Originally Posted by solarguy

Thanks for the info but I wonder what plugs are the guys with 340’s actually using?


Autolite 63 on my 340 runs great [/quote]

65 is the OE replacement. As the number get smaller, they get colder. We ran 55-51 back in the day. Same plug, nonresistor. Many of these numbers are NA. 63, 64 and 65 are still good.

If the results don't match the theory, change the theory.