Fuel injection bybass fume problems?

Discussion in 'DIY Marinizing' started by crowsridge, Jan 15, 2011.

  1. crowsridge
    Joined: Apr 2010
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    crowsridge Senior Member

    I was curious about this. My big boat rebuild is on hold right now and am building a smaller jet sled. I was just wondering if having fuel injection gets rid of the fume/carb failure issues.

    Also, for example they say Honda outboards are the same block as their cars. Maybe an exaggeration? But maybe the donor car engine would accept a sealed starter etc from an outboard?

    Playing with a small inboard jet to run the boat.

    Ideas?

    Thanks, Chris
     
  2. gonzo
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    gonzo Senior Member

    Honda outboards share some parts with automotive engines. For example, pistons, rods and crankshaft. The blocks are completely different. What engine are you planning on converting to fuel injection and what system to install?
     
  3. crowsridge
    Joined: Apr 2010
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    crowsridge Senior Member

    I was facinated with these guys putting jet ski parts into small boats. While I dont want to go 65mph, I do like the jet advantage and it is much less than buying an outboard. I got a 1000cc donor jet ski yesterday for $100.00 Everything on it is great, but the engine. Lots of extra parts and a like new trailer to sell off. The original Rotax have bad reps anyway. I was looking for options to replace the Rotax into the new sled.

    I was marinizing diesels for the big boat and was thing the same for the jet. A gas engine is much less to buy than the TDI. Was just wondering if the injection would solve the fume issues? And if not, if there were options to sparkproof. I have a buddy at the salvage yard and had heard Honda parts were the same or similar.
     
  4. gonzo
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    gonzo Senior Member

    Rotax engines like all others for PWCs are high revving. The jets are direct drive and designed for that particular engine and application. You may make something else work, but at a higher cost than an outboard and less performance. If you have enough mechanical knowledge to re-engineer and fabricate all that, rebuilding an outboard will be a fraction of the cost.
     
  5. crowsridge
    Joined: Apr 2010
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    crowsridge Senior Member

    Hmm? Not sure about that, here at least. The cheapest OB 100 hp I have found is about 3K for an old 2 stroke. Then rebuld and buy a pump. The pumps on an outboard are even worse for performance than the inline type and an extra cost. I can get a rebuilt Rotax for $1200.

    Was looking for options to turn the pump besides another Rotax.
     
  6. Steve H
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    Steve H Senior Member

    I don't think you can find a small automotive engine that will turn the needed rpm's to make that jet perform the way it was designed to.
     
  7. crowsridge
    Joined: Apr 2010
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    crowsridge Senior Member

    What about this? The machinist said do a reverse reduction gearbox. For simplicity sake. A Mercruiser engine I can get does 3500rpms. The jetski does 7000. A 3" hear on the motor and a 6" on the JS shaft. Seems a bit too easy.
     
  8. CDK
    Joined: Aug 2007
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    CDK retired engineer

    It is easy, just like it seems.
    But the gearbox must be an industrial one with nothing in it besides 2 gears and a few bearings. A marine gearbox with cone clutches inside is not suitable for this purpose. And do not forget that the direction of rotation changes!
     
  9. MechaNik
    Joined: Jan 2011
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    MechaNik Senior Member

    Would the jet still be ok for a much slower heavier vessel? Wouldn't you want a more generous inlet and larger outlet which you may be able to tweak. Otherwise you may find excessive cavitation and less than ideal performance.
     
  10. crowsridge
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    crowsridge Senior Member

    I was thinking of using the stich and glue 400 lb. version for the jet ski pump and the Berkeley pump in the heavier 20' version. of the sled. The Berkeley turns clockwise looking at the shaft. going to have to think a out the rotation issue.
     
  11. gonzo
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    gonzo Senior Member

    A rebuilt rotax is about the same price as a rebuilt powerhead for an outboard. If you are looking at savings, this is not a good plan.
     

  12. crowsridge
    Joined: Apr 2010
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    crowsridge Senior Member

    Saving are good, but not foremost. I dont need an outboard powerhead for this though. Powering the boat with something quieter than a screaming 2 stroke at 7K would be better. Diesel has its own reasons for being and has the cool factor too. Having it run at 3500-3800 turning the pump at 7K seems like a decent plan. I really want to learn more about Lauries setup. So I know it can be done, just need to do the planning right.
     
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