Rick;

Elaborate on "dreadful"!...are one or more cylinders not firing (I would describe that as dreadful), until heat of engine compartment comes up, and dries things out a bit, or what?

Just yesterday, during cold, drizzly, winter-is-just-around-the-corner-weather, I brought a 122 which has been parked for a couple of months now (for not starting during a rain storm) back to life...when cranking, it was showing zero signs of firing...so I started by just wiping clean the condensate from surfaces under the dist cap...then I double checked if the choke was giving enough action at the jets (I like to see abou 1/4" of lowering) and tried again...voila! Bottom line: Keep ignition components, especially under the dist cap, clean...clean means no high voltage discharge path when moiture starts condensing on surfaces. It's the simplest thing, but crutial.

The "thunk" problem needs further explaination also...are you discribing a lean backfire?

Cheers