1993 Johnson 120 HP

[nujac]

After boat has been stored about 2 weeks, on start up, it idles and runs poorly. More importantly, the motor "bogs" down and can not go to full power or develop appropriate RPM for some time. I usually have to keep going from full power to idle, then going back to full power. At some point, whatever is causing the motor to not reach full power, starts to clear. Then it will "catch" and then runs very well throughout the day. This will occur again if I do not run the motor for about 2 weeks to a month. Even though it starts on the driveway, smokes very much and I run it at 800-1200 RPM, upon putting it on the water and trying to go to full power, the same problem occurs until again whatever is preventing full power, clears and then it runs well.

Repair shop changed plugs, cleaned coils and said the idle and high speed jets were ok. However two weeks after this shop visit, the same thing happened. I have since changed the fuel filter as well as the water separator filter. The problem continues.

Any suggestions would be appreciated.

 

[boobie]

Is the VRO still hooked up ??

 

[Cap'nHandy]

Sounds like fuel issues. Mine acted the same way till the carb got rebuilt. To test - Disconnect from tank, and run off a small batch of fresh gas. If it is still doggy, carbs likely need cleaning. If that cures it, then drain the tank and refill with fresh before you go out.

Unless the shop tore the barbs apart, I dont know how they could see if the jets were truly clean. Fuels with ethanol go to crapola in short order, and make for all kinfs of problems.

I mentioned in another post to use some "Mechanic in a bottle". Recommended to me by my brother, who is the Chemist for VP Racing fuels. Cleans varnish like you would not believe. Use a small bottle that is good for 4 gallons, in a gallon of fuel Run it a little while, till you know the fuel in in the carbs, then shut it down and let sit overnight. Next day run it again till you have gone through half - then again overnight. Next day, run the rest out. Should take care of any varnish issues. Of course, tearing the carbs apart and doing a real job on em is best. Make sure to decarb - and check you have good compression.

Blaine.

 

[nujac]

The VRO was removed some years ago as recommended by my mechanic. Since then, I add oil to the fuel (50:1) and also include an additive made for Johnson/evinrude motors. What is baffling is this occurs during the initial start up and after running for a while. As indicated, at some point, whatever is preventing the application of full power, somehow clears and then it runs well usually for the rest of the day. I do notice even at idle, he motor was not running rough. I suspect it could be clogged jets and then somehow they clear, but not sure.

 

[Cap'nHandy]

On 2 stroke outboard motors, the most common problems are fuel related.
A common weak point is the power packs.

If your gonna replace / fix parts, start with the least expensive fixes first, and use methodical troubleshooting.

Here is my thought process.

Since most common is fuel related - AND you should do this every so often anyway, your highest likelyhood of success is here. if your wrong, no harm, no foul.

----- Plan of attack --- What I would do if it were mine. --

GAS check. run it off a small tank. if problem goes away, drain tank refill with fresh and something to deal with water.

If problem remains, - do the carbs. Use the previously mentioned "mechanic in a bottle". Its very good. Like I said, The Chemist for VP Fuels (my younger brother) told me how it works. He is a true subject matter expert on fuels. Not "snake oil" VP now markets this - and they have a reputation to maintain.
For $4 or so, it would be much easier than pulling the carbs. But DONT just dump it in the tank, cause if your fuel is bad, it will be too dilute. The small bottle that treats 4 gallons would be enough, but get some full strength or in a gallon of gas and oil - into the carbs, and let it set overnight. Directions on the bottle. Let time and concentrated cleaner do the work to dissolve the varnish. Failing that, just pull the carbs - its not hard. If your doing this, may as well replace all fuel lines.

Decarb the engine and replace the plugs.

If the carb cleaning does not do it, then it may be related to the power pack or coils, or other electrical.

For electrical, corrosion is a problem due to environment. First, and cheapest is to clean and reseat all connections and plugs. Thats one step you can do easy.

Then you get into testing with a DMM or VOM and DVA. After those tests - you may end up replacing the power pack or other parts.

But dont rule out fuel. Mine acted the same way. Carbs clean / rework did the trick.

Most important in problem solving is not to half heartedly jump around from item to item and hope to get lucky or think it will just solve itself if you run it enough.

Good luck.

Blaine

 

[nujac]

Thanks Blaine for the additional information. I'll start with the Mechanics in a Bottle and clean fuel to see if that resolves the problem.