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Thread: 1984 SurfJet!

  1. #11
    PWCToday.com Is My Home Away From Home delagem's Avatar
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    Re: 1984 SurfJet!

    The exhaust ports on a SurfJet measure out at 166degrees of duration, down in lawnmower territory. Raising the exhaust port by 1.0mm increases the duration to 172deg, a little closer to optimal. Something in the 170 to 180 deg should be a good spot for this motor, but due to the poor exhaust design, I’m trying to go in small increments, and not go too far.

    Surprisingly, the transfers are fairly close to where we would like to see them, at 131 deg.



    The stock exhaust port:



    The exhaust port raised 1.0 mm, and polished:

    Attached Images Attached Images
    Last edited by delagem; 04-24-2011 at 10:30 PM.
    '58 Vincent Amanda Water Scooter, 0rpm, 0mph

    '84 SurfJet 236ss Freestyle, 5950rpm, 24.6 mph

    '91 Jetmate! SX-R 800,GroupK carbs,R&D 26cc head,R&D ProLok F/A, Coffman Rocket Pipe,Impros 13-20,76mm nozzle: 6630rpm and 38.1mph GPS

    '92 SL650/750, dry pipe,extended pump,trim,HotSeat Waterbox: 6320rpm, 50.1 mph

    '00 SLX,Tau Ceti F/A's,NuJet prop: 6670rpm, 63.1 mph

    '03 Octane, Watcon 2318 CDI

    '04 MSX140,Impros stage 2 Powertune 14/23,WetWolf,6deg wedge: 6750rpm, 60.5 mph

  2. #12
    PWCToday Guru MattK1's Avatar
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    Re: 1984 SurfJet!

    Great thread, thanks for posting!!

  3. #13
    PWCToday.com Is My Home Away From Home delagem's Avatar
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    Re: 1984 SurfJet!

    There are supposedly some gains to be had by polishing the pump, shimming the impeller, and sealing the nozzle properly. I don't doubt it, but I expect the gains are small. The biggest gain would likely be the shimming of the impeller. I used a Mother's Powerball Mini, chucked up in a drill press, with red rouge polish, for the initial work on the pump and cover. Then, I switched to a Foredom Grinder (a commercial porting tool, like a Dremel only 1/3 horsepower) to do the final polish.





    Attached Images Attached Images
    Last edited by delagem; 04-24-2011 at 10:40 PM.
    '58 Vincent Amanda Water Scooter, 0rpm, 0mph

    '84 SurfJet 236ss Freestyle, 5950rpm, 24.6 mph

    '91 Jetmate! SX-R 800,GroupK carbs,R&D 26cc head,R&D ProLok F/A, Coffman Rocket Pipe,Impros 13-20,76mm nozzle: 6630rpm and 38.1mph GPS

    '92 SL650/750, dry pipe,extended pump,trim,HotSeat Waterbox: 6320rpm, 50.1 mph

    '00 SLX,Tau Ceti F/A's,NuJet prop: 6670rpm, 63.1 mph

    '03 Octane, Watcon 2318 CDI

    '04 MSX140,Impros stage 2 Powertune 14/23,WetWolf,6deg wedge: 6750rpm, 60.5 mph

  4. #14
    PWCToday.com Is My Home Away From Home delagem's Avatar
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    Re: 1984 SurfJet!

    The available shims are .010Ē, .030Ē, and .045Ē

    I like to work in mm, so those are: .25mm, .75mm, and 1.14mm

    Upon disassembly I found my SurfJet to contain 3 shims under the impeller.
    1 ea .25 mm
    2 ea .75 mm



    Upon reassembly with an aftermarket aluminum impeller, those 3 shims made the new impeller too tight to turn. I removed first the thin shim then swapped the thin for a thick, and finally found that combination to work. Here is my final combination
    1 ea .25 mm
    1 ea .75 mm

    Impeller clearance is now .330mm or .013Ē. This was the closest I could get it with the shims available. An additional .25mm should make this perfect, as tight as possible without rubbing.

