fouling on plugs

1990 force 120
I have to keep cleaning plugs after each trip to the lake. I didnt do it once and it left me sitting a few miles from the marina and had to be towed back. The carbon builds up, but you can pull them and scrape it off with your fingernail, pop it back in and off you go. Now I have added a sparkplug wrench to my boat box. I wonder if its a mixture thing or idle setting? If I try to troll slowly the engine dies. If I try to switch from reverse to forward without a few seconds pause, it dies. Added a temp gauge to the head and it stays at 138-142 degrees.

Re: fouling on plugs

Hmmm maybe the thermostat is stuck open and engine is running a tad on the cool side. Is this motor pre-mix or oil injection? Also check your plug type in your manual. The plugs may be running a bit on the cold side. And have you always had this issue? You may very well have too rich of and idle setting.

Re: fouling on plugs

sutor623 said:

Hmmm maybe the thermostat is stuck open and engine is running a tad on the cool side. Is this motor pre-mix or oil injection? Also check your plug type in your manual. The plugs may be running a bit on the cold side. And have you always had this issue? You may very well have too rich of and idle setting.

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It is 2 cycle pre mix. Thermo is not stuck. It opens and closes in a pot of hot water. It is a 143 degree thermo, so it is holding around the right temp. I dont know about plugs, I dont have a manual. I havent had the boat long. It had new plugs when I got the boat. It ran good the first trip out and died on the second after a good hour. When it died it wouldnt hit a lick, just spin spin spin. It did backfire two times. Thats when I learned to clean the plugs. Ive had it out several more times and it has done very well, but towards the end of the day it gets a little cranky at low rpm and shifting. Once the plugs are scraped off its good to go.

Am I in danger of fouling something else in the engine that I cant scrape with my thumbnail?

Re: fouling on plugs

At the top of the postings is a FAQ sticky. In there you will find a Link and Sync procedure. You need to do this, as it sounds like the air screws are out of adjustment. Or you are mixing heavier than 50:1. Both air screws should be roughly 1- 1 1/16 turn out from lightly seated

Re: fouling on plugs

This is a common problem with Force engines. So common that I always carry an extra set of plugs. If a fellow Force owner is having problems starting I hand him a set of clean plugs and usually---off he goes.

Because these engines are 50-1 premix and not oil injected, there is way more oil than needed at idle. Extended slow speed running or idling will usually result in fouled plugs.

Plugs can be cleaned and reused indefinitely. I use a piece of a green Skotchbrite pad to get out the carbon and oil. My kit includes a couple of Skotchbrite pieces, a plug wrench, and at least one set of clean plugs. Incidentally: on the 125 in this photo, I have never experienced plug fouling or hard starting---but this engine always runs at 5900 RPM, full throttle. The only time it idles is in the no-wake zone around the launch ramp.

Back to your engine: If the idle is not 700-750, in forward gear in the water, with a new set of plugs, then using the idle stop screw on the tower, raise it to that. The lower unit should make a definite "clunk" when put into gear but it should not be harsh or excessive.

Fouled plugs will lower the idle speed so when she starts to stall when put into gear--change'em.

If you intend to do a lot of trolling, either mount on a kicker engine or carry a six gallon tank of premixed fuel at about 75-1 ratio just for trolling.

Re: fouling on plugs

Frank I bet that boat you've got there does 50MPH!

Re: fouling on plugs

Ahhh--that boat tops out at 60. With the 90 in the photo, it goes 55.

Re: fouling on plugs

Do I need to do the adjustments in the Sticky? I tried to read through it. Whats the cam that we are unhooking? I went and got new plugs and a plug wrench (chainsaw style wrench)to keep in the drybox and a green scotch pad. Also can you give me a better idea of the idle screw location. Is it right under the flywheel or low on the vertical rod beside the carbs pushing against the block? If the adjustments on the carbs need to be done, is that all done on the water? Tied to a pier or find a quiet cove?

Re: fouling on plugs

Idle screw is low on the vertical tower shaft. It should have a lock nut to prevent it from moving. Initial carb adjustments can be done at home, with fine tuning done on the water. Testing on the water is always the best way to confirm that everything is set right.

Re: fouling on plugs

Also, to touch back on over mixing the fuel, the oil goes in with the gas and I added a can of seafoam. Im going to add Sta-bil Ethanol treatment next time I fill up. These addatives are not contributing to the problem are they?

Re: fouling on plugs

Probably not, but just for testing, just get a small external tank of gas without any additives and try it.

Re: fouling on plugs

I have not messed with the carbs yet just to help with not confusing the process of elimination by doing too many things at once. I added ethanol treatment in the last tank along with trying a new oil. Instead of the regular marine 2cycle oil I used a synthetic that said it was for older outboard engines and would help reduce fouling and carbon build up. After a extra long time trolling around I was waiting on the engine to die. I had the scotchbrite pads and a wrench ready. I couldnt belive I was still going. When I got home I pulled the plugs and simply wiped the oil off the plugs with a piece of cloth. No effort required. The oil did as advertised, there were a few black speckles on the plug instead of the whole thing looking black and crusty. The idle seemed to be around 700-750 at an idle while in gear and around 1000 out of gear. I still might need to go through the carbs though. While trolling if I tried to keep it around 800 rpms it would jump up to 1100 for a while then drop back down. It was not just the tach dancing around because you could hear the engine anf feel that you were going a little faster. If I tried to pull it back down when it jumped to 1100 to keep it at 800 it would stay for a while then drop to about 600 for a few seconds and die. raise the throttle and turn the key and it fired right back up. Any ideas on that?

Re: fouling on plugs

Maybe fuel pump diaphragm, or if you have the older style fuel pump that kind of looks like a figure "8", there's three check valves that are known to stick.

Fuel recirculation system. At low speeds, the fuel tends to puddle up in the motor and the fuel recirculation system is designed to bleed this excess fuel off and burn it up. There are some small hoses and check valves that can get plugged up with crud and prevent it from working. A shot of carburetor cleaner usually solves that problem.

Make sure all the bolts and gaskets on the carburetor adapter plates are not leaking and snugged down tight to prevent any vacuum leaks. I believe there are 8 bolts on each adapter plate that the carburetor is mounted to.

Note: I've switched to 100% synthetic and seems to do better too. Very little fouling on the plugs. Still trying to convince my wife it's worth the additional cost. LOL!