Low compression - overheating - fouling plugs. HELP!! (96 SPX)

[k_dog345]

I’m trying to wrap my head around what the heck is going on with my ski. I have several questions I hope to get answered, I’m starting to go crazy trying to figure it out! This is the first time I’ve really worked on a jet ski, so forgive any ignorance - I’m still learning!

List of things I’ve done:
- rebuilt carbs, with genuine Mikuni parts
- put on “new” used carbs that were built with genuine Mikuni
- all grey fuel lines replaced
- carbs are set to stock. 1 1/4 L, 0 H

Compression reads 120psi both cylinders and has since I’ve had it the last three years. It ran fine, but I realize this is low so I have new jugs coming to me.

SYMPTOMS:
I got excited after installing new carbs because throttle response was crispy again. But as I ran it more, I’m experiencing the same issues I’ve had.

1) Bogging happening from idle to 1/4 throttle. Once it hits the powerband it runs great. Performance degrades on maneuvers at times. Observing at idle, it seems like it will load up and bit and RPMs slightly drop, but it’ll get past it on its own without touching the throttle

2) And it seems like I’m running hot, but alarm isn’t going off. Head/exhaust gets too hot to the touch after shutting off from higher rpms but seems to eventually cool down. But it has got hot to the point the buzzer was screaming at me. This picture shows my pisser at full throttle. Does this seem weak?


Here’s a video that demonstrates bogging and pisser:

3) Spark plug checks show a lean condition when using full throttle and shutting off immediately.


4) last outing my battery didn’t charge
EDIT: I'm not sure this was the case, I think my motor seized and I couldn't crank over. I just thought it was the battery....

This last outing I stalled after using full throttle briefly. I could not restart after this, had to paddle back in. I freaked out thinking that maybe I blew my motor (EDIT: my motor is actually seized), but I think my plugs got fouled (why would a seized motor show black plugs like this?).




I've been running with damage on my bottom end, but I’m not sure it’s significant enough to cause any issues (AS FAR AS I KNOW!) My rotary valve cover took most of the damage, I did replace it. But I left the case ALONE
Case (left as is):


Rotary valve cover that I replaced:


My theory on this:
- low compression causing bogging/fouled plugs and degraded performance
- I’m thinking that maybe my cooling system is partially restricted, but I don’t know what the flow should look like from the pisser
- after my last outing maybe my stator is bad? Because my battery didn’t charge....or battery has just died
- I have no idea why my spark plugs read lean after full throttle....I could use some input on this.


QUESTIONS:
1) First and foremost, what route would you guys take in order to resolve these issues? Does my theory sound correct?

2) does my cooling system appear to be working properly? And what tips and tricks do you guys have to check/clear it

3) what is an easy test to ensure temp sensor/buzzer is working?

4) why the heck am I showing lean at WOT? Would you guys recommend that I richen high speed screw? Carbs are set to stock

5) why am I bogging at low RPMs and fouling plugs?

6) does my pump seem loud? What symptoms would a bad pump cause? I didn’t think of the pump being an issue but a guy on Facebook suggested it after posting this video:

MY PLAN:
Subject to change depending on the responses I get
- EDITED: replacing motor
- if this doesn’t resolve my issues, I’ll go through the entire fuel system AGAIN. Replace all the fuel lines, fuel selector, clean fuel strainer, rebuild carbs with genuine Mikuni and reinstall (EDITED: break down and cry)


I really appreciate the help anyone can provide, I hope I can finally put these issues to rest and have a good running ski....

 

[Pwnage1337]

As pump efficiency decreases the cooling system flow/pressure should also reduce. If you suspect you have pump issues, I would sort that out before throwing a top end on it and potentially ruining it because of lack of cooling. Could have plugged passages in the pump? My pisser doesn't shoot like a firehose but there is good flow coming out of it under throttle. I'd start with checking the wear ring, impeller condition, perhaps take the cooling line inlet and force some compressed air through the system VERY LIGHTLY, not a lot of pressure. Don't want to blow seals out. You could also just have a small piece of debris in the fittings of the pisser line. The passages aren't very big. Would be easy to remove and check.

If the pump is mechanically binding, it would cause low RPM issues as the engine is trying to overcome load that is present that should not be there. Once the engine moves into its powerband it would be less noticeable.

You can test the buzzer by grounding the sensor wire with the key on. Put the cap on the DESS post, then run a wire to the sensor wire to ground and it should beep. I don't know how to verify if the sensor itself is working but i would guess it grounds when it gets to a certain temperature.

As far as the lean condition under WOT, you might have an air leak in the case of the engine. Which would also contribute to the weird things going on with the carbs. If the pulse line from the case to the fuel pump is not operating under an ideal condition due to the case leaking air when it should be holding a vacuum, you could have fueling issues like a lack of fuel because of lack of vacuum to the pump to supply the carbs.

Did you replace the water separator when you went through the fuel system?

 

[k_dog345]

As pump efficiency decreases the cooling system flow/pressure should also reduce. If you suspect you have pump issues, I would sort that out before throwing a top end on it and potentially ruining it because of lack of cooling. Could have plugged passages in the pump? My pisser doesn't shoot like a firehose but there is good flow coming out of it under throttle. I'd start with checking the wear ring, impeller condition, perhaps take the cooling line inlet and force some compressed air through the system VERY LIGHTLY, not a lot of pressure. Don't want to blow seals out. You could also just have a small piece of debris in the fittings of the pisser line. The passages aren't very big. Would be easy to remove and check.

