Spark plugs

[Fereday]

Hello again just a quickly . I've run my thunderbolt on champion nc3 plugs for about 100 miles and the wright hand side seems to be breaking down what plug would be suitable. Thanks

[JulianS]

N4 was listed up to 1968 then  N3/NC3.

But NC3 should be OK. Its just a slightly colder plug.

If the electrode or insulation is breaking down then its getting much too hot and there is a problem which needs sorting - over advanced timing or too weak mixture being possibilities.

[STAR TWIN]

My bikes have never got on wel with Champion plugs. Try NGK B7ES.

[TTJOHN]

The book states N4 plugs for the Thunderbolt, with resistive HT lead.

Regards TTJohn