RE: K&B 6550
Garch:
I have a bunch of the K&B ringed 61 engines, my favorite use is to replace a 40-52 engine. More power and no more weight, often the K&B is lighter.
For an example, my Diablo 40 has the same engine you describe, carb and all. I have absolutely no complaint about it. The engine will pull the plane in a vertical take off out of my hand.
The fuel rate is miserly, if you add a Bru-Line fine mesh air filter (BRU-202 from Horizon) you’ll find the fuel rate even better, and the plane will stay clean by eliminating the fuel spray out of the carb.
I am currently assembling a new twin with a pair of K&B 6560 engines, these are the same as yours with the addition of a built in Perry pump and a very large bore carb. The 6560 will keep up with most modern Schneurle ported 60-65 engines.
You can also send yours to Clarence Lee, he’ll add the PDP modification for about $30 and you’ll also have an engine that will keep up with the later designs. It will be louder though.
Your “Block” carb engine is the middle version, the earlier ones had a standard Perry carb, the later ones have what is called the “Ribbed” carb. The ribbed carb was originally supplied with the needle valve at the carb, latest version uses the remote needle.
Choices, choices. Take your pick.
Enjoy it, it’s a great engine.
Bill.