This afternoon I was working on the carburettor and setting up the choke after fixing a possible dodgy connection on the choke. Sitting watching the mixture lean out as the choke opened up on my dash displays which can be plugged into the engine bay. Engine idled nicely for a while. Suddenly the AFR shot over to lean. So I took the carb. off and cleaned the idle jet. I put the carb back and took it for a drive.. it did it again.. Then when I got back, I found the hot air flap in the intake was jammed in the cold position. So it was most likely icing not dirt.. I freed the hot flap up, checked it moved with vacuum, and after a while the mixture stabilised again at 14-15:1 AFR. I shot the air plenum above the carb woth a IR thermometer and that showed 28 degrees C on the outside of the box. Or nicely warm... Interesting .. If I didnt have a working hot air flap I would have to drive round with the choke on instead to get a rich enough mixture to counteract icing. Which shows how off tune the mixture has to be if you dont have working preheat .
Pah! 11 is nothing ! Mine starts at 10 and goes up to 20 ! Setting Lean Best Idle gives in the 13 to 15 region. 11 is a sooty bumper, 20 is crackling on the pork..foot hard down should be 12.
