BIS fuel mixture

[Gadge]

My BIS is fitted with a weber and I had a go at setting the mixture, but I can't make my mind up if I'm making it lean or richening it up? Does anyone know which way the screw goes to make it lean?

[Pete126]

Hi Gadge, you can only adjust the idle mixture because its a fixed jet carb, to adjust the idle mixture gently turn the the mixture screw clockwise (In) until the engine starts to hunt and then gently turn the mixture screw out until the engine runs smoothly, The only way to adjust the main mixture is to replace main jets, emulsion tubes etc preferably on a rolling road

[Gadge]

Nice one, thank you very much 

[gammakeith]

I stripped my Weber the other week as mine was running lean with lots of flatspots.  Its much better now (float level was a mile out) but I had some confusion re the idle mixture adjustment.  On most carbs its a air bleed so winding it out leans it out.  However, the Weber may be other way (ie its a petrol feed).  Certainly, the diagrams in the Haynes Weber manual for related carbs shows it adjusting petrol feed. 

What I found on mine was a lumpy tickover with 1.5 turns out on the idle mixture (usually a good start).  I kept unscrewing and after several turns the tickover suddenly sped up and was nice and stable once I had backed the idle speed down.  Thus, I left it at that which is roughly what it was before.  No idea what the CO is though as my meter doesn't work anymore 

Keith

[Gadge]

I have an automata carburettor manual which covers the 126 BIS weber carb. All it says about the idle mixture is where it's located and if you turn it it will adjust the mix but it doesn't say which way to richen or lean up.

I had I fiddle with it and did what pete said and it runs lovely