1987 Johnson 120hp cuts power

[Herst72]

Hi all. (I am Norwegian, so please forgive me if my spelling is bad... Here is the case: My 1987 Johnson 120hp starts fine (with some smoke), and idles at around 900 rpms. But when I put it in forward and increase throttle, the motor cuts power completely for a second, before it comes back. This may continue for 30 seconds or so, until it stops completely. The motor will restart, but with the same problem. Sometimes the problem occurs at 1000 rpms, other times it will occur at 2000 or 3000.The power is cut and comes back in very regular intervals, leading me to think that I have a problem with ignition in one or two of the cylinders. If I accelerate really slowly, the motor will run just fine, and will do so for as long as I want to run it.. But after a short or long stop, the problems will start all over again. Here is my checklist:
1) Change all plugs and cables 2) Dismantle and clean all carbs, 3) check for air leaks in fuel lines, 4) test fuel pump (how do I do that?)
Are there any other obvious things to look for? I'll be grateful for any input.
Thanks, and best wishes from Norway.

 

[petryshyn]

Re: 1987 Johnson 120hp cuts power

have you check for spark with a spark tester at each cylinder? Intermittent problems are the hardest to fix. Try simplest things first. While idling, wiggle harnesses and plugs and look for changes. Try cooling the pack down with ice and look for changes. Try heating the pack with hair dryer and look for changes.

Will it stall if you try to maintain the idle at 1000rpm?

You also may want to disconnect the kill wire to see if that circuit is playing havoc with you

 

[Herst72]

Re: 1987 Johnson 120hp cuts power

Hi, and thanks for the swift reply. I'll get started on this during this week, and keep you posted. The kill wire certainly belongs on the list over the obvious things to check..

Thanks again!

 

[tashasdaddy]

Re: 1987 Johnson 120hp cuts power

did you remove the jets when you cleaned the carbs, did you do a linc n sinc?