SJ dies under acceleration

[MTRHEAD]

Want to share an interesting experience.

1990 square nose I redid this year with all the normal race stuff from the era. Couple of motors. Mild superstock motor and a Lamey/RD cylinder, 8mm rad crank short rod, novi’s, setback pump, dry pipes, wet pipes, etc.

During the process of breaking in the second motor, the Lamey as I call it, (note probably had 5 hard hours of first motor) I hit a decent surf boat wake and the ski shut off. Started it back up and thought wonder why that happened? Cruised around at constant rpm as I recovered from the stall - I accelerated very hard and ended up going over the bars as the motor shut off in a nano second. Ouch into waves. I immediately thought I locked it up or something broke. Scared to restart from a shut off I waited about 15 seconds. Fired it up and away I got back up on plain and it died again. For the next 15 minutes the motor continued to immediately start and sometimes run for 2-3 minutes and die and other times would die as soon as the throttle was opened up. Note it would idle just fine (that should of been my clue to the real issue)

Got back to beach and checked everything. Compression good, plugs looked good, poured gas in clear bottle, caps, wires, No water in gas, took carbs apart, checked reeds. Started up and was snappy on trailer. Back into water and it ran for bit ok. Then it shut off under acceleration like a light switch.

I though ok my zeel is bad??? But I kept thinking it was mechanical because it happened mechanically when I hit that big wave.

Once home and after pondering for sometime what could be wrong. Note with the RD motor I had to put on a remote pump for carbs to clear exhaust tube since I was using an angled shortened manifold and V3’s. So I thought maybe something with fuel lines being pinched since it’s so tight. As I was going through the fuel system I checked the tank 1 way breather valve. It was stuck open!!!

Put in a tested good one way breather from my 14’ and ski runs like a champ!!!

Yes that was it. Some debri lodged or the bladder failed on the wake boat jump and was in/out of operation after than. Being a 32 year old ski I bet it was all dried up. That was one of the only parts I don’t think I changed. Murphy’s law!!
I will also spend the $15 when redoing an ancient ski every time now.

Hope this threads helps someone else

 

[MTRHEAD]

Good question. Probably close but the ski had at least 3-4 tanks through it minimum before the problem reared it’s ugly head

working on a new problem. Lack of charging

 

[MTRHEAD]

Does the Setback Pump eliminate/cure the Square Nose sliding during Hard Turns?

Yes it helps along with Destroyers, bottom work and pump cavity work and proper prop size.
Skat pumps move prop back 30mm. I used 08 driveshaft and made a 50mm wear ring to add. So I moved the whole setup back 50mm. Position related to hull is same as 08’+ sj

 

[Storbeck]

The valve was stuck OPEN?

 

[MTRHEAD]

The valve was stuck OPEN?

Yes and for a bit if time I believe it fluctuated from working to non working before it lodged fully open

 

[mthomps]

Does the Setback Pump eliminate/cure the Square Nose sliding during Hard Turns?

Its gonna sound weird but i think i have the cure. Get your body as far from the tray as possible. If your turning left hang yourself off the left as hard as you can without falling. Cant slide if the weights not there to make it happen.

Weird but it worked for me. Now its a parlor trick but itll make a square turn

 

[Storbeck]

Yes and for a bit if time I believe it fluctuated from working to non working before it lodged fully open

I'm not dumb enough to argue with a guy that has been around the block a lot more times than I have, but this is super surprising to me because I have run skis with no check valve at all, just a coil of hose for venting, to see if the tank pressure thing actually mattered and seen no issue. I never saw any reason why there would be pressure in the tank other than situations where there was in increase in temperature from when it was filled.

 

[MTRHEAD]

I'm not dumb enough to argue with a guy that has been around the block a lot more times than I have, but this is super surprising to me because I have run skis with no check valve at all, just a coil of hose for venting, to see if the tank pressure thing actually mattered and seen no issue. I never saw any reason why there would be pressure in the tank other than situations where there was in increase in temperature from when it was filled.

Interesting. Well maybe something to do with a remote pump and where it’s mounted? Down a little lower than carbs. But I have the same on my blaster and many many other skis over the years. Some guys mounted them between motor mounts.
I run 3 remote pumps on the side of my GPR and the carbs are way low and there is literally 50’ of fuel line between pumps, tanks, and vapor separator. The tank uses a stock one way valve

 

[fastgtfairlane]

Everytime I've had a bad one way valve or no valve I've had random fuel delivery issues. Not sure why. I talked to Alex on his krash he has a main jet instead of a one way and has no issues

 

[Storbeck]

Everytime I've had a bad one way valve or no valve I've had random fuel delivery issues. Not sure why. I talked to Alex on his krash he has a main jet instead of a one way and has no issues

That would imply that no check valve is needed, the main jet allows free passage of pressure in either direction, no?


