RC Car - Too Hot, No Fuel Economy

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Too Hot, No Fuel Economy

Comments: Hi, I have a Nitro RS4 with a OS CVX in it. I also have the 2 speed transmission along with the stock pipe that came with the car. The engine seems to run fairly hot, around 250 degrees, gets poor gas mileage (I can't even finish a 5 minute race on a tank of gas). The car lacks low end punch too. I put the Kyosho 2 speed on it because when the kit came out HPI didn't have one available yet. Could this all be related to a gearing problem? The car is very fast on the top end. I've tried to run the motor a little richer but it gets even worse mileage and still stays warm. Is there an adjustment for the bottom end on the CVX. Do the after market heads from Alien (the low profile ones) make much of a difference in temps?

Response: First off, if an engine is running excessively lean (too hot) the gas
mileage increases as the air fuel mixture has a higher ratio of air than fuel in it (less fuel in mixture means longer fuel economy). You told me that you can't even make a 5 minute race. You should get at least 7 minutes if not more like 9 or 10.

It could be a gearing problem. The only thing that I can think of is that you are running an excessively high ratio which is causing the engine to spin at a higher RPM range than it should. I guess this could heat up the engine and cause it to use a lot of fuel. This is just a half educated guess though and it doesn't completely check out as you are running a 2 speed tranny.

The CVX has a low end adjustment right in the side of the carb where the throttle arm is. It looks like a circle with a flat head screw slot in it. It adjusts just like the top end valve (main needle). Screw in to lean the mixture and screw out to richen the mixture. The low end valve adjusts from idle to about 1/4 throttle so it greatly affects the acceleration of your vehicle.

In the end it sounds like your piston and sleeve may be worn out. Run the engine and once it gets to operating temperature shut it down and turn the fly wheel over by hand, does it have compression? If not, she is probably dead. You can either replace the piston and sleeve or the entire engine. If the rest of the engines' components are ok (con rod, bearings, crank pin, etc.) than just buy a new piston and sleeve. If the entire engine is tired, replace it and use the old engine for parts.

As for your question regarding after market cylinder heads, I don't think they are a big deal. The stock OS head works great and it looks good too (not to mention the price is right, you don't have to spend any extra on it). I have never had a problem with engine temperatures using the stock head. Besides, some of the guarantees I have heard are completely unreasonable. One ad said 30% cooler temperatures. Sure buddy, let's see, a regular .12 size engine runs at about 230 degrees Fahrenheit, 70% of that (230 x 0.70) equals 161 degrees. Do these companies seriously expect me to believe that my engine temperature will drop by 69 degrees just by switching to their cylinder head? Until I get beaten by an Alien or O'donnel head I'm going to invest my money into upgrades that will actually help me or I will save my money and just practice more.

Let's take off a few tenths per lap,

"PRO"
Pro Racer Secrets