77 15 HP Johnson Intermitment SLOW speed issue

"I have a very reliable 15 HP

"I have a very reliable 15 HP 77 Johnson that displays an intermittment (about 1 in 7 trips) slow speed issue. What happens is that the motor starts fine but seems to idle slow and then moving into forward or reverse the engine will run at 20% of full power at wide open throttle and then suddenly anywhere from 2-10 mins later it will "jump" into full speed. I can't figure out why it does this. I check the fuel, seems fine, I turn off, restart and that doesn't fix it. Just seems to randomly fix itself and literally jump back into full speed. It did this last year and even after a new carb, new plugs, new tank/line, new water pump and new prop (over the winter) it still does this once in a while. Very frustrating as I use my boat to get back and forth to an island cottage and have to cross a busy boating channel so i'm a sitting duck when going at 20%.. Anyone have any ideas on what I should check given we overhauled quite a few things over the winter? Note that motor starts perfectly on first pull and this often happens a few hours after I used the engine. Thanks in advance!"

Pull apart all connectors to t

Pull apart all connectors to the power pack and check for 'burn marks' between the connector pinns bothe in the male and female connectors. Sounds lke a cylinder is dropping out no and then.

"Hi Morten - thanks for the ti

"Hi Morten - thanks for the tip. It seems like the engine is going at 700-900 (20% or so) RPM when this happens.. If a cylinder was down, wouldn't it be revving much closer to half speed? Thanks for the tip!"

"It may not completely loose t

"It may not completely loose the cylinder, just som missing now and then. As for revs on one cyl, depends a bit of the load."

"Hi Morten - thanks for the re

"Hi Morten - thanks for the response. What would explain the engine suddenly "clicking" after a few minutes and accelerating to optimum (scary when this happens as the whole boat lurches)? I did notice that this problem only happens after a start (never happens after it is running normal). I suppose I could pull out the plug boot when it happens next time to isolate if one of the cylinders is down. Do you still suspect a faulty powerpack? I'm a novice when it comes to this stuff Thanks!"

"A powerpack is much like a li

"A powerpack is much like a light bulb, works or not. I suspect You may have a bad/corroded conection somewhere, in the plugs, power pack ground wire, stop circuit... Take apart and clean all connections."