Did some quick research, several sources.. some misinfo out there..
A 1930 Four has weights listed as 385, 455, 460 lbs.. so I am inclined to think it is in the latter range..
Which is not really bad for a 1280cc motorcyle... sounds a bit like a superbike to me.. The fours porked up a bit through the 30s and by 1940 with the plunger frame/full fenders was up to 560 ish..
I posted this thread due to another incedence on here of Harleys(and other American ride) must be heavy..
Yeah Frank, I found this online myself:
"a 1928 4 would weigh about 455 lb, a 1942 model ( the last year of manufacture) weighs 568 lb."
I think the 31 was before the full skirted fenders though, I don't remember, but of course the '42 at 568lbs, has the full fenders & plunger rear suspension, as mentioned. Here's a shot of the 1928 model, which weighs in at 455 lbs
I haven't found a shot of the 1931 yet, but I'm still looking, though I imagine that it looks similar to the '28.