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  1. #1
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    Lync on merc xr4

    I have been reading my manual on my 1989 merc 150xr4 wanting to attempt the lync and sync but first off I'm not to mechanically inclined but wanting to attempt it. The manual says tools needed are spark tester and dial indicator but my question is my buddy is telling me we can check tdc with a Dowel but I don't want to mess my engine up. I have done compression test 132 to 140 across all 6 new feul pump water pump feul lines and carbs cleaned out but still spits and sputters and won't go over 4000 rpm so I'm thinking it's the lync is out of sync also has a 3 blade 24 pitch prop on a 18 ft bass cat

  2. #2
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    Quote Originally Posted by Waylen View Post
    I have been reading my manual on my 1989 merc 150xr4 wanting to attempt the lync and sync but first off I'm not to mechanically inclined but wanting to attempt it. The manual says tools needed are spark tester and dial indicator but my question is my buddy is telling me we can check tdc with a Dowel but I don't want to mess my engine up. I have done compression test 132 to 140 across all 6 new feul pump water pump feul lines and carbs cleaned out but still spits and sputters and won't go over 4000 rpm so I'm thinking it's the lync is out of sync also has a 3 blade 24 pitch prop on a 18 ft bass cat

    Checking TDC with a dowel isn't as accurate as testing with a dial indicator because the piston comes to the top of the cylinder and will dwell there for a short time while the crankshaft continues to rotate, I cannot tell you a specific number of crankshaft degrees of rotation but it could be from 1 or 2 degrees to 5 or 6 degrees or more. With the dowel all you are doing is finding the highest point of travel, NOT the center of the time in crankshaft degrees the piston stays there while the crank continues to turn.

    With the dial indicator you can see when the piston reaches the highest point and use that information to reverse the crank rotation in order to bring the piston back down the bore to a specific distance away from it's highest point. Once you have made sure you are at that distance, you can check the flywheel and timing pointer to make sure the timing pointer is aligned with the mark on the flywheel that correlates to the location of the piston in relationship to it's highest point of travel in the bore.

    I hope you understand that, I am lacking sleep and typing one eyed.

    Slimm
    Hire the handicapped, we're fun to watch

  3. #3
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    Thanks slimm perfect explanation I see now that a dowel using the best idea guess I'll have to break down and invest in some tools thanks again

  4. #4
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    Quote Originally Posted by Waylen View Post
    Thanks slimm perfect explanation I see now that a dowel using the best idea guess I'll have to break down and invest in some tools thanks again
    You are welcome Waylon, glad I could offer some insight.

    Slimm
    Hire the handicapped, we're fun to watch

  5. #5
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    And most people say take the idle stabilizer module off because it make the process more complicated and they can hurt the engine if they go bad.

  6. #6
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    I made an indicator using an old spark plug, breaking out the porcelain and welding a tab to it. I zip-tie a dial indicator to it as a depth gauge. There's a thread about it on here somewhere.

    I have an XR4 with a little less compression turning a 26" high five at over 6000 rpm on a Tracker FS1800. Not exactly a light boat.

    It's pretty easy to get 170 hp or so with good tune, but I think you may have actual faults in your ignition or fuel system.
    To fish or not to fish? What a STUPID question.

  7. #7
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    I had a feul issue the fuel line had collapsed on the inside and was restricting fuel so I changed that but haven't tried it out yet because buddy is telling me I could burn it up if it's not running right but timing is set at 23 with advanced module removed and all new plugs and so on with y'all's experiNce should I break down and bring it to someone or can I at least try it out before making that decision I'm on a fixed income so every Doller saved goes into new restoration parts for boat thanks in advance

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