    Make sure you torque the impeller down very well! If you donít, youíll find your impeller spinning itself off the shaft the first time you chop the throttle, and youíll have to polish your pump all over again from the gougesÖ.
    '58 Vincent Amanda Water Scooter, 0rpm, 0mph

    '84 SurfJet 236ss Freestyle, 5950rpm, 24.6 mph

    '91 Jetmate! SX-R 800,GroupK carbs,R&D 26cc head,R&D ProLok F/A, Coffman Rocket Pipe,Impros 13-20,76mm nozzle: 6630rpm and 38.1mph GPS

    '92 SL650/750, dry pipe,extended pump,trim,HotSeat Waterbox: 6320rpm, 50.1 mph

    '00 SLX,Tau Ceti F/A's,NuJet prop: 6670rpm, 63.1 mph

    '03 Octane, Watcon 2318 CDI

    '04 MSX140,Impros stage 2 Powertune 14/23,WetWolf,6deg wedge: 6750rpm, 60.5 mph

  5. #15
    PWCToday.com Is My Home Away From Home delagem's Avatar
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    Re: 1984 SurfJet!

    These Fuji engines are known for too-tight piston pins, just like on the older Polaris models. I ran a 14mm ball or flex hone thru the piston bosses so that the piston pin can be inserted without force. Don’t do too much, about 10 seconds using a cordless drill is all it took for mine. You don’t want the pin to fall through; rather, you should be able to push it into place with just your thumb.

    Attached Images Attached Images
    Last edited by delagem; 04-24-2011 at 10:44 PM.
    '58 Vincent Amanda Water Scooter, 0rpm, 0mph

    '84 SurfJet 236ss Freestyle, 5950rpm, 24.6 mph

    '91 Jetmate! SX-R 800,GroupK carbs,R&D 26cc head,R&D ProLok F/A, Coffman Rocket Pipe,Impros 13-20,76mm nozzle: 6630rpm and 38.1mph GPS

    '92 SL650/750, dry pipe,extended pump,trim,HotSeat Waterbox: 6320rpm, 50.1 mph

    '00 SLX,Tau Ceti F/A's,NuJet prop: 6670rpm, 63.1 mph

    '03 Octane, Watcon 2318 CDI

    '04 MSX140,Impros stage 2 Powertune 14/23,WetWolf,6deg wedge: 6750rpm, 60.5 mph

  6. #16
    PWCToday.com Is My Home Away From Home delagem's Avatar
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    Re: 1984 SurfJet!

    Apparently the Mikuni BV22 carburetor that was stock on the SurfJet was discontinued a long time ago. But thatís ok, it was too small anyways. Using the formula in Gordon Jenningís 2 Stroke Tunerís Handbook, we see that:

    Dia = k x square root of (C x N)

    Where C is the displacement in liters, N = target RPM peak, and k is a constant, varying based on the application. Motocross motors run .8, and roadrace is .8 to .9 for a constant. I used .8, .1275 (for 127.5cc), and a target of 7,000 rpm. This yields 23.9mm, the optimal carburetor bore for our application. Donít view this as the law, itís just a starting point. We will still need to test larger and smaller carburetors.

    I understand there is a Walbro carburetor of some variety that is a performance upgrade for the SurfJet. I have been unable to determine the model of that carb. If anyone knows, I will update this page.

    Walbro themselves recommended to me a WB-45. This is a 30mm bore carb. But as you can see, it wonít be a direct swap. I may try this one, if no better alternatives turn up. It is a good carb, a true watercraft design. It will run upside down, and wonít allow fuel to spill when inverted. The specifications of the Walbro WB-45 are shown below:

    A bit of searching led me to the Mikuni BV24, the stock carb on the 1988 EZGO Golf Cart. The cart uses the throttle in a default open position, so it was necessary to flip the spring around to effect a normally closed setting. I also had to pull the choke line, and install a primer fitting into the hole left from the choke shaft.

