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  1. #1
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    1990 GT150 RPM Increases With Trim Up

    1990 Johnson GT150 on a 1984 Ranger 350V
    Model: J150STLESB Serial: 08594609

    This has I believe been an issue since I purchased this boat 2 years ago and have been trying to figure it out. I will do my best to explain it but if you have any questions I'll do my best to answer and I can perform any inspections or operations with some guidance. Anyway the engine since I purchased it has ran fine on muffs out of the water but when I put it in the water it will die almost immediately off the trailer (I've now decided I believe that is because I trim it down) but then I could get it to restart and run around the lake for as long as I would like but once I put it into neutral and let it get back down to idle it dies and will not restart. I recently got the tach functioning again (the regulator was faulty) and the idle with the engine trimmed all the way down on muffs was maybe 500 RPM and from what I've read they will lose ~150 RPM in the water because of the back-pressure so I can see why that would stall it out. I have now raised the idle to ~1000 with the motor trimmed all the way down, but then I noticed that as I trim the motor up it will pick up RPM, roughly 2000-2200 right around when it gets out of the fine trim adjustment area, then it got all the way up to 3500 RPM when I had it trimmed nearly all the way up before I trimmed it back down to control the RPM increase.

    Work I have performed includes new fuel and oil lines (and bulbs), spark plugs, carb rebuild on all three, and the most recently replaced voltage regulator. The engine is still using a VRO system, I can't think of anything else relevant but I'm happy to answer any questions. This may be normal but it just seems odd, this is my first outboard.

  2. Ohio Fishing Reports Moderator omcforever's Avatar
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    Nov 2007
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    Miamisburg Ohio/Formerly Aiken SC
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    #2
    Quote Originally Posted by Commando Solo View Post
    1990 Johnson GT150 on a 1984 Ranger 350V
    Model: J150STLESB Serial: 08594609

    This has I believe been an issue since I purchased this boat 2 years ago and have been trying to figure it out. I will do my best to explain it but if you have any questions I'll do my best to answer and I can perform any inspections or operations with some guidance. Anyway the engine since I purchased it has ran fine on muffs out of the water but when I put it in the water it will die almost immediately off the trailer (I've now decided I believe that is because I trim it down) but then I could get it to restart and run around the lake for as long as I would like but once I put it into neutral and let it get back down to idle it dies and will not restart. I recently got the tach functioning again (the regulator was faulty) and the idle with the engine trimmed all the way down on muffs was maybe 500 RPM and from what I've read they will lose ~150 RPM in the water because of the back-pressure so I can see why that would stall it out. I have now raised the idle to ~1000 with the motor trimmed all the way down, but then I noticed that as I trim the motor up it will pick up RPM, roughly 2000-2200 right around when it gets out of the fine trim adjustment area, then it got all the way up to 3500 RPM when I had it trimmed nearly all the way up before I trimmed it back down to control the RPM increase.

    Work I have performed includes new fuel and oil lines (and bulbs), spark plugs, carb rebuild on all three, and the most recently replaced voltage regulator. The engine is still using a VRO system, I can't think of anything else relevant but I'm happy to answer any questions. This may be normal but it just seems odd, this is my first outboard.
    Did you set float drop and height per your OMC repair and service manual? Did you clean all orifices(idle-mids-mains) and their passages)? Did you use real OMC rebuild kits(new gaskets-needles and seats-ect)? Was link and sync verified? Was carb sync verified per your OMC manual? I would check and service the 6 fuel re-circulation valves on the front of the intake per your OMC manual as well. Did you install Champion QL77JC4 plugs gapped at .030? And oh yeah,,, has a compression test been done on it? Since it has been like this since you got it,,, I would verify all the above.

    Age and treachery will always overcome youth and skill !!

  3. Member
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    #3
    I believe I did set the float drop correctly, when I installed the new floats I made sure the floats were flat/parallel with the bottom of the carb when the carbs were upside down, and yes it was OMC kits. I did clean all orifices and passages with air. I don’t remember the specific Champion plug but that sounds correct and I know they were gapped to .030. I have not done a link and sync given how well it runs out of the water all of that seems to be in order. I have not heard of the recirculation valves until right now and after some searching the very small brass reed valves on each cylinder is what you’re referring to? I’ll look into those, and no I have not performed a compression or leak down test. While I have owned it for two years due to other projects on it and floods last year I have only actually had the boat on the lake a few times.

  4. SC Club Moderator ChampioNman's Avatar
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    May 2004
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    Crawfordville, FL/Lake Hartwell, SC
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    #4
    I would test the recirc valves.

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