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  1. #1
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    Help with an Mercury 150 2.5 Carbed to EFI 175 conversion

    So long story short I blew a powerhead on my 1998 Merc XRI 150. I traded it in on a rebuilt XR6 150 but soon started having issues with it. The guy I bought it from offered to swap me back my original motor the 98 XRI but he had removed the EFI parts and put on carbs. So I went ahead and did it. So the motor I currently have is a 1998 XRI 150 serial number 0D275859 with carbs from a mid 90's XR6 and NO oil injection. I am not happy with the power from this current setup 52 MPH at 5500 RPMs, same motor before I blew it was hitting 60 MPH at 5800 RPMs the XR6 was even better hitting 62mph at 6000 RPMs. Everything has stayed the same lower unit, prop motor height all the same yet the rebuild with carbs just doenst have the power.
    The guy I bought the rebuild from said it might be do to the carbs not matching the block and heads right. They are model WHM 14a
    So in my quest to get my speed back I came across a buddy who blew is his 1998 merc 175 EFI motor that will sell it to me at $600, I need a lower unit any how so I thought this might be a good opportunity to get my power back.
    I am considering trying to convert my motor back to EFI buy using his motor as a donor but realize his motor blew for a reason so I dont know if this is all worth it and how hard the work would be? I would like to add the oil injection back too but not sure how much of his oil injection I can use or have tested to make sure its good before I go this route. I can send the injectors off for testing\cleaning but I am not sure how much trouble this is going to be? I dont expect to get 175 HP but just get back to where I was before would be great.

    My other option is to try another set of carbs to see if that improves my power.

    Any help or options will be greatly appreciated

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  3. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #2
    0D275859 was built in 1993.
    What was done in the powerhead?
    Where are the ORIGINAL EFI components?


    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
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    #3
    So I guess I have a 1993 then? The original powerhead was bored, had 6 new pistons, rings and the works. He used the intake, reeds, carbs, ect off of a early 90's 150 XR6. The original EFI components were likely sold. The guy who rebuilt it said he doesn't like reusing the old EFI components so he just uses carbs but I never expected to loose this much top end. I am guessing that the conversion back to EFI isnt going to be worth all the trouble?

  5. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #4
    If you had the complete electrical and fuel system to "donate", it could be done. However... the ECU would be providing too much fuel for a 150 Powerhead (the cylinder blocks ARE different between the 150 and the 175).


    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
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    #5
    Hi Don what is different in the block? I assumed it would just be the heads. Would I be better of just trying new carbs? I am running wmh 14a on there now.

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    #6
    Quote Originally Posted by Gsmith223 View Post
    Hi Don what is different in the block? I assumed it would just be the heads. Would I be better of just trying new carbs? I am running wmh 14a on there now.
    Blocks are same, port timing in the sleeves are different. 175 ecu would be a little fat on a 150.
    Only difference in efi for those is fuel curve in ecu. Get the right ecu or have someone put a 150 curve in it.

  8. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #7
    The block castings are the same (except for the cast numbers). Cylinder sleeve porting is different in the 150, 175, and 200 (even the EFI engines). Separate part number for each cylinder block (based on HP rating).

    I believe that's what 90_5.0 was saying, too.

    Agree... use correct ECU or calibration for best results (matching the actual powerhead used).


    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
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  9. Member silverbullet02's Avatar
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    #8
    You can use the 175 donor motor for everything, even use the 175 ecu temporarily until you can find a 150 ecu. It'll be a little rich and run ok and get you on the water, but if the price is right, it'll get you down the path of going back to efi. I'd leave the oil injection off tho if it were me.


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