Spark Plug Conversions

[Rich Peterson <kerry3@earthlink.net>]

I'd like to replace the Champion plugs in my '77B with some NGKs and
would like some advice from the list.  The Champions seem to cross out
to two heat ranges in the NGK plug.  Which should I use -  the hotter or
the colder?  I'm inclined to go with the hotter of the two since I tend
to do a lot of city driving and build up a lot of carbon - the ZS carb
doesn't help much here, either . . .

What do you think?

TIA

Rich P.