TO-30 Plug Gap?

If you run well with a wider gap it generally means that your ignition system can provide the higher voltage to make the spark under the fuel/air charge conditions in the cylinder. Have you checked your compression? It"s easier for the spark to jump a gap at lower pressures.

After running for a while, pull a plug or two and see what the insulator looks like around the tip. That might give you a clue.

If your idle mix screw is too lean your TO will idle poorly up to ~400-500 rpms before the power mix screw takes over. Over 400-500 rpms the mix is all controlled by the big "power" mixture screw.

In general the wider the gap the better the combustion... right up to the point that the spark can no longer jump the gap.
If your TO likes .3" gap, and runs strong, run it that way and work it!

George

I use Champion D21, which is a hot plug in my 1957 TO-35 gapped at .025-.027, runs good on them. The 1957 TO-35 has a 12 volt system, do not know if that makes a difference.

I have not found any plug that last like the olds one's did back in the 60's.

You can drop the plows and little Fergy will bellow with these plugs, runs like a top for a 50+ year old tractor.

I buy the Champion D21's at local NAPA store, they seam to have a lot of parts for the older tractors. Their technicans recommended the plug to me as we have to turn up the fuel a bit (open power screw) when doing heavy work and the richer mixture would kill the plugs faster. These plugs last longer for me.

Good luck with your tractor.