Spark Plug Compatibility

[StickyWidget]

1976 75HP Evinrude

New to me engine with NGK BP78HS-10 spark plugs installed.

Marina suggested Champion QL77JC4 plugs. (They cross referenced it in a book)

I put them in and the engine wouldn't even barely fire.

I did a search and found that the QL78YC is the proper plug. Put them in and the engine run like it did with the original NGK plugs.

Since swapping plugs I found a label that suggested Champion L77J4 or AC M40FFX on the engine.

I couldn't find a match to the L77J4 but the M40FFX does match the QL77JC4 which didn't really work in the engine.

The plugs do jump a 7/16 inch gap. The best I could figure is one plug has a projected tip and the other did not.

The engine is running (with some issues) with the projected tip plugs (QL78YC).

Any reason why the engine would not run with the recommended plugs?

The gap was set at .030 on all of these plugs. I have since got a CLYMER manual that states .040 gap.

Could that have been the issue with the recommended plugs?

Will the current plugs hurt my engine?

 

[orbanp]

Re: Spark Plug Compatibility

There is a factory Spark Plug Chart for Johnson and Evinrude outboards on the BoatSetup.com web-site.
It lists Champoin L77JC4 or QL77JC4 plugs for your motor gapped at .030".
Wrong plugs does not hurt the motor except the motor might not run perfectly (assuming the plugs do not disintegrate in the motor ;-)

Peter

 

[kenmyfam]

Re: Spark Plug Compatibility

Stick with the recommended plugs gapped between 0.030" and 0.040"
If you still have running issues you need to troubleshoot for the root cause elsewhere.