The biggest thing for me is, what on earth would cause there to be pressure in the tank? Often there WILL be pressure in the tank because you fill it and the temperature increases which causes internal pressure, but it's not like the oem could count on that to happen for the function of the ski.

 

[MTRHEAD]

All Liquids have their own natural Vapor Pressure.

When Temperature increases, the Vapor Pressure also increases.

Sloshing and Shaking of Gasoline ALSO increases Vapor Pressure by adding Kinetic Energy to the Fluid.

So riding a Jetski cause the Gasoline to slosh around and increases the V.P. resulting in higher Internal Fuel Tank Pressure, provided it's trapped in the Tank and not vented. This provides a meaningful boost to priming the Carbs in addition to the Fuel Column Pressure (Head). The Carb Fuel Pumps need all the help they can get, especially at low Fuel Tank levels.

P.S> The Square Nose Vent is a long Hose with a Small Plastic Bladder at the end. The Bladder has a Small Pinhole as an Air Intake.

So I must of grabbed this vent when I put in the GPR petcock/filter and redid the tank pickups

 

[mthomps]

If it runs ok without the valve somethings making up for the lack of the one way valve. Without the tank valve something has to provide the pressure to move fuel. It's super easy to get lost in the process when you start doing all the rad mods.

 

[Quinc]

I had a similar issue in my SJ and it ended up being when I jumped it water would splash on the plugs/wires and kill it. This was in surf/saltwater though.

 

[Storbeck]

If it runs ok without the valve somethings making up for the lack of the one way valve. Without the tank valve something has to provide the pressure to move fuel. It's super easy to get lost in the process when you start doing all the rad mods.

The fuel pump can do that, no?

The pressure in the fuel tank would be applied to both the supply and return lines equally, so it would not help pump the fuel to the carb. It would however contribute to the pressure pushing the needle open.

Venturing a bunch of guesses, @MTRHEAD probably set that pressure to be around 6 psi at WOT, and probably has to run pretty low popoff on those 50mm (?) carbs, so a few psi swing there could make a noticeable difference I would guess (lots of guessing here).

I REALLY don't want to sound like I'm arguing with MTRHEAD he's one of the guys that I would be asking questions and listening to what he says....I just have a hard time letting go of things that don't make sense to me.

Seems like the overall lesson that it's a good idea to spend a few bucks on a new valve is clear enough.

 

[MTRHEAD]

The fuel pump can do that, no?

The pressure in the fuel tank would be applied to both the supply and return lines equally, so it would not help pump the fuel to the carb. It would however contribute to the pressure pushing the needle open.

Venturing a bunch of guesses, @MTRHEAD probably set that pressure to be around 6 psi at WOT, and probably has to run pretty low popoff on those 50mm (?) carbs, so a few psi swing there could make a noticeable difference I would guess (lots of guessing here).

I REALLY don't want to sound like I'm arguing with MTRHEAD he's one of the guys that I would be asking questions and listening to what he says....I just have a hard time letting go of things that don't make sense to me.

Seems like the overall lesson that it's a good idea to spend a few bucks on a new valve is clear enough.

Hi.
yes 50mm carbs 80 return gives around 5psi at wot. want to test a 75 and 85 when it comes In. The fuel system is single pickup, All enlarged pickups, 1/4” lines to GPR petcock to GPR filter to Mikuni remote pump then individual 1/4” lines to carbs. I did single line because I like reserve where we ride and the GPR system can support upwards of 200hp So no need for dual pickups w/ no reserve for me

in 35 years of messing around I’ve never had a vent go bad.

note: i even tried the bad vent after correcting the issue with the new vent and the ski died in a NANO second when accelerating. Stopped opened the hood and changed back and happy riding!

 

[Sparkplug]

Put about 50 gallons on a waveblaster this yr with nothing even on the tank vent nipple

Engine does not need a check valve to run. The check valve is to relieve tank pressure.

I don't have a remote fuel pump on my main skis but a 650sx does and will run just fine without a tank vent also

 

[wmazz]

Hydrocarbons will cause the same problem as an exhaust leak.


Bill M.

 

[fastgtfairlane]

Put about 50 gallons on a waveblaster this yr with nothing even on the tank vent nipple

Engine does not need a check valve to run. The check valve is to relieve tank pressure.

I don't have a remote fuel pump on my main skis but a 650sx does and will run just fine without a tank vent also

Must've been pure luck that putting a one way valve on fixed their and my issue as well.

 

[Storbeck]

What would happen if a check valve failed so that it was always closed, and the fuel tank had no vent at all?

 

[wmazz]

Within approximately 5 to 15 minutes the engine will stall.
Problems will persist until the fuel tank is vented. Removing
the gas cap, will do the job until a vacuum inside the tank
reoccurs.

Bill M.