Good work. The lighter flywheel makes for quicker revs. On the other hand, the heavier flywheel gives smoother low rpm running. To mix-and-match flywhwels, use the corresponding release bearing sleeve.

just swapped engines in my WHB310 While doing this I discovered that the A14/15 factory flywheel is about 5mm thicker than the A12 flywheel fitted to the new motor. The thinner A12 flywheel resulted in the release bearing being too far away from the clutch. Problem solved by retaining the A14 thick flywheel. While I had both flywheels off , I weighed them and found the A14 thick flywheel was only 500g heavier than the A12 flywheel.

My question is : on a stock motor, is there any advantage or disadvantage in using the slightly lighter flywheel?