    The mounting flange on the carburetor did require a bit of grinding to open up the bolt holes for the slightly narrower spacing.
    Attached Images Attached Images
    Last edited by delagem; 04-24-2011 at 11:07 PM.
    '58 Vincent Amanda Water Scooter, 0rpm, 0mph

    '84 SurfJet 236ss Freestyle, 5950rpm, 24.6 mph

    '91 Jetmate! SX-R 800,GroupK carbs,R&D 26cc head,R&D ProLok F/A, Coffman Rocket Pipe,Impros 13-20,76mm nozzle: 6630rpm and 38.1mph GPS

    '92 SL650/750, dry pipe,extended pump,trim,HotSeat Waterbox: 6320rpm, 50.1 mph

    '00 SLX,Tau Ceti F/A's,NuJet prop: 6670rpm, 63.1 mph

    '03 Octane, Watcon 2318 CDI

    '04 MSX140,Impros stage 2 Powertune 14/23,WetWolf,6deg wedge: 6750rpm, 60.5 mph

  7. #17
    PWCToday.com Is My Home Away From Home delagem's Avatar
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    Re: 1984 SurfJet!

    The stock reeds for the SurfJet are the standard stainless steel variety that were found on motocross 2 strokes in the 1970’s and 80’s from Japan. A phenolic or carbon fiber reed is definitely going to breathe better. It will also do much less damage when, as all reeds eventually do, it snaps off and sends a piece through the motor.

    I showed this reed block to a well-known engine builder, Tony Doukas of TDR Racing. He suggested opening the reed windows up, leaving about 1.5 to 2.0mm bars in place of the nearly 10mm bars on the current piece. He also makes performance reeds for this machine, you can contact his company to order them at www.bansheedepot.com or search for TDR Tony Doukas Racing. They are located in Punta Gorda, FL. I also have a few extra pair in stock, if Tony is unable or unwilling to make just a single pair.

    Another option is the Boyesen 2 piece Power Reeds, part number 423, stock for a Suzuki DT8, DT9.9, and DT15 2 stroke outboard motors.

    TDR's reeds were $20 a set. The Boyesens were $87! While I am intrigued by the design of the Boyesen, I question whether they are actually any better performing than the TDR's, at 4x the price.

    Last edited by delagem; 04-24-2011 at 11:11 PM.
    '58 Vincent Amanda Water Scooter, 0rpm, 0mph

    '84 SurfJet 236ss Freestyle, 5950rpm, 24.6 mph

    '91 Jetmate! SX-R 800,GroupK carbs,R&D 26cc head,R&D ProLok F/A, Coffman Rocket Pipe,Impros 13-20,76mm nozzle: 6630rpm and 38.1mph GPS

    '92 SL650/750, dry pipe,extended pump,trim,HotSeat Waterbox: 6320rpm, 50.1 mph

    '00 SLX,Tau Ceti F/A's,NuJet prop: 6670rpm, 63.1 mph

    '03 Octane, Watcon 2318 CDI

    '04 MSX140,Impros stage 2 Powertune 14/23,WetWolf,6deg wedge: 6750rpm, 60.5 mph

  8. #18
    PWCToday.com Is My Home Away From Home delagem's Avatar
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    Re: 1984 SurfJet!

    IGNITION

    My unit has a Japanese made Kokusan CDI/Coil assembly. My experience with Kokusan ignitions in motorcycles has been somewhat problematic, but this unit seems to be fairly reliable.

    I have been unable to determine if there is a rev limiter or not on this unit, but repeated attempts to over-rev it with a PET2100 tachometer connected have shown that the motor will not rev past 10,000 rpm, even with no load on the pump (out of the water).

    This is good for 2 reasons; first, we donít need to determine how to eliminate the rev limiter if it were to, say, stop the fun at 6,000 rpm. My target for this machine all along has been 7,000 rpm and 30mph. The rev limiter wonít cause us problems for that.

