I owned a 400/4 back in 1977/78, but sold it to buy a GS550 E…never regretted it. The 550 was superior in every department…no dispute there. It’s not that I didn’t like the 400/4 and I had lots of fun on it, including a dawn fast lap round the IOM TT circuit, which was a real eye opener. The same year I bought the 550 I Chanced upon a bloke in Blyth, near Newcastle riding a tuned 400. I seem to recall it was called a ‘Mohawk’ (mocheck maybe?) or something similar. It was tuned to the bollocks: big bore, cam, exhaust, modified airbox, head job and raised compression. Anyway after his 30min self promotional lecture on the benefits and wisdom of the investment, I suggested we might test it, purely for scientific reasons you understand. It couldn’t get near the GS and after about 15 miles or so I’d lost sight of him in the mirrors. Out of concern I turned round to check the situation out. The bloke was heartbroken as the bike had dropped a rod and there was a massive hole in the crankcase and sump. Maybe he’s on this forum?