1987 90HP VRO Loss of Power

[swab]

I have a 1987 90HP Johnson VRO powering a 24' pontoon boat and ran into a problem over the weekend. We were out cruising on the lake and got knocked around pretty good by some cabin cruiser wakes. About 2 minutes after that, at about 3/4 throttle, the motor, all of a sudden, started running really rough and lost power. We pulled into a cove and I brought it back to neutral where is seemed to run more smoothly. We waited about an hour and started it up and it didn't seem to run as rough but once I put it under a load (going back to the marina)it ran very rough with very little power. We got back to the dock and I checked to make sure the plug wires were on and that it was circulating water and cooling. We waited about an hour and took it back out to see if it would run any better. When I did this, it seemed to run as smooth as it normally does but now with much less power. Anyone have any ideas as to what the problem may be?

 

[DJ]

Re: 1987 90HP VRO Loss of Power

First off, make sure you have spark on all four cylinders.<br /><br />If you do, remove the plugs and see if any of them appear to be washed clean.<br /><br />If any are washed clean, you either ingested some water or you have an internal cooling water leak.<br /><br />Did your fuel tank get any water in it?

 

[swab]

Re: 1987 90HP VRO Loss of Power

I don't think I have water in the gas because it seems to run fine at idle. I'll take a look at the plugs tonight and see if they looked washed out. If I did ingest water, what procedures would I take to make sure the cylinders don't corrode and no further damage is done internally? Thanks for the reply.

 

[swab]

Re: 1987 90HP VRO Loss of Power

Okay, I pulled the plugs and found something disturbing. The side electrode on one of the plugs was smashed down on the center electrode. There is a ding on the top of the side electrode and it looks like something small and hard hit it (doesn't look like the piston did it). I'm going down tonight to test the compression on all of the cylinders. So now I have a couple questions:<br /><br />1) What should my compression range be for this motor?<br /><br />2) What is the likely culprit of the damage?<br /><br />Of course everything has been fine and we use the boat every weekend and my brother and sister are arriving tomorrow from out of state so I really want to get this thing going by the end of the weekend. Any ideas?<br /><br />Thanks

 

[rickdb1boat]

Re: 1987 90HP VRO Loss of Power

The only thing that would ding the plug is the piston. Compression should be over 100 PSI. As long as they are all within 10%, you're OK...Do you have portable tanks on the back of the toon or a built-in gas tank? Motors will run fine at idle with a little water in the fuel, but will not run under a load. From personal experience a few years ago...

 

[swab]

Re: 1987 90HP VRO Loss of Power

I have a 25 gallon built in tank so draining it is going to be a bear. I can take another tank(from my jon boat) and use that for now. What would cause the piston to smack the plug all of a sudden?