Fouled plugs on 1990 Johnson 200hp

[Iceboy149]

So I got her out 3 times the past three weekends and you guys were right, my 20' flew with the 200hp old Johnson. But here's the thing, I think I keep fouling plugs. THe first time I got her up to 5200rpms she flew and then I backed it down and then she wouldn't go over 3300rpms in gear but in idle she would go to 5300. Then I put all new plugs in as the old ones did look dirty and fouled, all of them. Again back up to 5100rpms this time but this time for about 30 minutes and then the same thing but limping back to the dock at 4200rpms. But now the brand new plugs all look the same (black but not necessarily fouled). And again out of gear she'll go to 5500rpms. So Since this motor sat face down all winter in the garage could this be the result of carbon/oil/general gunk buildup getting flushed through the system?
I took the cover off the carbs and they they look perfect but right where I think the fuel gets injected above the bowl there's a tiny bit of black gunge buildup.
By the way, all the fuel lines, tank, fuel water seperator, everything is brand new except for the motor itself so I know it's getting clean fuel.

Should I just keep popping plugs in her with some additives?

Can it eventually work itself out? Or should I have someone go through and clean up the carbs. Or will the ethanol fuel just keep cleaning the system til its done?

Thanks again fellas.

[Fr. Frank]

But now the brand new plugs all look the same (black but not necessarily fouled). And again out of gear she'll go to 5500rpms...
... above the bowl there's a tiny bit of black gunge buildup.
By the way, all the fuel lines, tank, fuel water seperator, everything is brand new except for the motor itself so I know it's getting clean fuel.
... should I have someone go through and clean up the carbs.
Or will the ethanol fuel just keep cleaning the system til its done?...

If this is a looper engine, I suspect electrical fault may be a possibility. But definitely clean your carbs and rebuild and clean your fuel pump as that may be all it is. They're not difficult to do yourself on that motor.

I had an '88 225 Johnson on my 23' Tsunami that ran great, but would end up limping back to the dock. Had the carbs cleaned, VRO pump replaced, new fuel line, filters, everything. It turned out to be the stator assembly, with a temperature hidden fault that only showed up when the stator assembly got hot. Cost back in '06 was about $900 what with all the time tracing down the problem. I bought a blown motor on ebay, got the used stator assembly off and the problem was fixed. I spent less on the blown motor than the cost of a new stator.

BTW, the ethanol fuel is not good long-term for your system. According to a friend of mine who is a Merc dealer, more than half of all repairs he is now performing are because of ethanol-related failure or damage. He says the first motors actually designed to run ethanol fuel were the '07 and '08 models. Even my '06 Opti has rubber gaskets that will deteriorate rapidly.

[Bushwacker]

The plug fouling problem you're having most likely signals a weak ignition. Had the same thing happen on my old 1975 V-4 when power pack was going out. It was a magneto type CD system with single power pack. Put in fresh plugs in Green Turtle Cay, Bahamas just before return trip. Put it on plane and stayed there for about 4 hrs, all the way to Mangrove Cay, where we stopped for lunch. As soon as I dropped off plane, it started running rough. Had lost both cylinders on one bank. Changed those 2 plugs, put it back on plane, and ran on to West End where I installed spare power pack and changed those same 2 plugs. (once they're fouled, they won't fire, even with new power pack!)

Suggest you make up a simple spark checker which will check entire ignition system in about 5 seconds! Got the idea from a tool in the OMC manual. Gather materials as follows:
1. Large PVC cap (I used 2.5" for my V-4; probably should go larger for V-6)
2. Seven 1/4-20 SS machine screws, approx. 3" long; could be shorter for a V-4.
3. One 1/4-20 nut.
4. ~1' length of 12-14 ga solid copper wire with alligator clip on one end.
5. Adult beverage of choice.

Drill hole in center of cap, tap for a 1/4-20 thread. Spray inside of cap with flat black paint. Thread a screw into cap with a ground wire under screw head on outside of cap. This will be your ground electrode extending inside the length of the cap; I used the heavy solid wire because it helps support cap on engine. Now install 6 more equally spaced threaded holes around circumference of cap, pointing at the center electrode. Holes should be about 1/2" from end of cap. Cut the heads off the remaining 6 screws and install in cap. Use the nut to set a 7/16" gap between each radial screw and center electrode. Need to have at least 1.25" of threads sticking out of cap. Can also use a nut on each stud to lock it's position/gap in cap.

To use, simply connect a plug lead to each of the 6 "studs" and attach center electrode wire to a good ground on engine. I used the lifting ring attached to top of block on my V-4. If boat is not in water, hook up flushing attachment and turn on water. (Never even crank the engine with a dry water pump if you want good life from the pump!) Now have an assistant crank the engine (or turn on ignition and use a remote starter switch to jump solenoid) and watch for a spark between each of the 6 studs and center electrode. (Keep your hands away from cap during this test! A healthy system puts out about 40,000 volts!) If no spark at one or more wires, start checking for tight connections, bad coils, bad power pack, or bad sensor or charge coils in stator assembly. Now celebrate finding the problem by enjoying adult beverage!

Like Fr. Frank, I bought the entire ignition system off a blown motor and carried the parts as spares on my Bahama trips. The spec in the OMC book called for a 7/16 gap, but a healthy system should jump a 1/2" gap. The black paint inside cap makes it easier to see the sparks in bright sunlight! Enjoy! Denny

[fdheld34]

Wow what great above guidance!!
Speaking of ethanol.......
I searched the internet and found tons of additives for fuel to combat ethanol!!. What is the best additive to use if needed??? or if routine maintenance is done are additives necessary??
Fred

[castalot]

i like StarTron (sp)? also johnsons only like champion plugs for what ever reason

[Iceboy149]

Wow, thanks guys. I never would of come up with that. And thanks for spending the time to write it all out.

I'll be doing it this weekend.

Awesome, thank you again.

Dave

[eggsuckindog]

The first thing to do with that Johnson is de-carb it, especially if its had weak ignition issues. Use Deep Creep available at Napa or any auto store. Just read the instructions after warming it up and spray the crap out of that stuff. It will also clean the plugs at the same time, so maybe throw both sets in while you wait the 15 minutes and clean them up too.