1987 Johnson 200 runs rough

[briantedder]

I have a 1987 Johnson (I mix 50:1) The boat runs good at idle. The problem starts about 3-5 minutes after I am running at almost full throttle. The motor starts shaking really bad and slows down. It will run fine just above wake speeds but you cannot go any faster it just shakes and won't let you go any faster. I will then cut the motor off for about 3 minutes, then crank the motor back up and then begin to go full speed, and it does fine. <br />Last summer when I first bought the boat, It did the same thing the first time I tried the boat out, after that happen I replaced the spark plugs and it was fine until now, but I was thinking it is just a coinscience, and not the spark plugs at all?

 

[16Pilot]

Re: 1987 Johnson 200 runs rough

is it fouling the plugs and how is the fuel pump,line etc...? Im not a pro but my neighbor ran into a similar problem and it was his primber bulb as silly as that sounds.

 

[angus63]

Re: 1987 Johnson 200 runs rough

Around 1987 is when S.L.O.W. was introduced. If you are limited to 2000-2500 rpm when this happens, check your manual to see if this motor has slow. Slow is reset when you turn off the motor so it matches your symptoms. Do a search at the top of the page for "slow" and you'll get plenty of info.Does your alrm sound? Have you verified your overheat and vro alarm is working?

 

[BrianTindall]

Re: 1987 Johnson 200 runs rough

Look for the power pack(s). The S.L.O.W. system uses one power pack between the cylinders right behind the flywheel. If you have two power packs (midway down the block on the outsides) you don't have the slow system. Do you have a temp gauge or warning horn? Is the horn going off? Try and borrow a temp gun a check BOTH cylinder heads. A faulty S.L.O.W. temp sensor can cause this problem.

 

[briantedder]

Re: 1987 Johnson 200 runs rough

Thanks for the help!!!

 

[Dhadley]

Re: 1987 Johnson 200 runs rough

1987's did not have SLOW.<br /><br />Post the model number. Perhaps you have a newer motor than you think (lets hope so!).<br /><br />What spark plugs are you using?