1977 Johnson 55

[Timguy]

Hi, this is an intermittent problem that turned permanent. Good compression and spark. Motor won't run above 2500 rpm. Even if I unplug the temp / rpm limiter. Checked wire back to controls from limiter sender and it is open.......any ideas? Stator, trigger, power pack, and coils all test good. Maybe a coil shorting out at higher rpm? But I've changed both coils 2x. Techs at Marine Engine.com think I'm a fool. I've got almost 400 posts at that site, I think I'm gonna give them up. Please help. Thanks, Timguy

 

[boobie]

Re: 1977 Johnson 55

Have you done a cylinder drop test on it to see if it's running on both cylinders ??

 

[Timguy]

Re: 1977 Johnson 55

Yes and both cylinders are pulling.

 

[Timguy]

Re: 1977 Johnson 55

The first time I had the motor, I rebuilt the carbs and replaced the fuel pump. It ran great for the customer for 2 days. The it suddenly acted up with the low power again, just like before. That led me to think that I was not on the right track as intermittent problems tend to be electrical related. I tested all spark components and all passed with flying colors. I also changed both coils as one of them had a crack. I tested the boat again with no improvement. I had a new power pack so I tried that too, no luck. Checked flywheel as I've heard that sometimes the magnets can become too weak, thus affecting the trigger pulses. Magnets seem strong. Also tried manually advancing the timing past the normal range.....that helped bring on more power but still only about 50 percent. Seems I was on to something, then the guy wanted to bring the boat to someone else. Found out later that he gave up too.
What do you think? Does this motor have the wrong ignition system? Looks like a 1979 motor with a 1977 ignition. But that wouldn't explain why it ran great for 2 days after the fuel system work. How does the high temp rpm limiter work? Thanks, Tim

 

[Timguy]

Re: 1977 Johnson 55

Hi, anybody out there? Have I got any help from you fine techs?

 

[Joe Reeves]

Re: 1977 Johnson 55

That engine DOES NOT have a high temperature rpm limiting sensor. The TAN wire that you are unplugging at the cylinder head is simply a overheat sensor that would cause the warning horn to sound steady and constantly should the engine start to overheat.

What spark plugs are you using and at what gap?

Remove the spark plugs... check the compression. What is the reading of each cylinder?

With the s/plugs still removed, the spark should jump a 7/16" gap with a strong blue lightning like flame... a real SNAP! Does it? You can approximate the gap by using a medium #2 philips screwdriver plugged into the spring connector that normally grabs the top of the s/plug, then holding the screwdriver shank 7/16" away from the powerhead.

NOTE: Checking spark with the spark plugs is a waste of time!

You say the engine ran good for two days after rebuilding the carburetors. Sounds to me like something let loose and is affecting the carburetors again.... fuel line deteriorating internally, a small bit of debris being drawn into a high speed jet, something of that nature.

 

[Timguy]

Re: 1977 Johnson 55

Thanks Joe, your the best of the best, regards, Tim