Champion J11 may not be the original heat range so a
“J” type in a different number may be what is called for. A compact
version of “J” may be needed if a spark plug cover is involved.
Spark plugs were made to sell under various store brands which mau be hard to find. Spark plugs are standardized. so far as physically fitting engine. A little comparison will verify which of the several standard size
Good Luck
edit
Spark outside cylinder but,, not under cylinder pressure is likely a low
voltage issue…it take higher voltage to jump gap in compressed air in
cylinder than in open air. Coils can have an internal short or ignition
lead insulation deteriorated or damage. the spark will jump gap or
spark plug in open air ,but, find the short an easier pathe when spark
plug is under cylinder pressure at or near TDC.
All I know about magnetos on old outboards is that they come covered
with crud. First you remove the crud. That seldom makes them work,
but, you have to start somewhere.
Try a spark plug that is known to work on another engine. Spark plugs, even new ones can be defective. Same for condenser.
I once almost pulled my arm off trying to start a snowblower with a new
spark plug of correct specification. On a hunch I put the old spark plug back in and it started with 1 pull. Go Figure. It generally is a good idea to install new spark plug before start of season for either lawn mower or snow blower…maybe so, but, don’t pitch the old spark plug until the new one is up and running.
Good Luck
