I've had to largely guess at setting up my 1993 1.1 carb metro and seem to be getting better at it. However, today I went to a local junk fair and picked up a good Draper timing light and a Gunson Tuning multimeter together for £5. I then used the timing light and tacho function on the meter to correctly set the ignition timing to 9 degrees - it was way off the scale at nearly 16 degrees. This had an effect on my guessed settings and so I set the torx diaphragm air bypass screw to half way along its travel of 6 1/2 turns and set the jet screw to 2 1/2 turns in from the jet being at the same height as the bridge. Now, whilst the engine and exhause sound quite good like this, the idle simply isn't steady - it moves about +/- 50 rpm around the target of 850. Any ideas?

Did you check the timing with the vac disconnected, is the dizzy vac capsule good, ie doesn't leak?
get the CO checked and adjust the needle jet, check no leaks from the servo pipe, inlet manifold gasket is good,
is the coldstart/choke 'O' ring seals ok?
Try advancing the ign a couple of degrees, if everything is good, then a deviation of 50 rpm isn't bad for a carbed
engine.

Dave VVC wrote: ↑Thu Jun 22, 2017 7:21 pm Did you check the timing with the vac disconnected, is the dizzy vac capsule good, ie doesn't leak?
get the CO checked and adjust the needle jet, check no leaks from the servo pipe, inlet manifold gasket is good,
is the coldstart/choke 'O' ring seals ok?
Try advancing the ign a couple of degrees, if everything is good, then a deviation of 50 rpm isn't bad for a carbed
engine.

Thanks Dave - there's been progress since my last post and this is it. The lumpy idle was due to a weak mixture and I've found that my carb reacts best to having that recessed torx screw in the diaphragm housing screwed fully in. My diaphragm is new, and so does not leak. With this screw fully home, I can adjust my carb according to the usual SU rule of adjusting the mixture until the engine RPM just rises then falls back when lifing the piston 1/32". I am now happy with the idle, and it's much more stable but surely that screw should be out further as it has 6 1/2 turns out available. Any comments in respect of this screw welcome. As for now, I'll leave it alone and see if my plugs change from bleached white to brownish....