Plug Gap 1990 Johnson 30 HP

[Johnnielund]

I have a 1990 Johnson 30 hp m

I have a 1990 Johnson 30 hp motor. According to the OMC service manual the recommended spark plugs should be either QL77JC4 or L77JC4 gapped at .030.
After speaking with Bombardier tech support I was told that QL82JC4 gapped at .030 should be used if there would be extended idling. I have also heard from some OMC techs that the gap should be .040. Bombardier says they have no technical bulletin reflecting the change from .030 to .040. Can anyone offer some information on the proper gap and why?

 

[jupiterzeke]

" Johnnielund;My 2003 Bombardi

" Johnnielund;My 2003 Bombardier Dealer P&A Catalogue says to use QL77JC4 orQL82C gapped at .030 or L78V surface gap.A gap of .030 will usually cause the plug to last a little longer.I've been working on John/Rude's since the 1950's and the plug gap has been .030.For general use on mid-grade gas and GOOD oil I recommend Champion L77JC4 at .030,The "Q" is for radio suppression only if needed.
jupiterzeke "

 

[joereeves]

"Johnnie... The s/plug gap sin

"Johnnie... The s/plug gap since 1973 when the Magneto Capacitance Discharge ignition came into existence was recommended to be .040 . The general s/plug was/is either the Champion QL77JC4 or the L77JC4, the heat range being "77".

That same type ignition exists today, but I know that some models in later years have been switched to the hotter QL82JC4 (heat range "82") being set at .030. I can only assume that the associated engines have a tendency to foul the "77" s/plugs, hence the hotter plug "82" was/is recommended.

I've come across a few engines whereas even the "82" plug had a tendency to foul, and widening the gap to .040 cured that problem. Rest assured that you can widen the gap to .040 and encounter no trouble/problems.

Some problems, unfortunately, regardless of what it may state in a service manual, still fall back on the trial and error scenario... the end result of which is what usually results in the well known service bulletin.

Bottom line... try the QL82JC4 plugs set at .030 and .040, then try the QL77JC4 plugs set at .040, then use what works best for you. Sorry not to have a definite answer. Good Luck..

Joe

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