[Healeys] Setting SU HD Carburettors

[Bob Spidell]

re: "In fact i have read in various publications the instruction that the butterfly must be closed at idle." 


Has anybody ever given an actual reason--theoretical or otherwise--for this proclamation? I've looked, and haven't found one (note your SU/HD manual specifically says otherwise, for multi-carb installations). 


re: "IMPORTANT: It is imperitive that the throttle linkage is allowing the butterflies to close completely. If not, it will not be possible to set the idle speed accurately'. " 


Well, apparently I've accomplished the impossible, as my BJ8 idles rock solid at 750RPM give-or-take a few RPM depending on conditions (altitude, temperature, etc.). I could go lower but I don't like to run off the battery, and higher idle RPM increases run-on. Moreover, the idle hasn't wavered in years, nor do I ever stall. 

Bottom line is, you're controlling the volume of air/fuel mixture getting to the engine; anything that accomplishes that in a stable, repeatable manner is correct. I suspect if you close your throttle plates completely you won't get much over 600RPM on the slow-run valves. Try it and report back. 

British Classic Motors can't spell 'imperative,' how much confidence can you have in their definitive statement ? 


Bob 


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Bob Spidell - San Jose, CA 

----- Original Message -----



Bob 

My understanding was that you adjust the idle with the slow run valve and not the throttle adjustment. In fact i have read in various publications the instruction that the butterfly must be closed at idle. 

Here is an example from a US company called British Classic Motors. 

'On most vehicle applications the idle is controlled by the slow running running valve and this alone must be used to adjust the idling speed. IMPORTANT: It is imperitive that the throttle linkage is allowing the butterflies to close completely. If not, it will not be possible to set the idle speed accurately'. 

Derek