RE: RB C5 Engine - Starting Advice for New-to-Nitro Guy
You have the same problem I had when I started. You are new to nitro, and don't know what a properly tuned engine should sound like.
Warm your car up on a stand with all the wheels off the ground. Once you have it warmed up, give it full throttle and lean the high speed needle until the engine reaches peak RPMs. Do this a couple times, and if it stops gaining RPMs, or starts to hesitate or stall, you have gone too far. Do this quickly, because these engines don't like to be wide open with no load for long.
It may take a couple tries, but this will give you an idea the pitch. The first time I heard one running right, compared to what I had been running, I thought the guy was trying to blow his motor up. They are pretty high pitched when race tuned. That will get you in the ball park.
You can get your low speed needle set by bringing the car in and pinching and holding the fuel line until the engine dies. It should die within 5 seconds or so, and not increase much in RPMs before it does. If it increases greatly, its too rich, if it dies without increasing at all, its too lean. Once those are close, set your car on a stand, and make the idle as high as possible without making the wheels spin.
Then, just fine tune the engine to make sure you are getting clean acceleration all the way to top RPMs for your longest straightaway, and still seeing smoke between low-mid RPMs.