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Thread: OMC Tech - Help

  1. #31
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    Could be the ign module/power pak had the same thing going on with a 150 fastrike ?
    I may be slow but im ahead of you. *hit's only ankle deep but you went in head first.

  2. #32
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    Quote Originally Posted by racervboat View Post
    Could be the ign module/power pak had the same thing going on with a 150 fastrike ?
    that was my original hunch. If the entire fuel system has been gone through, the only logical thing left would be ignition. i've noticed these motors like to mimic a fuel issue when it's often ignition which is why i like to rule ignition out first since it's the easiest to test...

  3. #33
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    Just another thought: you say it's bogging around 1,200rpm to 2,500rpm. that could be the shift interrupter switch shorting out, or the quickstart malfunctioning somehow. i'd swap a powerpack from your good motor and see what happens.

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  5. #34
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    Was thinking quick start issue too maybe.
    I may be slow but im ahead of you. *hit's only ankle deep but you went in head first.

  6. #35
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    Interrupter is a good point.. I have seen one with the cable adjusted too tight engage the switch when the motor pulled back in the mounts as you accelerated. will definitely fall on its face when you drop 3 cyls..

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  8. #36
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    Does omc mess with different jets port and starboard? I can’t remember on that motor.

    checking the ignition isn’t a bad idea. But low rpm appears to work and high rpm appears to work.

    yea, fast start would cause power loss through timing, ok pull the temp wire and see if she runs. You can also disable the fs advance umm fs shouldn’t be active when warm though so it shouldn’t actually effect it. That could be the problem though.

    also never rule out cleaning the carbs again, I’ve done it 3 times before finally found rust in the fuel tank.

  9. #37
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    Quote Originally Posted by Motv18 View Post
    Does omc mess with different jets port and starboard? I can’t remember on that motor.

    checking the ignition isn’t a bad idea. But low rpm appears to work and high rpm appears to work.

    yea, fast start would cause power loss through timing, ok pull the temp wire and see if she runs. You can also disable the fs advance umm fs shouldn’t be active when warm though so it shouldn’t actually effect it. That could be the problem though.

    also never rule out cleaning the carbs again, I’ve done it 3 times before finally found rust in the fuel tank.
    There is a temp wire you can pull that disables the fast start? I know the shift interrupter works because I tested it by pushing in the pin. Seems to drop 3 cylinders. I guess I can disconnect the switch and see if that works. Thanks again. Got a bunch of stuff to test. Will bring it down to the water and try some of these. Wont be until Tuesday though. Travelling this weekend. Really appreciate the help. Some really great ideas. Paul

  10. #38
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    Quote Originally Posted by PaulO View Post
    There is a temp wire you can pull that disables the fast start? I know the shift interrupter works because I tested it by pushing in the pin. Seems to drop 3 cylinders. I guess I can disconnect the switch and see if that works. Thanks again. Got a bunch of stuff to test. Will bring it down to the water and try some of these. Wont be until Tuesday though. Travelling this weekend. Really appreciate the help. Some really great ideas. Paul
    Yes. Port side temp sender wire black/white. then ground it to the block with a jumper wire. i think that did the trick for me. easy to tell if it worked... timing won't digitally advance when its idling

  11. #39
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    Only accurate test for interior or is to unplug one wire.

    Switch may be fine but cables out of adjustment may not activate it properly.

    It kills entire starboard bank.

    Jetting is same on both sides.
    I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.


    I refuse to allow common sense to interfere w/my boat buying decisions.


    Checkmate 16' 140 Johnson
    Hydrostream 17' Vector FrankenRude I
    Laser 480 (?) 21' w/GT 200
    Glastron Carlson Conquest w/XP 2.6
    Glastron Carlson CVX 20 w/XP 2.6
    24' Sonic w/twin 250 Johnsons
    24' Sonic w/twin 250 HO Johnsons
    19' STV River Rocket w/FrankenRude II
    Allison XR 2002 w/Frankenrude II
    Hydrostream 18' V-King w/Frankenrude II

  12. #40
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    Okay update time. This motor is one of a pair on my boat. The port motor has always run flawlessly. This motor has always been trouble for as long as I have had it and although I have had it for a long time, it doesnt correspond to more than 20 or so runs since it sat for a long time while the boat was gone through. Anyway, being as I have another great running motor, I have the ability to swap parts in my troubleshooting and although I was hesitant to screw with a great running motor, I started swapping parts. Did a compression test on both motors. Starboard (bad) motor was all in the 90 to 92 range with one cylinder at 105. Port motor was all in the 100 range with one cylinder about 92. From all my research, the these are low compression motors and the compression is okay even on the starboard one. I verified that lower ratios were the same and that flywheels or magnets showed no damage. I concluded that I could break down the problem into the categories of either fuel delivery or spark. Since I have been through the carbs at least 4 times now, I decided to go the spark route. Swapped everything from the good motor to the bad including: spark plugs, spark plug wires, rectifier, ecu, timer base, coils, stator and flywheel. Problem remains. Bad flat spot on acceleration. Has to be "goosed" to get past it and keep it from dying. Don't think motor develops as much power as its twin even if I get it past the bog. Next step is swap carbs and throttle bodies. Almost forgot, I did a link and synch and a timing check under load. Not much confidence in the upcoming carb swap but, I have to be sure. Thinking maybe something powerhead/mechanical but don't know what. No good way to test the reeds but they look fine and there is no backfiring out the carbs ever. Temptation to fill this motor full of ak47 lead is disconcerting!

