There would be special tools needed to balance the cranshaft - piston - rod - wrist pin - ring assembly.

But the way it's done is to weigh each end of the rod then you can weigh the rest of the recpricating parts as a lump.

You will make up a "bob weight" that is a total weight that is equal (I Think, if I remember correctly) To all the weight of the big end of the rod + half the weight (this may be a different number? But you get the idea?) of everything else.

This "bob weight" is attached to the crankpin of the crankshaft and the assembly is zero balanced.

The Top Flite magnetic balancer is great for small props/spinners etc but you need a more serious balancer to do flywheels and cranks like the (no longer made) Robart High point balancer or the current production Dubro balancer.

The carb that everyone uses around here on either engine is the Walbro WA167A carb. It has a 7/16" or 11.1125mm venturi. This carb is used on both the 25 and the 30 for model airplane use. This is a real nice carb for model use but any Zama or Walbro carb 10 or 11mm should be fine. The 12mm should only be used on a highly timed engine with a smaller prop. In the USA, the 25's and 30's come with a 8mm carb. The main thing is, you need to be able to adjust both the high and low speed mixture screws.

From looking in the parts book, Homelite lists the same flywheels and crankshafts for both the 25 and the 30. Though to buy a complete short block from the factory, they often look a little different. Even the webbing on the crankcase is larger on my 30. It could be that there are just evolutionary changes in all the engines and everything is interchangeable except the jug - piston - ring?

Enjoy,

Jim