Stumped

[Cruisinga]

'92 Superjet. Factory pipe, high compression head, otherwise stock under the hood. Has been completely reliable for 4 years.
Last weekend I jumped a wake and the ski immediately died upon landing. It will crank but barely runs, using the primer I can nurse it over to the bank.

It starts and runs fine out of the water, idle "feels" a little higher than normal out of the water. In the water it barely runs at all and needs the primer pumped to get above idle. I suspected a reed petal broke so I pulled the carb and intake off, but the reeds looked perfect.

The fact that I need to use the primer makes me think it is lean and there is a fuel delivery problem but I am not sure how impact could cause that? Suggestions?

 

[Jakobi86]

Cracked fuel pickup, something in fuel pump, n/s in carb... Could be a lot. If it seems fuel related, ask yourself what could have broke or moved when it landed hard that would effect fuel delivery


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[iangdesign]

4 years is quite a while for these engines. Have you checked compression yet? Might be time to pull it apart and replace some seals and gaskets.

 

[tor*p*do]

internal fuel filter could be plugged

 

[Vortex]

Bad coil/plug wires. Running fine out of water but terrible under load points to the coil or possibly cdi, that's less likely tho

I just had the same problem. Are the plugs wet? Compression good? Wet plugs=not fuel problem

It is strange that you say the primer will keep it running, wouldnt rule out a fuel issue entirely. Could check fuel pressure to ensure your pumps are good.

 

[smoofers]

I'd pull your head, could've roasted a piston. Either way a fuel problem could've led to this. When was the last time your carb was rebuilt? The rubber and plastic parts in the carb break down over time. I usually don't go past 2 seasons without a carb rebuild.

 

[Cruisinga]

Thanks for the tips. I did jump but it wasn't that "hard" of a landing. Also, my skis are at a weekend vacation house so they don't get ridden all that many hours each year. That is also part of the issue fixing it, I have to plan ahead with tools and parts.
I have never been in the carb of this superjet. I don't recall my Kawasakis having an internal fuel filter, I guess it is in the fuel pump?
For fuel pump parts do you guys order parts from OEM Yamaha parts supplier or direct from Mikuni through someone like SBT?


I am planning to-
Bring bore scope to check piston
Bring compression tester
Bring new spark plugs
Run it and check for wet plugs to identify potential ignition system issue.
What else should be on my list?

Thanks for the help!

 

[Vortex]

Thanks for the tips. I did jump but it wasn't that "hard" of a landing. Also, my skis are at a weekend vacation house so they don't get ridden all that many hours each year. That is also part of the issue fixing it, I have to plan ahead with tools and parts.
I have never been in the carb of this superjet. I don't recall my Kawasakis having an internal fuel filter, I guess it is in the fuel pump?
For fuel pump parts do you guys order parts from OEM Yamaha parts supplier or direct from Mikuni through someone like SBT?


I am planning to-
Bring bore scope to check piston
Bring compression tester
Bring new spark plugs
Run it and check for wet plugs to identify potential ignition system issue.
What else should be on my list?

Thanks for the help!

If it won't rev out under load and feels unrideable it is your coil. Typically the wirea are the part that goes bad.

Assuming compression is good...

Fuel issue will not usually act like that, if it's lean due to an obstruction it will just stall. Rich is blubbery and can clear out.

Try turning the high or low speed out a turn or more and if it doesn't change it spark is likely the issue

 

[Cruisinga]

Spark plugs looked fine but I changed them anyway.
I don't trust my compression tester beyond telling if two cylinders match, which they did.
I was able to get the ski up to speed by working the primer, so it is definitely a fuel delivery issue.
I checked pop off pressure and it is ~50psi, which seems high, however I have read that is the stock setting for superjets.
I also don't know how a jump could cause the pop off pressure to change, so my guess is that the landing may have compromised the fuel pump and it's not building enough pressure. Fuel pump looked fine except for the fuel filter was about 70% clogged but that wouldn't happen all of a sudden. New carb kit gets here tomorrow so we'll see if a clean fuel filter and rebuilt carb solves the problem.
Am I missing anything?

 

[Fro Diesel]

The fuel tank has to pressurize to deliver fuel. A bad one way valve, tank breather could be your issue.
It must let air in and not out (it will vent under extreme pressure, but you cannot tell unless you can suck a golfball through a garden hose)

Avoid thinking too much about 'what caused it' and knock out these maintenace items first. I had a n/s go bad after one long season, it happens.

 

[Cruisinga]

I would agree with you on the tank venting, but if the tank was not venting the primer would also not work. I also pulled off the fuel return hose while the ski was idling and fuel was returning to the tank. When I have experienced tank venting issues on other vehicles, it will usually run fine until a vacuum builds in the tank which tanks a little. This ski will not get to speed unless the primer is worked.

I'm not sure I follow you on the pressurization of the tank? Never heard of that.

Maybe I am thinking too hard but I am an engineer so it's in my nature for better or worse.

 

[Vortex]

I would agree with you on the tank venting, but if the tank was not venting the primer would also not work. I also pulled off the fuel return hose while the ski was idling and fuel was returning to the tank. When I have experienced tank venting issues on other vehicles, it will usually run fine until a vacuum builds in the tank which tanks a little. This ski will not get to speed unless the primer is worked.

I'm not sure I follow you on the pressurization of the tank? Never heard of that.

Maybe I am thinking too hard but I am an engineer so it's in my nature for better or worse.

Let us know how it does with the carb kit installed. Weak spark is the next thing to look at

 

[Cruisinga]

Neither of the springs that came in the kit match the existing spring. Spring on the right was in the carb, gave a pop off pressure of ~50. I installed the dull silver spring that came with the kit and got a popoff around 25.
Since it ran very well before this issue, it seems like I should stick with the spring that has been in there for years?