engine temp.

ive got a 71 std. beetle 1600 dp manual trans.
im having a problem with the rubber isolator going into the dist.
melting.
i've determined that its melting from the outside(wires are not blackish,
still look like new copper)
it seems to be cooling ok, or at least the fan is blowing strong.
im wondering if the thermostat could have anything to do with this or if
maybe carb. adjustment or timing could be the cause
the car runs great untill the rubber melts and the wire inside grounds out
stopping spark.
it has a bosch coil, the dist. is original except for points and cond. the
rest of the ignition system is aftermarket.
thanks in advance for any replies
matt