Started getting off-idle stumbling, hesitation, on left XS1B BS38 carb. Pulled carbs, left carb failed the diaphragm drop test. Plugged starter circuit, still fails. Found the JBM diaphragm was no longer a snug fit on the slide. Easily rotated, easily removed. It appears that the diaphragm has swelled slightly, providing a loose, leaky fit. Even the outer ring is larger, almost too big to fit in the carb body groove. I installed these about 1.5 years ago. Using only hot soapy water, the diaphragms were quite a snug fit on the slide necks. And, after drying, were rock solid locked in place.