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1977 Johnson 55hp stalls at idle and won't rev over 1200rpm

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  • 1977 Johnson 55hp stalls at idle and won't rev over 1200rpm

    Hello everyone, I'm new to boating this year. I purchased an old trihull and an unknown condition Johnson 55hp 2 cylinder. So far I've replaced the coils, stator, plugs (ngk 2129), fuel pump, rebuilt carbs and changed jets to the size listed in the parts manual. I tried to take this boat out last week and couldn't get it to idle without misfiring and stalling. Also top speed was around 7mph at 1200rpm. The week before I had it running around 24mph. Not sure where to go from here. I have tried synching the carbs and the throttle linkage to the cam. Cylinders are at 110psi and 115psi compression. Base timing was set to 4* btdc. Not sure what full advance is as the manual says don't rev the engine with no load. Any help is appreciated.

  • #2
    Compression should be 140 + on those.-----Time to remove cylinder head in my opinion.

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    • #3
      So you think it's a head gasket failure ? Is that a common thing with these? If it is a worn out powerhead I may just junk it.

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      • #4
        I say the compression is low.------Perhaps a bad gauge ?------Up to you to do the trouble shooting and inspection as I can not see or touch your motor.

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        • #5
          Why did you re-jet the motor? 140 psi is on a brand new rebuild so yours may not be bad. Did all this happen after you worked on it?

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          • #6
            The gauge is ok I think. It doesn't get used much and is well built.

            I rejetted because when I did the carbs the Jets were no. 58 but the manual calls for 54D jets.

            Also the carbs are the adjustable idle mixture type not what originally came on the engine. I simply swapped the Jets from the original carbs that came with it but we're not installed on the engine.

            Before I did the work it didn't want to idle either but it had a lot more power. Maybe the Jets are too small. The first time I had it out I had to raise the idle speed and advance the base timing all the way to get it running strong enough to not stall when put in gear.

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            • #7
              Now, what you fail to realize is the jets go with the carb. Put the old ones back in do a link and sync and adjust the carbs.

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              • #8
                Ok I can do that no problem. However even before it wasn't idling correctly. What about the Reed valves ? Do they ever go bad ? Even with the other jets installed it wasn't running right.

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                • #9
                  Why aren't you using the original carbs?

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                  • #10
                    Originally posted by Chevyls6 View Post
                    Base timing was set to 4* btdc.
                    What are you referring to as Base Timing?

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                    • #11
                      Originally posted by flyingscott View Post
                      Why aren't you using the original carbs?
                      The originals have damaged throttle shafts. It was just easier to run the carbs that were on it.

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                      • #12
                        Originally posted by jimmbo View Post

                        What are you referring to as Base Timing?
                        The timing at idle with the throttle fully closed and timer base adjuster screw against the stop bracket.

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                        • #13
                          Misadjusted Timing and Wrong Carbs, Gee I wonder why it isn't running well.

                          Any idea what the carbs you are using are off of?
                          Does it have a Spark that can jump a 3/8" gap?
                          Are both carbs getting Fuel, floats properly adjusted?

                          Broken/bent Reeds are not a common problem. A bad reed reveals itself by spraying fuel out of the carb throat

                          Do you have the correct(factory) service manual?

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                          • #14
                            Originally posted by jimmbo View Post
                            Misadjusted Timing and Wrong Carbs, Gee I wonder why it isn't running well.

                            Any idea what the carbs you are using are off of?
                            Does it have a Spark that can jump a 3/8" gap?
                            Are both carbs getting Fuel, floats properly adjusted?

                            Broken/bent Reeds are not a common problem. A bad reed reveals itself by spraying fuel out of the carb throat

                            Do you have the correct(factory) service manual?
                            Rudeness is not appreciated. I did my best to adjust the timing with the info I had. I used the 3* +/- 1* from Mr Joe Reeves. It wouldn't idle at all with the timing any more retarded than that.

                            I don't know what the carbs are from but they have fixed main jets, adjustable idle jets, and the same bore as the originals. Spark has not been tested over a 3/8 gap but I will. Both carbs have fuel and the floats were set according to the seloc manual. I've been using a multi-year / horsepower manual I bought online not the exact factory manual.

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                            • #15
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                              Just for your info and for you to do more research.-----Timing at idle does NOT matter and looks after itself.-------Throttle opening relative to timing does matter.-----And MAXIMUM timing advance is the only timing you set.----Maximum timing is set at the factory and rarely if ever needs adjusting.

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