The carb barrel is for their .09 motor. This severly castrates the potential power of this engine. They should have bored the barrel for the common .15 sized motor. They are obviously cutting cost with this an the intake is WAY TOO SMALL! You can bore the exaust as much as you want and it will make little difference because the bottleneck is in the carb. I bored out the barrel as big as the carb intake so that they are flush when wide open. I also used a 1/4 inch circumference and 1 inch long exaust tube in place of the old exaust which is also for the .09 and very restrictive. I bored out the exaust on the can muffler and JB welded the new 1/4 inch tube to it (got it from home depot). I also didn't like the vent tube coming off the side because of the added length of tubing it took to get it to the tank. The longer the tubing the more resistance the pressure to the tank. I learned this the hard way with a JKA mustang when I put the tank too far back in the foam fuse and fuel draw became an issue. Anyway, I tapped a new vent tube coming out the back of the muffler and ran a fuel line directly from muffler in a straight line to the great planes 4 oz tank. (I also plugged the side hole with JB weld). The top end is great but the low end is now very touchy to tune. This is combat so I don't do much idling anyway so I don't mess with it much. You can see picture of it on my SPAD defender at http://www.nearc.rcclubs.com/photo2.html
It't the yellow and red one. It has been dirt napped alot as you can see in the bottom photo. I dirt napped it again today and broke the connecting rod I think. The prop is now freewheeling so I guess thats what happend. Anyway I was just looking at the replacement parts on Global Hobbies and they were pretty cheap. The barrel is only 5$ so if you don't like the bored out verson then buy another (also debur the barrrel with fine grit sandpaper around where the bit ran through so you don't sctratch up the carb housing when you put it in and work it). The connecting rod is only 8$ so I'll have it back in the air in no time. Being a rear exaust, I just bought a kyosho ducted fan for 11$ and will mount it in a duck tape tube and circular wooden motor mount. I have a 95 cent 2 oz fragrence can (like a miniature mousse can) to use to up the performance. I figure if I'm getting 18k with a goofy muffler and 8X3 prop, a mousse can with ducted fan should get me over 20k which would fly the flying wing configuration that Ive been designing in my head for the past several weeks. Anyway, try boring out that carb as far as it will go and see the performance difference. If you don't like it your out 5$. If you do, then you won't be giveing me such a good deal on that engine!