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Thread: Help! Jet, impeller, sleeve questions

  1. #1

    Default Help! Jet, impeller, sleeve questions

    Alright so I have an old mercury 140hp outboard (inline 6) with a jet. From idle to about half throttle everything works normally. After half throttle the engine will rev up quickly without an increase in thrust. In my opinion this is caused by one (or more) of the following:
    1. Sleeve has grooves
    2. Improper clearance - needs shimmed
    3. Incorrect impeller size and/or pitch
    - Is there another possible cause?

    Now 1 and 2 I can handle, but 3 is what I need help on. How do you tell what size and pitch you need? Whats the proper method for measuring the impellers I already have? How do you measure diameter, and how do you measure pitch?

    And finally, can anyone recommend shops in the valley that would carry sleeves, impellers, shear keys, etc at a decent price? Anchorage as well I suppose.

  2. #2
    Moderator AKmud's Avatar
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    www.outboardjets.com - for troubleshooting issues

    Greatland welding (on the Palmer/Wasilla hwy) has lots of jet parts. J Kimberly in Anchorage if Gary can't help you out at Greatland.
    AKmud
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    The porcupine is a peacful animal yet God still thought it necessary to give him quills....

  3. #3

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    Check your reverse bucket, make sure itís in the full forward position, sometimes the linkage gets loose and it will move in the neutral position.

    Check impeller to see if dinged and put an edge back on if aluminum.

    How do you measure diameter, and how do you measure pitch?
    Diameter will be stamped on impeller. You can not change the pitch on an outboard jet.

  4. #4
    Member Dirtofak's Avatar
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    Has this motor/jet combination worked previously on the same boat, same setup?

    Revving quickly without an increase in thrust smells like cavatation to me. Make sure the grate is clear. Is the RPM the same when it does it when the boat is loaded differently or in a corner?

    Performance Marine in Anchorage for jet parts.

  5. #5

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    Thanks for the responses guys. Yeah, the inpeller has some dings, and the sleeve is pretty much shot. I just find it hard to believe a few grooves in the sleeve could be responsible for these symptoms, but hey what do I know

    So before I go buy a sleeve and impeller, is there a way to determine what size I need? I suppose I could just buy the same size as I have now, and hope this is the correct size.

  6. #6

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    Quote Originally Posted by onstep View Post
    You can not change the pitch on an outboard jet.
    Apparently that isn't true. From what I'm reading you match pitch to the HP of the outboard so it operates at its proper RPM. I'm not saying you can mix and match pitches for a given HP, I'm saying a given HP needs a specific pitch.

    Whether I have the wrong pitch, or a different problem remains to be seen I suppose.

  7. #7
    Moderator AKmud's Avatar
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    If the sleeve is shot and the impeller is roughed up you may be experiencing cavitation within the jet unit at the higher RPM (water blowing back down past the impeller). Is there room to shim it closer to the sleeve? There should be 7 shims (washers) on the drive shaft at all times. Make sure there is some combination of 7 above + below the impeller. If you still have a few shims on top, change them around and try to get a little more life out of it.

    Worst case, put a new sleeve in it and go with a new (preferably stainless) impeller. If it still doesn't perform, you have other troubles.
    AKmud
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    The porcupine is a peacful animal yet God still thought it necessary to give him quills....

  8. #8

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    4. Can we change jet impeller pitch for load or speed?

    No. Unlike a propeller drive, a jet can develop full HP at a standstill. We choose an impeller that gives rated factory RPM at full throttle. RPM hardly varies between a heavy load and running fast with a light load.

    11. Can impeller pitch be changed for more speed or heavier loads?

    No. Unlike propellers, an outboard jet drive at full throttle will turn up to rated RPM even tied to a dock. It is not possible to use a lower pitch for load carrying and a higher pitch for speed. The impeller pitch is chosen to provide rated RPM at full throttle regardless of the weight in the boat.


