I have a 21. I also have a 21 that is still a weed whacker (wife's) and another that is a hedge trimmer. When I converted mine, I found the ports and carb to be terribly small. I put a Homelite 25 carb on it. I wasn't satisfied with the engine because it would only turn a 14-6 at 7,000. I stole some of the conversion parts from it to use on my other conversions. The other two that I never converted continue to function very well as they were originally intended. The engines seem to last forever if taken care of. The trimmer heads are not so durable.

The engine case will trim out to be rather light for a whacker but mine just didn't have enough power though it was easy to start and tune.

Enjoy,

Jim