I have a question? i have an 1975 85 hp Evenrude it keeps fouling out plugs pretty frequently i change them and it runs good for a while but then starts to miss again .any ideas ?

the plugs are fouling from fuel leaking past injectors and injector seals into the inlet manifold
it is nor a plug problem but injector and excess fuel problem as the fuel rail retains pressure when the ignition is off so any faults in the system will leak that pressure into the manifold

Do the basic checks:
Check air filter clean.
Check gas filter clean.
Check spark plug not fouled.
Check spark plug cables OK
Check fuel is correct grade/mix (50:1 for 2 stroke)

the next time it fouls check the plug when you take it out, if it is covered with oil then you may have a broken ring on the cylinder that is allowing oil to pass through to the combustion chamber and fouling the plug. Or the valves pay be letting oil drain in past the valve seats.

Hello jonbon742, if you haven't already, change your air filter. 75% of the time when people have the symtoms you do it is caused by the air filter.
Best of luck my friend!

If the insulator was cracked the plug would have been misfiring, unless it was broken while trying to remove it. If this oil fouling is an ongoing problem, and you have to keep changing the plug, buy a spark plug that is designed to fire when oil fouling is a problem. You may have to order one from a part catalog, such as JC Whitney. This would keep you going until you can get the problem repaired..

exposure to heat, weather,salt in winter and water make them more susceptible to failure I would change them knowing that my others failed

It's not usually the plugs that are the problem, it's the C.O.P (coil on plug) that go bad more frequently. Usually causes a pretty mean misfire, so you'll know when you have a problem. Otherwise just keep an eye out for the Check Engine light.

Now, about those spark plugs.........

If you do decide to change the spark plugs yourself, BE CAREFUL! They are recessed way down inside the cylinder head & have a tendancy to break in two when trying to remove. This is a major problem because then you can't it out without major disassembly. There are some special tools that help to keep this from happening that you can purchase at a good auto parts store...I would advise that you purchase these if you're going to tackle the job.

sounds like too rich of a mixture check for vacuum leaks and check fuel press regulator

24 mpg on the highway is actually pretty good for that truck. at 48000 miles and being 3 years old its time for plugs, air filter, and fuel filter if available. thats cheap maintenance for now. but if very self conscious, run some fuel injector cleaner first, then change the plugs, because any octane booster or fuel injector cleaner can run the risk of fouling out a plug, by creating a hotter spark then what, normal gas does. the burn is hotter.

Check your EGR valve or your EGR sensor. That will cause those kind of problems