Tuning Your RC Nitro Engine For Optimal Power - A Guide For Beginners
When I first started racing Gas Powered RC cars, I used to struggle to get the engine into tune, while I was able to get the engine to start on a dime and it used to run fine for almost an entire fuel tank, it always seemed to over-heat near the end of the run. After many hours out on the track I can now finally say that I've got it down, tuning for me is now a 5 minute operation before I take my RC car out, and once it's dialed in I only need to adjust one needle a fraction of a turn to get it back to it's optimal settings.
I assume that you understand the basics of a RC Nitro Engine and how it works, if not please see my other articles which you can find on my website, see the resource box for details.
The Idle Screw:
I always start with the idle screw, I adjust it so that the car will idle high when I'm first dialing in the engine. Once I get the engine up to temperature and with a tube that can keep it running without stalling I slowly adjust the idle down to the point where it's about to stall, then I turn it back about 1/4 to 1/2 turn depending on the temperature. If your car stalls often it can be worth while increasing the idle to prevent this, it's only a temporary fix while you sort out the other tuning issue, but it helps keep frustration levels down.
Low Speed Needle.:
One of the great debates is which needle to adjust first, if your carburetor only has one needle adjustment screw then it's not a problem, but if like most glow engines you have two you need to decide which to tune first. I always start with the low speed needle, this is because when you adjust the low speed needle you change the high speed needle. Once the low speed needle is dialed in you shouldn't have to adjust it again. Make sure you keep it slightly on the rich side, when you RC Car idles the combustion chamber should start to fill up with fuel, this helps keep it cool. After a while the engine will stall, by measuring this you can tell if it should be richer or leaner. A good time is about 30 - 60 seconds before it stalls. The RC Car should pull off quickly from a standing start and should not bog down or flame out when you apply full throttle.
High Speed Needle:
Once you have your low speed adjustment needle dialed in it's time to start getting the power out of the RC engine. This is done with the high speed needle, which adjusts the air to fuel mixture of the engine while it as high RPM (about 40% and up). Keep an eye on the trail of smoke as this is your first clue about the tune. You want to have a lot of smoke coming out of the engine at all RPM, if at some point there is little or no smoke then you are running too lean.
Hints, Tips and Tricks:
Turn the needle clockwise to lean out and counter-clockwise to richen the mixture.
A lot of smoke means you tune is rich.
The sound can tell you about your tune.
Reading your glow plug after a run will tell you a lot about your tune.
Make sure to run your engine on the rich side, this will extend it's life.
A lean engine will always put out more power, but it will shorten the life of your engine.
Temperature, air pressure and humidity play if big part in the tune, different days will need different settings.