoid Valve and use straight Exhaust Gas to actuate the RAVE Valves.

Much simpler, reliable and direct.

 

[Highmaster2]

I don't really have a ramp that's convenient. Would it be stupid to try this with the Doo tied to a dock by the ring where you attach a tow rope?

Or, I guess I could disconnect the power to the RAVE solenoid and see if it runs same, better or worse.

 

[JC-SUPERJET]

With no Power, the RAVE Solenoid is Normally Closed, so that won't work as far as lifting the RAVE Blades for maximum RPMs...

 

[mikidymac]

The trick back in the day was to cut an oval hole in the cap with a dremel so that you could visually see when they were opening with the seat off. Might be worth a try.

 

[Highmaster2]

Got ambushed by covid a few days ago. I'll update again when I'm able to play with it some more. I figured next thing I'll try is to unplug the RAVE solenoid connector and see if there's any perceptible difference.

In case I'm not back before then, I hope everyone has a safe and enjoyable time on America's 246th birthday!

 

[Highmaster2]

Just a question while I'm waiting to get out of the house again...

If you bypass the RAVE solenoid and drill the RAVE housings to get the pulses directly from the crankcase, do you use the same springs under the RAVE caps, or something different?

 

[JC-SUPERJET]

Was that a typo "Crankcase"? Many drill a small hole in each Rave Hosing/Base to allow EXHAUST to lift the RAVE Blades. And use the same Springs. This works really good.

In the Stock RAVE Actuating System, for normal riding and operation, your idea as written, will not safely work because the Rave Valves need to vent or "deflate" on the way down, This is done thru the Solenoid Valve. The Solenoid has an 'Exit" Vent on the Rear side that connects to a Hose that carries the "used" or "spent" Crankcase Pulse Air to a Vent Hole safely to Atmosphere. Remember that the Crankcase Air is actually mixed with Gasoline Vapors so it would be deadly to vent these Fumes into the Engine Bay.

Download ASAP a Free Seadoo Service Manual and look at the RAVE System Diagrams to see how the Crankcase Pulses travel thru the Rave System.

With the Exhaust System Method, the Raves "vent" Exhaust back into the Cylinder out the Main Exhaust Port, as the Rave Blades travel downwards under Spring tension.

The Exhaust Pressure is proportional to the Engine's RPM. So more RPM equal more Rave Valve Lift and vice versa.

So if you somehow locked the Valves all the way up, you would get more RPMS and Top End Speed, but would lose Bottom End response. And if you held the Valves all the way down(starting position), you would get great Bottom End response but anemic Top End Speed, which is what you are experiencing.

There is a Procedure available for converting to Exhaust Pressure.

 

[Highmaster2]

JC-SUPERJET...​

I apologize. Your narrative was clear, concise and to the point. Why I typed "crankcase" I will never know. I could blame it on the covid, but, in truth, I have to admit that it was just an acute case of cerebral flatulence.

But, seriously, I do appreciate you taking the time to respond as you did.

Hmmmmm... That head looks awfully familiar. Is it an ADA head? And your engine compartment looks very neat and professional.

Again, thanks for straightening me out (and answering the question about the springs).

 

[JC-SUPERJET]

Yes, ADA Head.

That 150 Hp Pump Gas 951 Engine was built by Mark McQueen and installed in an SXR 800 Standup Hull that did 62 mph all day long with brutal MSD Total Loss acceleration.

I was the Proud Owner-Operator for a few years till the Whiplash and the Elbow Tendinitis became unbearable.

About the same as riding a Jack Hammer...

 

[Highmaster2]

Ok. Finally got to play with the GTX some more. It runs extremely strong up to about 50 mph and then creeps up to a max of 52 on a GPS speedometer. This is about 6550 rpm. Just to recap, The Doo has these mods:

Solas ST-CD-15/20 impeller
2 degree pump wedge
An ADA Billet Head (155psi Domes)
Carbon Tech Super Stock Reeds (206SS)
Proks w/Outerwears
Removed Accel pump and rejetted for that and the Proks.
Mains: 167.5
Low Speed: 95
Mikuni 2.3 needle & seat
Popoff: 25
HS Screws: 1 out
LS Screws: 1 1/2 out

The wear ring to impeller clearance was still within spec so I didn't replace the wear ring.

I unplugged the connector on the RAVE solenoid and couldn't tell any difference. I then drilled the RAVE bases to allow them to get pressure directly from the exhaust. No difference.

I had checked the Throttle Position Sensor before I put it in the water and it was working correctly.

I am open for any ideas on where to look for the missing 500 rpm. Though, it just occurred to me that I probably need to disconnect the hose from the Water Regulator Valve and let it hang out from under the seat to see if it's reducing the water flow at higher speeds. I disassembled and cleaned the valve before I put it in the water. Everything "looked" good on it.

BTW - my goal on this is to have the Doo break 60 mph. Am I just expecting too much?

 

[mikidymac]

You are way down on speed and rpm.

A stock 951 GTX should be doing 6900 rpm and 57-58 mph at sea level.

 

[Highmaster2]

A follow up…
Still chasing the missing 500 rpm.

Routed the line from the WRV to the exhaust out from under the seat so I could see the amount of water. Started off at a full flow then tapered off as the rpm came up so it appears to be working as it should.

Changed HS screws from 1 out to ¾ out. No difference.

Clipped some off the plug wires (ends looked pretty burnt) and screwed the plug caps back on. No improvement. Should I do the same thing on the coil ends?

A couple of days ago I was pulling some people around on a towable. Pulled out with a couple of victims in the tube and it was struggling to get the Doo and the towable up on plane. I was not aware at that time that a seam had split and the towable cover was filling up with water. TryIng to get the Doo up to speed, I briefly went WOT. Engine revved to 6950 rpm.

Someone help me understand why it would turn 6950 with so much strain on it, but won’t turn over 6550 with just me on it.

Thanks for any wisdom and/or insight.

 

[POPPS]

Heres my scenario in 2004,,,preparing for havasu...I have 3 race heads for my 800 cc LTD,,,43 cc domes...93 octane,,,41.5 cc domes,,,100 octane,,,(87 and 110 VP),,,and revs 7750,,,yet when I did my testing,,,the 39 cc domes (straight 110),,would grunt quickly out if the hole,,,but would not rev out like the 41.5 cc domes,,,could be a timing curve issue,,,don't know to this day,,,we just run the 190 psi head and run perfectly,,,with a bit less "grunt" off the line...just ideas...