  13. #41
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    Quote Originally Posted by PaulO View Post
    Okay update time. This motor is one of a pair on my boat. The port motor has always run flawlessly. This motor has always been trouble for as long as I have had it and although I have had it for a long time, it doesnt correspond to more than 20 or so runs since it sat for a long time while the boat was gone through. Anyway, being as I have another great running motor, I have the ability to swap parts in my troubleshooting and although I was hesitant to screw with a great running motor, I started swapping parts. Did a compression test on both motors. Starboard (bad) motor was all in the 90 to 92 range with one cylinder at 105. Port motor was all in the 100 range with one cylinder about 92. From all my research, the these are low compression motors and the compression is okay even on the starboard one. I verified that lower ratios were the same and that flywheels or magnets showed no damage. I concluded that I could break down the problem into the categories of either fuel delivery or spark. Since I have been through the carbs at least 4 times now, I decided to go the spark route. Swapped everything from the good motor to the bad including: spark plugs, spark plug wires, rectifier, ecu, timer base, coils, stator and flywheel. Problem remains. Bad flat spot on acceleration. Has to be "goosed" to get past it and keep it from dying. Don't think motor develops as much power as its twin even if I get it past the bog. Next step is swap carbs and throttle bodies. Almost forgot, I did a link and synch and a timing check under load. Not much confidence in the upcoming carb swap but, I have to be sure. Thinking maybe something powerhead/mechanical but don't know what. No good way to test the reeds but they look fine and there is no backfiring out the carbs ever. Temptation to fill this motor full of ak47 lead is disconcerting!
    Last summer I took my entire blocked - off OMS pump assembly and installed mastertech's duel fuel pump setup for piece of mind. Really a strange issue you've got that's for sure. Well we know it must now be in the fuel system. i'd say if the swapped throttle body and carbs (i'd do the throttle body first, give it a whirl, then swap carbs) don't do it, i'd be out of options. anyone else? maybe a leakdown test but a high leakdown wouldn't make it stumble like that...

  14. #42
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    Damn I hate these kinda motors , seems like once in a blue moon these come along and once its figured out it's never good. but that's just in my case and my luck , but sum times it's stupid simple , anywho. Go ahead whit ur swapping, be 1 or2 more things to process elimination. good luck hope for best fer ya

  15. #43
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    Since you say you’ve been through the carbs multiple times, check the small metal plates on the sides of the carbs.
    They have a rubber gasket that seals vacuum ports.

    Yrs ago, after rebuilding a powerhead, breaking it in, tuning it (hot rod motor), Put probably a 100 miles on it in the IC and it started doing similar.
    Was single engine boat so didn’t have #2 to nurse it.

    I dropped off plane after a 30+ mile, hard run, and soon as I went to idle it died.
    Started, idled fine but wouldn’t run under load.

    Did same as you and started swapping parts after failed trouble shooting w/no luck.
    Had a good, 2nd generation, local OMC shop who I was friends with and called him for help.
    Told him I’d pay him his $90 hr rate for him to trouble shoot it.
    He asked what I did so far. He said that’s same as he would do and didn’t want to work on it.

    So a while later, at wits end, quadruple ckg everything AGAIN, I started checking those screws in those plates and damned if one of them didn’t turn a quarter turn!
    A light bulb went off in my head!
    Right then, I hooked it to the truck and towed it to the ramp.

    That was it!
    Damn thing ran perfect after that.

    What I hate about trouble shooting is, my brain says it can’t be carbs because I rebuilt them.
    Cant be powerpack, it’s new.
    What if it’s new defective??

    And yes, your compression is OK.
    I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.


    I refuse to allow common sense to interfere w/my boat buying decisions.


    Checkmate 16' 140 Johnson
    Hydrostream 17' Vector FrankenRude I
    Laser 480 (?) 21' w/GT 200
    Glastron Carlson Conquest w/XP 2.6
    Glastron Carlson CVX 20 w/XP 2.6
    24' Sonic w/twin 250 Johnsons
    24' Sonic w/twin 250 HO Johnsons
    19' STV River Rocket w/FrankenRude II
    Allison XR 2002 w/Frankenrude II
    Hydrostream 18' V-King w/Frankenrude II

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  17. #44
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    Thanks again to you guys for the suggestions and best wishes. Instigator- When I went through the carbs last time, I made certain that fuel could flow up through that little brass tube that goes from the fuel bowl to what looks to me to be the idle circuit and the intermediate circuit. Those passages go up under the plates you are talking about that are held on the sides of the carbs with (I think) five screws. There is a thick rubbery gasket under those plates. When I made sure the passages were clear, I also made sure the plates and gaskets were sealing by closing off all openings and supplying vacuum making certain they all held vacuum. Now you make me think of the similar plates that are on the sides of each throttle body that also close off the passages that allow the fuel to flow from the carbs into the idle and intermediate openings in the throttle bodies. I have checked them all for tightness and for fuel flow but not for leaks. I think when I swap the carbs from the good running motor over to the bad, I will swap the throttle bodies also to eliminate a problem with those plates/gaskets. Paul

  18. #45
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    Yep, check both.

    Ive rebuilt a pile of those carbs and only had that happen once.
    I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.


    I refuse to allow common sense to interfere w/my boat buying decisions.


    Checkmate 16' 140 Johnson
    Hydrostream 17' Vector FrankenRude I
    Laser 480 (?) 21' w/GT 200
    Glastron Carlson Conquest w/XP 2.6
    Glastron Carlson CVX 20 w/XP 2.6
    24' Sonic w/twin 250 Johnsons
    24' Sonic w/twin 250 HO Johnsons
    19' STV River Rocket w/FrankenRude II
    Allison XR 2002 w/Frankenrude II
    Hydrostream 18' V-King w/Frankenrude II

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