1985 Mercury 150hp Black Max plugs foul every tank

[mtndew]

I have a 1985 Ranger 350-V with a 1985 Mercury 150hp Black Max which is new to me. When I purchased the boat I was told that there might be some bad gas in the 6 gal tank. (It has 2 tanks, 1-14 gal and 1-6 gal) the other tank was empty. Took it to the lake and it was hard to start and would not idle. Got home and pulled the plugs and they were solid black. Cleaned them, replaced them and everything seemed good. Ran new non-ethanol premium gas @ 50-1 mix and a can of seafoam. Ran ok but still fouled the plugs. Bought new plugs and installed them and then I messed up. I thought I was filling up the 14 gal tank so I poured a quart of oil in the tank before I filled it up. I was filling up the 6 gal tank and had put too much oil in the tank. Filled up the other tank correctly and went to the lake. Ran better but when I pulled the plugs still fouled. Pumped the fuel from the 6 gal tank into the 14 gal tank and filled it up with non-ethanol gas again. Pulled the plugs this morning and fouled again. Clean them, replaced them and put the muffs on the motor. Starts right up, purrs like a kitten but I know the plugs are going to be fouled when I run it all day. Side note: She absolutely screams across the water, she just doesn't want to start easily or idle!
Any ideas or suggestions?
Please!

 

[Chris1956]

You have another issue. Fouled plugs are a symptom. That motor will run just fine with a 25::1 fuel mix.

Check the fuel pump diagram for a tear. Check the carb floats for flooding. Check the spark quality.

 

[mtndew]

Is this something that I can do myself? My mechanical skills are limited to changing plugs and checking resistance on powerpacks.

 

[Chris1956]

A spark tester will tell you if you have good spark. The spark should jump a 5/16" gap.

Alternatively, take a spark plug out and install it into a spark plug wire and hold the base to the block. When the motor cranks, you will hear a loud snap as the spark jumps the gap.

Test all 6 cylinders. All should have a snappy spark.

Pump the primer bulb and look at the carbs and see if you see any dripping into the engine (down the carb throats) or into the cowling. If you see leakage, the carbs need rebuilding. that may be beyond your ability.

The fuel pump is easy to rebuild. It has a diagram that keeps fuel from leaking into the cylinders, bypassing the carbs. If the diagram tears, the motor can flood.

 

[mtndew]

I don't know if this changes anything but after I clean the plugs she starts on the first try, idles smoothly and runs like a champ. It is only after running and gunning all day that the problem with the plugs begins to show.

 

[Faztbullet]

A fuel pump tear will not foul all 6 plugs...Engine running to cool, carb floats heavy or recirc valves stopped up.

 

[mtndew]

How can I check that?

 

[Faztbullet]

Go to boatinfo dot no and get the manual then test t-stats and recir valves. Carb will need removed to check floats