    Second, rpm limits should be determined by piston speed. According to Jennings book, motors can live for a short time at nearly 4,000 feet/minute piston speed, but for absolute reliability they need to stay below 3,500 feet/minute. 10,700rpm equates to this 3,500 feet/minute piston speed for this motor.
    '58 Vincent Amanda Water Scooter, 0rpm, 0mph

    '84 SurfJet 236ss Freestyle, 5950rpm, 24.6 mph

    '91 Jetmate! SX-R 800,GroupK carbs,R&D 26cc head,R&D ProLok F/A, Coffman Rocket Pipe,Impros 13-20,76mm nozzle: 6630rpm and 38.1mph GPS

    '92 SL650/750, dry pipe,extended pump,trim,HotSeat Waterbox: 6320rpm, 50.1 mph

    '00 SLX,Tau Ceti F/A's,NuJet prop: 6670rpm, 63.1 mph

    '03 Octane, Watcon 2318 CDI

    '04 MSX140,Impros stage 2 Powertune 14/23,WetWolf,6deg wedge: 6750rpm, 60.5 mph

  9. #19
    PWCToday.com Is My Home Away From Home delagem's Avatar
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    Re: 1984 SurfJet!

    The exhaust is a problem. There's just no room for a proper exhaust. There is a small, 1" dia pipe, about 5" long, inside the pump cavity, for an exhaust. That's it. No expansion chamber, nothing.



    The bigger problem comes when we try to calculate the correct exhaust for my hypothetical 30 mph, 7,000 rpm turning beast....

    L = E x V / N

    Where
    L is the length in inches from the exhaust port to the midpoint on the reflecting cone in the expansion chamber.
    E is the exhaust open period, in degrees
    V is the wave speed, in feet per second
    N is crankshaft speed, in rpm

    Using some basic numbers of
    E 170
    V 1,700
    N 7,000

    We find that L = 43.7 inches. Now where exactly do we fit a 44" exhaust onto this thing?
    Attached Images Attached Images
    Last edited by delagem; 04-24-2011 at 11:37 PM.
    '58 Vincent Amanda Water Scooter, 0rpm, 0mph

    '84 SurfJet 236ss Freestyle, 5950rpm, 24.6 mph

    '91 Jetmate! SX-R 800,GroupK carbs,R&D 26cc head,R&D ProLok F/A, Coffman Rocket Pipe,Impros 13-20,76mm nozzle: 6630rpm and 38.1mph GPS

    '92 SL650/750, dry pipe,extended pump,trim,HotSeat Waterbox: 6320rpm, 50.1 mph

    '00 SLX,Tau Ceti F/A's,NuJet prop: 6670rpm, 63.1 mph

    '03 Octane, Watcon 2318 CDI

    '04 MSX140,Impros stage 2 Powertune 14/23,WetWolf,6deg wedge: 6750rpm, 60.5 mph

  10. #20
    PWCToday.com Is My Home Away From Home delagem's Avatar
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    Re: 1984 SurfJet!

    You can buy a service manual, and a parts manual for these machines over at www.deckjetwatercraft.com. However, there are a few problems....

    DISCREPANCIES IN SERVICE MANUAL/PARTS MANUAL

    The Service Manual shows 2 bearings of 6304C3, and one 6205C3. However, the actual bearngs are all 6205C3. Stock bearings had a locating pin, the replacement bearings youíll find wonít have that. Just use a small amount of the case sealant in the bearing recess in the case, to ensure the bearing is held in place and canít ďspinĒ in the case.

    The little hose the runs up the side of the exterior of the motor isnít addressed anywhere in the Service manual. View 1 shows it, Drawing Item 42, but doesnít mention that thereís a check valve in there. Make sure the check valve is clear. The valve should be aligned to allow flow upwards. This hose allows fuel/oil mix to travel from the lower cylinder intake tract, up to a direct feed onto the upper crank bearing.
    '58 Vincent Amanda Water Scooter, 0rpm, 0mph

    '84 SurfJet 236ss Freestyle, 5950rpm, 24.6 mph

    '91 Jetmate! SX-R 800,GroupK carbs,R&D 26cc head,R&D ProLok F/A, Coffman Rocket Pipe,Impros 13-20,76mm nozzle: 6630rpm and 38.1mph GPS

    '92 SL650/750, dry pipe,extended pump,trim,HotSeat Waterbox: 6320rpm, 50.1 mph

    '00 SLX,Tau Ceti F/A's,NuJet prop: 6670rpm, 63.1 mph

    '03 Octane, Watcon 2318 CDI

    '04 MSX140,Impros stage 2 Powertune 14/23,WetWolf,6deg wedge: 6750rpm, 60.5 mph

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