    14. Does a stainless steel impeller improve performance of a jet drive?

    Stainless steel impellers work well on motors above 100 HP. They give less slippage on start up and therefore can pickup a heavier load. Top speed of, maybe, one to two mph or better. Below 100 HP, the main advantage is longer wear life.



  9. #9

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    onstep I think you missed my point again, but it's all good. I emailed Specialty Mfg. Company and hopefully they will be able to tell me the correct size and pitch for my engine. I have zero problems with replacing my sleeve and impeller, I just want to make sure I'm putting the correct size and pitch in.

  10. #10

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    Have you pulled it out to see what size you have?

  11. #11

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    The impeller that I have in there doesn't say, but I have another one that looks the same that is stamped 7 3/8 so I'm guessing they are the same size. But that size may be too small. See, I bought this jet last summer after my 80hp merc gave up the ghost. This particular setup hasn't really ever performed as it should, but for the price I paid I'm not complaining. THe engine is strong, there is just a misconfiguration with the jet. So I need to know what *should* be in there, regardless of what is actually in there. Hopefully this company emails me back.

  12. #12
    Member Dirtofak's Avatar
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    Call Performance Marine in Anchorage. My 115 uses a 7 3/8. I believe that you should have a 7 5/8. THey have a few used ones. Maybe you can trade if need be.

  13. #13

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    Check to see if you have a serial number located where the reverse gate attaches to the jet pump. It will probably be a four to 7 digit number.

    There should also be a model number. This is on the other side of the jet, where the reverse gate attaches as well.

  14. #14
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    Default Jet performance

    If everything's operating correctly & once RPMs reach a certain point the engine quickly revs up, my bet is as someone posted earlier...cavitation. Even with a worn impellor or one with the wrong pitch (btw, there's only two pitches available for impellors & it should be stamped on yours...either v4 or v6. The final tuning for impellors to match HP is to have the trailing edge of the impellor machined off) If you've changed engines out, have you checked the hight of your jet foot in relation to the bottom of your transom? Very likely, it's not the RPM being reached, but the fact of your boat coming up on step in combination with your foot being too high = instant cavitation = revving with no thrust. It only takes being a 1/4" too high.

    Even with worn impellor / sleeve, what you would experience is reduced performance across the RPM range, not a sudden surge in RPMs. The 7 3/8 impellor is the correct one for your 140, most likely a v4 pitch, or a trimmed-back v6.

    Brian

  15. #15

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    Thanks for the info guys

    I'm fairly sure the foot height is correct, and I'm also fairly sure this problem isn't related. When I first purchased this, the foot sat really low - probably 4 inches under my boat. I took it for a quick spin and it did this. Later I adjusted the transom so the leading edge of the foot is right there at the bottom of the boat, maybe 1/4" under, and it still does it. If memory serves me, I swapped the boot and impeller from my 80 onto it and it still did it, but don't quote me on that.

    Maybe if I can get my camera working I'll take various pictures of it today and you guys could have a look and take some educated guesses? This one really has me stumped.

  16. #16
    Member AKBassking's Avatar
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    I had a similar problem and it was my reverse gate. Take off the reverse gate (be careful you have a clear path in front of you) and take it to full throttle. At lease that will eliminate this possible cause. Also check the impeller key to may sure it isn't bad, along with the other suggestions listed here.

    It could be a combination of all the stuff listed here on this thread.

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  17. #17

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    Well I pulled the boot off to take a look at what was going on. First thing I saw made my jaw drop: The bolts that hold the sleeve in were no longer doing their job! The sleeve could float up and down about 1/4"! I'm not sure if that is responsible for these particular symptoms or not, but it certainly isn't good. I've put a different boot, sleeve, and impeller on. Hopefully I can get out somewhere to test it out soon. Will update as I figure this out.

  18. #18

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    Finger lake is open

  19. #19

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    Thanks for the info, but the Little Su is closer to me. I'll go upstream just in case

  20. #20
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    Were the bolts holding the sleeve loose or broken off?
    Tennessee

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