Fouling Plugs

[brundag5]

I have a MY2000 90Hp Mercury Tracker that is fouling sparkplugs. The engine does not get used often and it is likely that the bad fuel has caused fueling problems.

Two weeks ago I removed the carburetors, took them appart and cleaned them. Surprisingly they were all very clean except for the #4 carb, it was slighty dirty. I removed all of old fuel and put in fresh along with carburetor cleaner. The engine seemed to be running well and no longer had the stumble when going to wide open throttle. However, it continued to run rough with minumum throttle with the drive engaged. Over this last weekend while out on the lake I was running the engine at 5000RPM and the motor cut back to ~3800 rpm. I took it back home and pulled the plugs. Number 2 and 4 were black / fouled out.

What are the potential causes of this? The floats did not seem to be adjustable, the fueling circuits are controlled by jets, so not much to adjust there. Could something be wrong with the choke? Thank you very much for any troubleshooting advice!

 

[Windykid]

Re: Fouling Plugs

Run a compression test.

do a spark test.

Decarb with sea foam.

 

[brundag5]

Re: Fouling Plugs

The compression test looks good as all cylinders are consistent and the spark looks strong on all cylinders. As for the carbon deposits, i'm not sure how that would cause overfueling. Possibly predetonation but not overfueling.

Has anyone out there had problems with there fueling system and been able to get to the root of the problem? Are these engines prone to this type of problem? I ordered a service manual, hopefully that will help.

Thanks for any feedback you have.

 

[jmburock]

Re: Fouling Plugs

I have had the same problems you described, de-carbing didn't do much except blacken/wet another pair of spark plugs. I think I need to rebuild my carbs to solve the problem- I am suspecting a float is not fully closing or too high resulting in the engine running rich.. However, better to run my 89 Mariner rich rather than lean...

 

[Vlad D Impeller]

Re: Fouling Plugs

Either its the carbs as you suspect, or it could be that the motor is not operating at the right temperature, check for a stuck on open thermostat.

 

[studlymandingo]

The stator has two windings.

The stator has two windings.

Check the stator with a DVA meter.​

 

[Evinrude6]

Re: Fouling Plugs

Check the mix screw on the carb- it could be too rich.

 

[lakemeadrat]

Re: Fouling Plugs

I just got a '07 Suntracker with a 90HP merc 4 stroke and noticed that the motor sets so low in the water at slow speeds that the exhaust water ports are below the water line. The manual says that doing this continually will foul plugs as well as other maladies. I'm trying to get some time to set it back in the water and take some pics to show the dealer. I don't know if the motor was installed too low or if it's no big deal. In the meantime I'm up&down or bugging my passengers to tell me when it's out of the water by adjusting the tilt. Don't know if this will help you but If ( or when ) I get any more info, I'll let you know.