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  1. #1
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    225 Promax offshore trim issue

    I have a 225 promax with an offshore mid. It's a mercury racing pump. Serial number is 004512.

    I've been having a slow trim issue but it only struggles going up when past the half way point.
    I'll give you a scenario. Let's say the engine is trimmed all the way down. I'll start trimming up and it works fine. Then once it gets a little above halfway, it slows down. Then it struggles so bad that it won't even trim anymore. The trim motor will be running and the engine will barely be going up. It get's going so slow that it looks like it's hardly moving.

    I think it's either the motor is bad or it needs primed.

    I just replaced the reservoir cap because it was cracked. Also, it used to screech/ squeak when I would let off the trim. I assumed it did that since it sat in storage for a while. After I used it more, it quit squeaking.

  2. #2
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    Click image for larger version. 

Name:	IMG_3044.jpg 
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ID:	468479
    This is my trim pump.
    Last edited by simpson_3; 06-28-2020 at 11:22 AM.

  3. #3
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    Does the pump sound like it is slowing down/changing pitch when the trim slows down? Any "bubbly" noise? The pump could be cavitating. I suppose you also could have a bent trim cylinder and the pump is hitting the relief pressure and bypassing the cylinder.

    To address your one point, these pumps are self priming since they are a gear pump with a reservoir where the air pockets can return back to tank. Typically this is done just by trimming from full down to full up and back several times.

  4. #4
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    Trim Pump Struggles

    Quote Originally Posted by simpson_3 View Post
    I have a 225 promax with an offshore mid. It's a mercury racing pump. Serial number is 004512.

    I've been having a slow trim issue but it only struggles going up when past the half way point.
    I'll give you a scenario. Let's say the engine is trimmed all the way down. I'll start trimming up and it works fine. Then once it gets a little above halfway, it slows down. Then it struggles so bad that it won't even trim anymore. The trim motor will be running and the engine will barely be going up. It get's going so slow that it looks like it's hardly moving.

    I think it's either the motor is bad or it needs primed.

    I just replaced the reservoir cap because it was cracked. Also, it used to screech/ squeak when I would let off the trim. I assumed it did that since it sat in storage for a while. After I used it more, it quit squeaking.
    Could be debris or sludge in the lines? Try changing out the trim oil. Make sure the cap has a tiny vent hole in it. If it doesn't vent you'll get an airlock stall. When racing, I never bothered to use SAE 20W and used hydraulic jack oil instead (purpose blend for jacks, hydraulic rams, tractors, etc). Sounds to me like the pump is starved for an oil supply?

  5. #5
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    Quote Originally Posted by JCSmile View Post
    Does the pump sound like it is slowing down/changing pitch when the trim slows down? Any "bubbly" noise? The pump could be cavitating. I suppose you also could have a bent trim cylinder and the pump is hitting the relief pressure and bypassing the cylinder.

    To address your one point, these pumps are self priming since they are a gear pump with a reservoir where the air pockets can return back to tank. Typically this is done just by trimming from full down to full up and back several times.
    I have your phone number. Do you want me to text you a video of it? I talked to you at the Cassville rally last year.

  6. #6
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    Quote Originally Posted by WaterZebra View Post
    Could be debris or sludge in the lines? Try changing out the trim oil. Make sure the cap has a tiny vent hole in it. If it doesn't vent you'll get an airlock stall. When racing, I never bothered to use SAE 20W and used hydraulic jack oil instead (purpose blend for jacks, hydraulic rams, tractors, etc). Sounds to me like the pump is starved for an oil supply?
    I thought that to but I don't get why it trims down fine. Is there a valve for the up side that could be messed up?

  7. #7
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    Trim Reservoir

    Quote Originally Posted by simpson_3 View Post
    I thought that to but I don't get why it trims down fine. Is there a valve for the up side that could be messed up?
    Per your photo, you can see the fluid level in the reservoir. When you trim in, fluid is pumped back IN to the tank. When you trim OUT the fluid level should drop. Try running the trim without the cap on. If the level doesn't drop at some point trimming out then the valve body should be disassembled, cleaned and inspected. It could be be debris fouling up a spring loaded ball valve seat. I'm betting you have a misrun cap with no venting.

  8. #8
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    Quote Originally Posted by WaterZebra View Post
    Per your photo, you can see the fluid level in the reservoir. When you trim in, fluid is pumped back IN to the tank. When you trim OUT the fluid level should drop. Try running the trim without the cap on. If the level doesn't drop at some point trimming out then the valve body should be disassembled, cleaned and inspected. It could be be debris fouling up a spring loaded ball valve seat. I'm betting you have a misrun cap with no venting.
    I've ran it with the cap off and it doesn't make a difference. Where is the the spring loaded valve seat at?

  9. #9
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    Valve Access

    Quote Originally Posted by simpson_3 View Post
    I've ran it with the cap off and it doesn't make a difference. Where is the the spring loaded valve seat at?
    The large grey bolt heads on the sides (photo)

  10. #10
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  11. #11
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    Quote Originally Posted by WaterZebra View Post
    The large grey bolt heads on the sides (photo)
    If I undo those bolts is there going to be a lot of oil pressure?

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    Trim Rework

    Quote Originally Posted by simpson_3 View Post
    If I undo those bolts is there going to be a lot of oil pressure?
    Loosen the line connections too to bleed off any residual pressure.

  13. #13
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    Quote Originally Posted by WaterZebra View Post
    Loosen the line connections too to bleed off any residual pressure.
    I'm going to order a new bob's pump. Are my current fittings compatible with the bobs pump?

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