• If this is your first visit to the iboats.com Boating Forums, be sure to check out the FAQ. To post a question or comment, begin by signing up. To start viewing messages, select the forum that you want to visit from the selection below.


Announcement

Announcement Module
Collapse

Help Tip: If you have a question that has not been answered to your satisfaction in the archives, it is always best to start a new thread of your own. By starting your own thread, you will receive the maximum number of views by forum members.

Below are some additional forum policies in hopes of all iboats members will follow, Thank you.

1. Please do not reply to old topics or hijack existing topics. Old topics of a technical nature are like a library book, Please do not write in them.

2. Old topics should be considered archives and used for reference only. Please do not reply to them.

3. Do not take over someone elseís topic (aka hijack) with your own question, even if it is similar. If you have a question that has not been covered to your satisfaction in the archives, it is always best to start a new topic of your own.

4. If you have a question for the original poster (OP) and the topic is over 30 days old, send the OP a PM, he may not even visit the forums any longer, or may not notice your question in the old topic.

5. By starting your own topic, you will receive the maximum number of views by forum helpers that may not even notice your question when itís posted at the end of someone elseís topic. And those answers will be specific to your particular issue.

6. Please do not post to topics that have been inactive for more than 3 months unless you are the original poster. We have very active forums and any topic that remains inactive for that long should be considered "dead". It is especially confusing when there is an entirely new question posted to an old topic.

7. Posting at the end of any topic is considered to be hijacking the original posters topic which in turn subjects the topic to be closed if it continues to happen thus not making it fair to the original poster in the future had for some reason he/she needed to return for additional information or provide an update of the problem solved which is always welcomed within a reasonable amount of time frame.

8. Please note that you should see a red banner pop up near the bottom of each inactive topic asking you not to reply to old topics. The Red banner will read: Please note this topic has been inactive for 90 days. For the best results, please start a new topic.

Thank you all in advance for doing your part in helping iboats run a smooth ship.

Additional forum rules linked below.
http://forums.iboats.com/forum-rules-guidelines-405/
See more
See less

GT johnson 150 losing power

Page Title Module
Move Remove Collapse
X
Conversation Detail Module
Collapse
  • Filter
  • Time
  • Show
Clear All
new posts


  • GT johnson 150 losing power

    i have a procraft bass boat with a Johnson GT 150. it runs good for a couple of minutes at plane then power drops to idle. i can play with the throttle and it sometimes acts like it wants to have the power. a couple of times it would clear out doing that. it would act up for about a minute or two then power back to wot. i have no idea what it is but i believe it is a fuel problem. the guy i bought it from rebuilt the carbs, but don't know if they were synchronized. please help its my first boat.


  • #2
    Re: GT johnson 150 losing power

    how about the yr and model number,

    its strongly suggested to get the johnson factory manual so you know whats what under the hood.
    www.outboardbooks.com

    Don't use it until its fixed, you can melt a piston very quickly like this.
    New to you, I would go through it.

    get some simple tools,
    a timing light,
    spark GAP checker from an auto parts store,
    compression guage.

    Take compression readings, all plugs out.
    Set spark gap checker to 7/16th inch gap and test each hole, plugs out.
    Change water pump.
    Re-test the engine, monitor very closely for overheating with an infrared termometer.

    Depending on the yr, it sounds like its overheating and going into SLOW mode. Need to know yr of motor to comment further.


    Also ,change the gear oil using new seals on the drain screws.
    Examine gear lube for milky appearance, report back.
    Remove prop, check shaft for fishing line, lube and reinstall prop.
    sigpic
    See FAQ Files.
    http://forums.iboats.com/showthread.php?t=299680

    Get the genuine factory service manual.
    www.outboardbooks.com
    www.*****************

    Comment



    • #3
      Re: GT johnson 150 losing power

      the boat is a 1987 and its the original motor. i pulled the drain screws out the carbs and the fuel had water in it. could this be the problem? i dont think its running hot cause it will do it when i first fire it up.

      Comment



      • #4
        Re: GT johnson 150 losing power

        Water in the fuel system can cause problems. You should flush the entire system and see if it helps.

        Comment



        • #5
          Re: GT johnson 150 losing power

          An engine will typically run/idle with a little water in the fuel, but it will have no power when under load. Pull the fuel hose off the side of the pump and fill a clear glass with a fuel sample-about 4" tall. Let is settle for a few minutes. If there is any water in the fuel, purge the tank, fuel lines and drain the carbs. Fill with new fuel.

          Comment



          • #6
            Re: GT johnson 150 losing power

            wow yeh thats the problem, get a water seperator, its today's fuel causing that unless you have a leaky fill hose fitting.
            sigpic
            See FAQ Files.
            http://forums.iboats.com/showthread.php?t=299680

            Get the genuine factory service manual.
            www.outboardbooks.com
            www.*****************

            Comment



            • #7
              Re: GT johnson 150 losing power

              what is the best way to drain the fuel tank? will seafoam work and help after i drain it? my tank vent has a screen at 3 o clock and at six. can the water be sipping throuh this while in water?

              Comment



              • #8
                Re: GT johnson 150 losing power

                Pull the incoming fuel line off the side of the pump and let it dangle over the side of the boat into a 5 gal can. Make sure the top of the can is below the bottom of the tank in the boat. Prime the hose bulb and let it go. It will self-drain the whole tank.

                Comment



                • #9
                  Re: GT johnson 150 losing power

                  it stills does it! please help!!!!!!!!!

                  Comment



                  • #10
                    Re: GT johnson 150 losing power

                    When the engine starts to act up, do you have spark to each plug? Check each plugwire with a timing light. You can see misfires or no fires in the flashes.

                    Comment



                    • #11
                      Re: GT johnson 150 losing power

                      i think it is going into s.l.o.w mode. does this 1987 gt 150 have it? how could i bypass it? its not running hot.

                      Comment



                      • #12
                        Re: GT johnson 150 losing power

                        The later model XP/GT models with the 35 amp alternator had SLOW. Not sure if it was only on the models with single power pack or not. Your 87 has two packs. Anyway-on the models that have SLOW, both brown wires from the cylinder head temp switches signal the system of an overheat at 203 degrees and then the power pack limits rpm to 2500. You could disconnect both switches at the knife connector back by the switches to test run the engine.

                        Comment



                        • #13
                          Re: GT johnson 150 losing power

                          my motor has only one power pack one the right side from the rear.

                          Comment



                          • #14
                            Re: GT johnson 150 losing power

                            If your engine has only one pack, it is at least an 1989 model. It is likley that your engine does have the SLOW system.

                            Comment



                            • #15
                              Re: GT johnson 150 losing power

                              if it helps the motor is a white gt 150v6

                              Comment

                              Working...
                              X