Why 2 cycle motor continuously foul spark plugs?

Question

early 1990 evinrude, gradually started fouling plugs months to weeks now every use. I have to change every use now. Runs great all day after motor sits for just 1 week I have to change plugs again. premixed gas and oil ratio correct to manufacture 50:1. recently rebuilt 4 yrs ago. used weekly. rebuilt due to oil pump failure, now premixed. start on first try with new plug.

Answer 1

make sure the fuel/ oil  mixture is correct 50:1 like you said, and rebuild the carbs thats probably all your problem is

Answer 2

Two possable reason I can think of:

Worn out rings/valve seats.  Major rebuild.

Coil not putting out proper voltage.  Check magneto clearance from flywheel and all wiring.  Might be time for a new plug wire or something real simple.

Answer 3

The mixture is too rich. Overhaul carb.

Answer 4

i would try a differ ant brand plug, after placing injector cleaner in fuel as well , check you have a ideal temperature plug.... it might be needing a colder plug. check out the sales catalogue on plugs.