Open-air spark tester arc length for Johnson 85hp 1974?

[kippstakes]

Getting ready to test compression and spark on my new, used, engine tomorrow. How far should the arc be able to jump on an open-air tester?
Thanks

 

[SilverSS07]

From everything I've read 7/16 inch

 

[kbait]

I've always tested by the following:
Points ignition - 1/4" snappy blue spark. CD (electronic ignition) - 3/8" in open air.

Both ignition types will likely arc more than that, but those distances will be adequate for proper spark across the plug gap under compression.

Good luck!

 

[kippstakes]

Perfect. Thanks for the quick replies!