The short answer is no, there are no roads leading into PNG from Irian Jaya, it is a rather sensative border re Indonesia's annexation of Irian Jaya and the internal strife that accompanies such a regime.
As for travelling in PNG you are limited to the only road network and I use the term loosely is from Lae to Mt. Hagen and currently one of the bridges has collapsed so vehicle traffic is very limited at the moment.
The only road network out of Port Moresby is up to the Kokoda Track (20 Miles) just be careful of 'Rascols' (criminals). PNG is a very bueatiful country to visit but has no road network to speak of so as for a motorcycle adventure it is some what limited, as an adventure in itself it has that in spades.
Without adventure life is in full decay.
Macca & Lynda