Many of the LA .40 engines bleed air hole is too small and causes the engine to run too rich at the low end and throttle settings below 1/2 throttle. Completely expose the bleed air hole, start her up, warm her up at full throttle, bring her back to about 1/4 throttle (fast idle) and do pinch test. If she speeds up more than 300 rpm when you pinch and take more than 2 seconds to die then your low end is still too rich and you may have to make the bleed air hole a little larger. Before you do that, try a hotter plug, like an OS 8.

Andy