If the pump is mechanically binding, it would cause low RPM issues as the engine is trying to overcome load that is present that should not be there. Once the engine moves into its powerband it would be less noticeable.

You can test the buzzer by grounding the sensor wire with the key on. Put the cap on the DESS post, then run a wire to the sensor wire to ground and it should beep. I don't know how to verify if the sensor itself is working but i would guess it grounds when it gets to a certain temperature.

As far as the lean condition under WOT, you might have an air leak in the case of the engine. Which would also contribute to the weird things going on with the carbs. If the pulse line from the case to the fuel pump is not operating under an ideal condition due to the case leaking air when it should be holding a vacuum, you could have fueling issues like a lack of fuel because of lack of vacuum to the pump to supply the carbs.

Did you replace the water separator when you went through the fuel system?

I'm not sure the pump has any issues, I think the clanking noise when turning PTO by hand is normal and the resistance I felt came from the magneto. However, when installing the driveshaft, I do have to 'push up' on it to get it to fit to the pump. I did an engine alignment and everything was good there.... Maybe my drive line warped? Might be worth replacing it if so, any tools out there I can use to check?

I took your suggestion, and blew all my cooling lines. Did not notice any debris coming out of the lines, and it felt like the air was flowing pretty smoothly. Really hard to tell once I blew the exhaust hose. Seemed that inlet from pump was clear which I assume would be most important. Last time I got hot, exhaust cracked... so hopefully, that part is clear.

Thanks for suggestion on the buzzer, I'll give that a shot.

Regarding my lean condition, I've wondered this.... I've bought some starter fluid. I'll try spraying around carb base gaskets, lower case, etc to see if I notice any increase in RPMs. I hope not.....

I did replace the fuel strainer when going through my fuel system.

 

[k_dog345]

screw it, I'm getting a new engine. I broke down, started pulling things apart and decided it's just time to rebuild. Thanks for the help so far! I'm in too deep to give up on this thing now.

 

[POPPS]

I will quickly comment,,,the damage on your rotary valve face on the engine case, is the result of metal filings/pieces getting stuck between the rotary valve plate itself and the case face,,,.that metal no doubt has come from the bottom end,,,or top end,,,piston skirt,,,part of a ring,,,Just,,,pull'er apart.

 

[k_dog345]

Stiff rod bearing (seized engine). Damn it.....




Well I guess now I’ll take a chance on an SBT motor. I see a lot of mixed reviews, but I really want to get this motor back in the ski ASAP while I still have some warm weather left. Wish me luck.....

 

[Pwnage1337]

Put one in my ski this year and it's been great... Just started bolting on go-fast shit so we will see how it holds up

 

[k_dog345]

Well this is why I stalled and could not restart last outing. My motor seized up out there. This is the next day after having heads off and checking that starter would turn over:

This is the moment my motor completely seized. Shortly after ending the video

I have a new motor coming but really don’t want to f$&@ up this one. Why would this have happened?

I will be sure to verify oil pump operation and keep a close eye on my spark plugs when I break the new engine in.....

 

[k_dog345]

Taking a look at this: Piston Diagnostic Guide. I definitely have the 'black spot hot' condition, there are black marks on the underside of my piston. This guide states either a lean fuel mixture, or cooling system failure. It seems like I might be dealing with both?

I have a newly rebuilt jet pump coming my way, so that will rule out a pump issue. Hopefully my pisser will start showing me a stronger stream. As stated above, I was pulling white plugs after running WOT. So maybe I need to richen my high speed screw as well? I had it set to stock after rebuilding with geniune Mikuni parts......Thoughts?

 

[k_dog345]

Check this out! PTO side, tons of metal shavings in case....MAG side, nothing....

 

[POPPS]

When you change the plugs on a normally running engine,,,initially they will be white...after some running time they will transcend to their colour of a pint of beer,,,light brown!

 

[k_dog345]

When you change the plugs on a normally running engine,,,initially they will be white...after some running time they will transcend to their colour of a pint of beer,,,light brown!

thank you for that insight...this is what I was doing. New plugs, full throttle briefly, shut off while wot, pulled them and they were white....that lead me to believe I was running lean WOT... so what’s the right way to checknew plugs for tuning carbs? I guess I had no idea what I was doing and something else has been my issue here. Running hot has been a common theme, could my bottom end simply just started failing?

 

[POPPS]

The high speed screws come from the factory at 1/4 turn out, with a plastic cap,,,the only way in,,,is in,,,to get slightly more top rpm...maybe 70 rpm tops...of course BRP did that so owners won't seize their Pistons at WOT.

 

[k_dog345]

Ok, thanks @POPPS I appreciate the info. I'll be sure to richen the high speed screws 1/4 of a turn. I had it set to stock at 0 turns. I'll leave low speed at 1 1/4

 

[k_dog345]

Thought I’d give an update! I was chasing my tail on this.

After installing a new motor, and observing the old one. I believe my crank was just going bad. When I sunk my ski in salt water way back last year, I didn’t know what I was doing and tried to start with a hydro locked motor too many times. I think that caused my seals to begin going bad/started process of bearings wearing out. They finally gave. I think my overheating problem was from friction of a bad crank. Feel free to correct me if you think my theory is wrong.

New motor in, this thing runs like a BEAST and I’m having a blast! It’s been a fun learning process, and this forum (along with you kind folks) have helped me tremendously.

I hope you all enjoy the rest of the summer season on the water [emoji41]

 

[mikidymac]

Glad everything is working well for you.