I have one in my 1/8 buggy and it HAULS. I bought it about 4-5 years ago so it has been out for awhile, succeeded by the C5 and C6. The C4 lacks some low end grunt but that's comparing it to it's own top end but comparing to other motors it's still crazy fast. You will find that the Mugen 1.1 mm clutch springs work well smoothing the throttle response. I have been running O'Donnel 20% and I have never used after-run and it starts up every time even sitting for 6-8 months..no build-up inside the case. There are other fuels that are good like the Cool Power but I would use either, the O'Donnel is probably the most consistent fuel I have used and the C4 holds it's tune very well.
How used is this motor or is it still new? You can get a replacement piston/sleeve from the C5 which is a match so parts are still avail. If you don't have LHS support for RB engined then ACE
is a great place for parts and glowplugs. If you have never used one of these beasts then you are in for a treat, they are gas hogs but for bashing who cares
Once you get it tuned they are silly fast and they like to run RB pipes but any will work. The new 2045 pipe would compliment this motor perfectly. Any questions lemme know.