Morris Minor Owners Club

Could anyone out there help me with this issue....

I have a bit on an issue whenever I touch an SU Carb. I seem to have de-tuned the one on my saloon and the pair on my Spitfire. What's annoying is that, if I've understood the bits I've read on line, the only bits that you can adjust are the mixture nut and the idle screw. So what am I doing wrong..!!???? It's driving me to distraction, especially on the Spitfire that sometimes runs nice and others not...

All and any help very much appreciated...

On the single - yes all you can adjust is the idle - the fast idle (when choke pulled) and the idle mixture settings. Make sure the throttle cable and the choke cable are free running - and have slight slack when closed. Then just set up as you wish! Other variables are the strength of the spring in the dashpot - the grade of oil in the dashpot - and of course the needle in the piston. Fuel level in the float chamber can be varied too - but isn't normally an issue.
On the twins - as above really - but do disconnect the joining link on the throttles and make sure each carb is free to return to the idle stop. I only ever use one 'choke' (actually - cold start enrichment device - it's not a 'choke' at all!) when running twins - saves linkage problems and still starts up just fine. Set the idle by listening to each carb with a rubber tube to your ear - and the other end held in the SAME spot at each carb entry - adjust the individual idle screws until both 'hiss' the same. Then carefully lock up the joining link without moving either carb spindle - and minimise the 'free play' in the joining link - there is often a fork/bar arrangement - set it as close as possible so the carbs open exactly together. Mixtures are set in the usual fashion - and test by using the lift pin until both carbs respond equally. Check by inspecting plug colours after a good road run. The carbs should 'never' go out of tune if set properly in the first place - that's a myth!