I owe you folks a huge apology and also many thanks for helping me understand whats going on/wrong with my 660.
I don't want to go on and on about something which isn't an MZ but sharing a common engine with the SZR was why I joined up here.
I've only used the bike for a few weeks and keen to sort out a few minor problems - the carburetion being one. I couldn't understand the engine breather system on my engine and thanks to edfmaniac and others I've got to the bottom of it.
A previous owner had joined the crankcase breather pipe directly to the secondary carb breather via the coarse filter barrel. When I disconnected the 2 parts of the pipe it was obvious that the engine breather pipe was just the right size to fit onto a stub on the airbox
I then reattached the carb breather pipe, with mesh filter, and let it dangle down the side of the engine.
Road test time and what a difference! I hadn't ridden a 660 before and used to twins. I thought the low/mid speed jerkyness was "characteristic" of the engine but in reality a PITA. It was never smooth when opening to full throttle quickly and was rough running below 3000 rpm in any gear. Now it picks up cleanly from just over 2000 and just about peaks at 7200 rpm in 5th. What a transformation! It also seamlessly goes from primary to secondary throttle on wide open throttle cleanly now, rather than fart, pop and rattle my bollox off the back of the tank!
Please ignore all the crap I was spewing previously about the carb feeding air from the crankcase, clearly not the case and it was through discussion and debate on here that helped me sort it
. Thanks very much. For anyone interested, here's some before and after pics.
Original plumbing, pipe from secondary carb connected via filter to crankcase
Original plumbing showing pipe down the back of the engine
Crankcase breather pipe now attached to the botton right of the airbox