Johnson 70HP 1988 low power on first run of the day

[BarryBarrie]

I have a 1988 Johnson 70 HP (Model number CJ70TLCCA) with VRO. Symptoms are: On the first run for the day, i.e. cold start and 5 minute warm up, the engine idles perfectly. Then throttle up it will max out at some low RPM, guessing 2500 rpm (no tach.). The boat will not plane. It will hold this condition for a few minutes and then like a switch will kick into full power and away we go. It rarely repeats this condition the same day and not until the next morning will I experience this again.<br /><br />Sometimes when it is about to kick into full power, you can tell it is about to happen as there are short intermittent burst of power for a fraction of a second.<br /><br />The owner's manual explains the function of the RPM limiting safety feature to protect the engine from burning out from lack of oil or over temperature and I suspect the problem is related to this protection feature. However, I am at a loss on how to diagnose or trouble shoot to confirm this. The over temperature alarm does work (found this out when the water intake once plugged with weeds) but is not sounding when the low rpm condition exists. <br /><br />This condition was first noticed 4 or 5 years ago (very minor) and what worries me is that it is taking longer each year. The oil consumption seems normal.<br /><br />The surprise last year was that the first run after taking from storage and the (very embarrassing) smoke was still thick in the air from burning out the winterizing fogging - not a problem! Full power right away. But the next day was a different story.

 

[Blueclaw]

Re: Johnson 70HP 1988 low power on first run of the day

sounds like one of your plugs is partially fouled then clears up. when was the last time you changed the plugs or cleaned and gapped them?<br /><br />the other thing would be to take a timing light and check for a steady spark pulse on each cylinder wire when this happens.<br /><br />Once the motor goes into slow mode you have to turn the key off to bring it out of that mode so I wouldn't think that is your problem. <br />The other thing it could be is a sticky float in one of the carbs

 

[kevin88]

Re: Johnson 70HP 1988 low power on first run of the day

Is it possible that your triggers are out of adjustment. I have experienced this same exact problem a few times and wondered if water condensation under the flywheel could be enough to throw the triggers off... and it seems as if after time when the water evaporates the motor kicks in as normal..

 

[BarryBarrie]

Re: Johnson 70HP 1988 low power on first run of the day

Kevin, Thanks for the suggestion. But please clarify - are the triggers you are referring for the ignition? i.e. the solid state points? I guess a test for this theory is to open the cover in the morning and let the sun warm/dry things out. Other than the potential electrical shock, a hair dryer should speed up the test! Did your problem go away on its own?

 

[BarryBarrie]

Re: Johnson 70HP 1988 low power on first run of the day

Responding to Blueclaw...<br />Thanks for the hint regarding the slow mode can only be cleared by turning the key off. This makes good design sence and I missed this detail in the manual.<br /><br />Re: plugs - I'm sure I've had them out and don't remember them looking odd. But they are relatively cheap to replace so I'll do it regardless.<br /><br />Re: Timing light - I haven't got one but will check into purchasing one. The problem might be that by the time I get through the 3 cyclinders, the problem may clear up. Should the missing pulse be observable during idle? What about pulling a spark plug wire one at a time? I've read on other postings warnings about this damaging the spark unit (power pack?) - is this true?<br /><br />Re: carb floats - I'll have a look but the boat is still in storage and 2 hours away. I'll have it out for the first run this Sunday.

 

[kevin88]

Re: Johnson 70HP 1988 low power on first run of the day

Barry. Yeah, I have a 1975 Evinrude with magneto style timing triggers under the flywheel. This is what "triggers" the power pack to fire at the correct time. My problem would go away on it's own just like yours and at first I thought it was a carb issue but now I'm beginning to seriously doubt that.<br />Also check the spark plug boot/cover connection for rust on the connection inside. Mine had a considerable amount of rust on #1 and #2 cylinders which I think has damaged my power pack.

 

[kevin88]

Re: Johnson 70HP 1988 low power on first run of the day

Barry, I have found the reason for my motor problems that were similar to yours. It was a bad ignition coil that was still sparking (weakly). I tested the resistance of each of the 4 ignition coils and my #1 coil tested high (about 200K Ohms). I would recommend a test for you but I don't know your ignition system well enough. My motor is a good 13 years older than yours. Good luck and happy hunting.