1990 Johnson 60 - rebuild?

very limited knowledge when it comes to engines so I need your help.

My 1990 Johnson 60 has some trouble starting and smokes considerably until warmed up. I am not the original owner so do not know the history or past care or repairs. Typically I run this at low speeds (it is on a 20' pontoon boat).

Mechanic says the compression on cylinders 1 & 3 are over 100 and cylinder 2 is at 85. Should I care?? He mentions the VRO as the culprit but from what I have seen on this site I am inclined to disagree. He has recommended replacing the VRO as a minimum and suggests rebuilding the engine is in order (something about scoring in cylinder 2). Any suggestions will be much appreciated.

Thanks

Re: 1990 Johnson 60 - rebuild?

First off, fire the mechanic. He's clueless. Think about it, the oil injection injects oil before it hits the carburetors. Ask yourself, how can that effect one cylinder???

The OMC "triple" is very sensative to overpropping. That engine needs to be able to rev, even if you do not run it fast. The first clue is that it is on a pontoon. I'll bet it is overpropped. You need to prop it so that it can turn at least 5500 RPM at wide open throttle. 5800 would be better. As a rule, one inch of prop pitch equals 200 RPM up/down.

With that, before you tear into that engine-decarb it. See the instructional link below.

http://forums.iboats.com/showthread.php?t=158076

Re: 1990 Johnson 60 - rebuild?

what oil are you using, the synthetics smoke less. smoke is normal on start up. i agree with the decarb, especially if it's run slow for extended periods. also prop it correctly.

Re: 1990 Johnson 60 - rebuild?

I agree, you need a new "mechanic".

The 56 cid motors tend to have higher combustion temps in the middle cylinder especially when running 1/2 or 3/4 throttle. What we've done in the past to help the situation is richen up the mid range a couple numbers.

There were several bulletins on that motor. I'm really not surprised your "mechanic" didn't mention them. He probably doesn't know about them.

The guys are also right on about rpm. I'd suggest 5800 as a minimum target. Again it has to do with combustion temps, regardless of what rpm you're cruising at. They're also correct about the decarb.

On that motor using the correct spark plugs is critical. With everthing else he has, and hasn't, told you I'd sure check to make sure he has Champions in it. In this case I'd opt for the slightly cooler QL77JC4's.

I bet you're wondering why the combustion temps would be higher at cruise than wide open. About the mid 3000 range you'll reach full advance timing. But you're running on a relative small amount of fuel. At full throttle you're dumping more fuel and that helps cool the combustion temps down. Remember we're looking at combustion temps as well as cooling water temps. Two different things.

If you even speak to the "mechanic" again ask him how the oil injection picks on one cylinder on an OMC. I'd really like to hear that explanation.

Re: 1990 Johnson 60 - rebuild?

You folks are fantastic and your help has been invaluable to a guy who has been at the mercy of the "mechanic"

I don't consider myself mean spirited, but I had a good chuckle over the 'hand caught in the cookie jar' reaction when I told him why I disagreed with his theory on the VRO. Bonus chuckle when his son came out from the shop area to help me out and he commented on the nice motor I had.

Anyway, the prop store agreed they had sold me the wrong prop for a pontoon boat and are working with me on a swap.

I picked up some XD30 (wasn't sure of the difference with XD50) and will get rid of the old oil in the tank. Next step is the decarb and change out the plugs to the ones you recommended.

I can't thank you guys enough !

Re: 1990 Johnson 60 - rebuild?

We'll be here. Don't be a stranger, keep us posted on your progress.

Re: 1990 Johnson 60 - rebuild?

MVM said:

the 'hand caught in the cookie jar' reaction

Click to expand...

Too funny!

Re: 1990 Johnson 60 - rebuild?

Looks like they got gaught in the act. Get all you can from themand never go back.