I have Ninja engines for almost a year and I can assure you (as many in this thread could) that power output of the MR21-01 is really great, maybe they don't have the rip of other engines, but it makes it easy to drive it hard (laptimes are there... and easy to do).

The carburation is very stable and sensitive to changes so you will not battle with it. You could do easily 5 minutes with the fuel tank so runtime isn't a big problem except in some tracks.

Comes with the 8.5mm carb venturi and gives good power and runtime. You have the 9mm too if you want 'a little more' but runtime suffers a little.

Is a great engine. Get the engine, pipe and a pair of headers (long and short) and see what suits for your local track.

I don't know in the new units, but.. you need to raise the combustion chamber. Before starting, do a look on the previous messages on this thread just to get what worked for the people and values and compare them with the ones you get from your engine.

The 'gripe' could be the price of the plugs, but... I've been using Sirio ones and work great with them (and of course, are way cheaper). Taper isn't the same, but... after a full year of using Sirio plugs I didn't had sealing problems on the plug.