Spark Plugs on Evinrude 9.9/15 hp.

[driver0606]

Hello. My 9.9 Evinrude with 15hp carb has NGK B5HS plugs.My local agent says these are 2 stages too hot and could burn holes in the pistons at high power. I have ordered the correct Champion QL77JC4. Has anybody any experience of this problem with plugs that are too hot?

 

[Vic.S]

Yes they are 2 grades too hot. If you must or prefer to use NGK plugs use B7HS (or B7HS-10), or preferably BZ7HS-10 which are the equivalent of QL77JC4

What ever you do do not use resistor plugs, eg BR7HS-10, often listed and sold as equivalents of the Champion Q series.

( By the way -10 on the NGK number indicates that it is supplied gapped at 1.0mm otherwise the same plug as one without -10)

 

[driver0606]

Thanks for the confirmation. Is there a risk of burning a hole in a piston if using these plugs while awaiting the replacements?

 

[ondarvr]

Thanks for the confirmation. Is there a risk of burning a hole in a piston if using these plugs while awaiting the replacements?

Yes

 

[oldboat1]

agree^^. (can't let you do that right after getting that carb mounted and adjusted :faint2:.)

thinking you may be trying to get higher performance using the hotter plugs in combination with the larger carb. Along with avoiding damage with those high heat range plugs, might want to keep everything stock until you can get a sense of whether the carb change alone makes a difference. Keep the fuel mix at 50:1. (JMO)

 

[driver0606]

Thanks. All advice noted and taken. Hello again Oldboat1. Actually these plugs were fitted by a local outboard repairer, (but not Evinrude agent). Shows you need to stay with the real specialists. I have run it at maximum for a few short tests (2 to 3 minutes a time) with these hot plugs and am keeping my fingers crossed that I have not already done any damage!.

 

[racerone]

Just as important or even more important is to make sure the cooling system is in tip top shape.-A hot motor will still have difficulty in getting rid of heat from colder plugs.