Spark Plug question

[opposedtwin]

How often do you guys change your plugs on your frequent runners?

My most frequent runner (1957 FD-11 18 hp) gave me alot of trouble the other night. It has run like a swiss watch for 2 full summers and for 3 or 4 outings this spring. Then one afternoon at wot (which is the normal running speed) the rpms were jumping up and down and then finally it wouldn’t get all the way up to full rpms at all. I limped it into the put in and took it home. Today i checked compression (110 top/bottom-i re-ringed it about 5 years ago). Also had good spark in both cylinders. When i pulled the plugs they were pretty wet and fouled. These plugs have a full season on them from last summer. The low speed needle was pretty loose so i added a piece of packing to both needles and they are good now. Put in new plugs and it started and ran in a test tank but I won’t know for sure if that’s all it was until i test it again on the lake.

I have been using nos champion j6j plugs. What is a modern replacement for them? I am now out of them.

Also, anything jump out at you as to what might be the problem based on the symptoms I mentioned?

Thanks for any input.
Scott

[wedgie]

J6C is the new Champion plug. Some folks swear by the NGK B6s, and I have had good results with them too.

[frankr]

You got two + seasons out of them. I’d call that pretty good. Put some new J6C’s in it and adjust the carb and see how it goes. You might have to go in and check the breaker points.

[outbdnut2]

On a 25 to 1 gas/oil mix motor, expect to clean spark plugs occasionally. A spark plug wrench came with new Johnson’s back in the late 1950s/early 1960s. If you went two summers and used it much, you did very well without cleaning the plugs. Yeah NGKs seem to be a bit better in a lot of motors, but I’ve not seen a problem with Champions in your model.
Dave

[Author]

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