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  1. #1
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    03 Merc 2.5 questions

    Hi everyone.
    I have a 1977 Cobra Phantom that I am doing an engine swap on (along with paint and carpet). I put some pics on my profile of the boat, it is a pretty light boat and was a rocket with the 1500 on it compared to the other boats I have owned.
    I am replacing a 74 Mercury 1500 with a carburated 2003 Mercury 2.5L 200 HP (OT444387). I bought the engine disassembled from a local boat shop. It has all new internals still in their boxes and I have to assemble it.
    My questions are:
    1) Should I opt for the Boyesen or other aftermarket dual stage reed?

    2) Are there any tips/tricks for tuning or mods I can do prior to or during assembly that I may benefit from in a performance or reliability stand point?

    3) Aftermarket intake/carb assemblies that may bring this thing alive?

    4) I have seen several similar engines with hoses that were yellow or blue, is there a reason to change these other than cosmetic (sorry I can't say exactly what the hoses are called but they appear to join all the crankcase areas to maintain a balanced pressure between them....totally guessing on that one


    Thanks for any help, comments. I am hoping to learn as much as I can with this new toy.


    Slimm

  2. #2
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    Aw c'mon now I know someone has something to say about this thing even if it is just how nice the color is or how pretty the sound is.

  3. #3
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    1. I'd go with the Carson reeds over Boyesens.

    2. New rod bolts. Any other internal mods are all going to depend on how fast you want to go and if you want to have a little more machining done. The 200 will go pretty fast unmolested.

    3. There is nothing "aftermarket" unless you get into injection.

    4. They look different.

  4. #4
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    Bring the heads down to 34 or 35 CC Set timing @ 25 and run good fuel and oil.If it has the old gear drive oil pump,Block it off and premix.Carson reeds.

  5. #5
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    Quote Originally Posted by outasite View Post
    Bring the heads down to 34 or 35 CC Set timing @ 25 and run good fuel and oil.If it has the old gear drive oil pump,Block it off and premix.Carson reeds.

    he's got an O ring head motor. There are certainly people to mill the heads but its going to be more of a chore and expense. Then theres the whole problem of the rev limiter. If it was mine I'd have the block deck milled, use old heads with gaskets and go back to the old style switch boxes and coils. 5700 or whatever those max out would drive me crazy.

  6. #6
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    You're going from a '74 Mercury 1500 to a 2003 Mercury 2.5L 200 HP on a light boat! I know I'll get alot of flac for saying this...
    but I would learn to drive the boat/engine in stock form first before adding more to it. You already have more weight and almost
    twice the horse! Your ride is gonna be quite different!


  7. #7
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    It's not much more weight and he never said he couldnt handle what he had now. I know the published numbers always put the inline at or around 300 lbs but that never includes the trim cylinders and pump. By the time its all together Its a good 350 lbs. So its about 75 lbs different or the same as one skinny kid sitting in back.

    As someone who went from a Johnson 90 to a 260 Merc in a similar sized boat, I can relate. It works out just fine. Just upgrade the steering and drive that sucker hard.

  8. #8
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    WooHoo now we are getting somewhere. Thanks for the suggestion kingsbiship and I have put a good bit of thought into learning to drive the boat with the new power safely. I am installing SeaStar PRO hydraulic steering, get that safety concern outta the way first. I have driven race cars on asphalt and dirt and lots of 4x4's so my learning curve is a bit faster than the average guy who buys a fast boat and hammers down all carefree and careless, but fast boats are new to me and keep me on my toes every time I head out.

    Wired, is there a place I can learn what old heads will fit my block and what other changes I might have to make to compensate if I switch to the older heads and to get some part numbers for switchboxes and coils? You said the 5700 limit would drive you nuts, what kind of rpm would you rev this engine to? Is there a particular brand of rod bolts that should be considered?

    Can I have these heads milled and just recut the oring grooves? One of my best friends owns and operates a machine here and allows me to kind of come and go as I need, and do whatever I need done that I can't do myself.

    I am a premix believer so that is one worry out of the mix.

  9. #9
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    Oh, and thank you all for responding. I love outboards and boat better than any 1/4 mile drag car or open wheel/late model dirt car I have ever driven and could talk and research them for hours....so keep talking and I will happily keep taking notes!

    Thanks again

    Slimm

  10. #10
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    You will have torque to yield bolts on the rods that came in your motor. They are one use bolts. You will need to replace them with either the older style reusable bolts or new torque to yield style. Good bolts, some 40:1 premix and metal caged rod bolts and you can twist it up to 7000 RPM without a problem.

    There are shops that specialize in doing O ring heads. Jay Smith will do them. Maybe Carson or Rucks. Its not something you'd do on your own without a CNC program set up for it. Its a pretty complicated gasket set and not just the cylinders. Its cheaper and easier to have your block machined to fit old heads and buy some old style heads than it is to machine your heads and recut them for the O rings cylinder and water gaskets.

  11. #11
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    You won't have ta worry 'bout turnin' it up. Its an 'lectronic motor and will be what ever it will be. Probably 6 grand or less. Without being able ta turn tha wick up it really won't do much if ya change anything.......

  12. #12
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    Thanks tlw, and everyone who has responded. I know I am grabbing at a lot but I love learning as much as I can and once I get started I can't stop. I am now on a mission to find out what heads will swap onto my block. Does anyone have any experience with the tuners I have seen like the mad efi one? Is this just a type of exhaust tip that empties out into the mid section and replace the entire liner or does it coincide with the factory liner? What are the performance benefits, mid and upper rpm improvements or bottom end?

  13. #13
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    The stock tuner is probably a 7"/8" inch tuner. Putting a shorter one on there won't do you any good and make it a dog down low if it does anything. With the factory electronics you will be RPM limited. If you "retrograde" to the old style electrics you can get around that. Just takes a little shopping in the classifieds and ebay.

  14. #14
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    Solid mounts
    Nose cone, tab the skeg
    TDR or Carson reeds

    Leave the rest alone and enjoy it, spend some money on a good prop.

  15. #15
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    Quote Originally Posted by Capt.Insane-o View Post
    Solid mounts
    Nose cone, tab the skeg
    TDR or Carson reeds

    Leave the rest alone and enjoy it, spend some money on a good prop.
    "tab the skeg" I do not know what that means...can ya gimme a clue?

    Thanks
    Slimm

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