1985 Johnson 150 problems....

Hello everyone! I just discovered this forum and WOW!! What a great wealth of information. After reading through a bunch of threads that were similar to my problem, I figured I would register and post as many details about my problem as possible.

Motor is a 1985 Johnson 150 VRO disconnected running on 50-1 ratio. Compression is 105-115 in all 6 cylinders. Carbs were rebuilt 20 hrs ago, new water pump kit and gear oil, new NGK plugs. Boat is an 18' Hydra sport CC.

My problem comes and goes, it is a surging and erratic running at any throttle range. I will be running fine and then the motor will drop rpm and run barely on plane then it will surge into more rpm where it should be. Then it goes right back to lower rpm. Doesn't sound like its running smooth either. Even at idle(in gear) it is rough and jolty. I replaced the water seperator with a new one(whole thing, not just filter) and it ran without issue for a few outings. Now it is back to the same problem as before?? I have tried pumping the primer ball while having the problem with no change. Primer bulb never really gets that firm though and I have tried 3 different brand new bulbs of 3 different brands so I think the bulb is ruled out I did notice a spark arcing from the top left cylinder coil. It was arcing from the orange wire lead to the boot that connects to the coil and leads to the spark plug boot. I have since remedied the problem with a new rubber boot around the orange wire end.

Any help is MUCH appreciated. And of course I'm sure I missed something so ask away.....

Re: 1985 Johnson 150 problems....

I think those are the wrong sparkplugs.

I would draw some fuel and let it settle in a glass, check for water.

Given the ignition leak you witnessed I'd start by getting a spark tester from the auto part store , set the gap to 7/16th inch and test each coil.
I suspect you'll find weak spark.

Check the coils for cracks, this usually requires removing them and looking very closely, check the mounting is clean (ground).

A timing light can show a weak ignition whilst running but I like the gap tester.

Re: 1985 Johnson 150 problems....

The fact that the seperator helped, but not permanently, suggests fule problems: 1. old fuel (more than 2 months?) 2. water accumulating in tank or 3. (if tank dried out) water getting in tank.
Run some fuel from the tank into a clear bottle and let it settle (sometimes the funky stuff is below the pick-up and only gets inthe system when you are bouncing around, getting on a plane, etc.)
So get rid of the fuel, dry out and clean the tank (carb cleaner and a rag on a stick) and refill; switch filter and go. Watch for points of entry for water: suspect the fuel cap and vent. If you have a vent on the side of the hull, deal with that first.

Re: 1985 Johnson 150 problems....

My 81 model 175hp had the same issues with the coils arcing.
They looked fine and even tested ok with a spark tester.
I found the problem by running the motor in the dark and could see sparks jumping to the cylinder head from the sides of the coils..

I think you may have fuel and ignition problems going on at the same time.
Just a thought...

Welcome to Iboats!!

Re: 1985 Johnson 150 problems....

How was it before the carb rebuild ???

Welcome to iboats.

Re: 1985 Johnson 150 problems....

Thanks everyone. I will get a spark tester on the way home from work today and report back. Fuel is fresh, I boat at least once a week. I also add startron treatment each fill up(not perfect, but I'm sure it helps a little). It ran well before the carb rebuild, but it also ran real well after the carb rebuild up until the last few trips.

Thanks,
Aaron

Re: 1985 Johnson 150 problems....

Spark is great! I put a new water separator on it just to be sure. I will be testing it after work tomorrow. It runs fine on the muffs(as always

Aaron

Re: 1985 Johnson 150 problems....

Ignition problems tend to show up when the engine heats up (reaches normal operating temps.) These type problems can be intermittent till the bad component fails. As Jones mentioned, a spark checker is a good test tool, and the timing light will show spark on each plugwire when running. An arcing coil is a candidate for replacement and calls for checking the others in darkly lit conditions.