Fuel Oil Mix Ratio – Two Stroke Mix

Many manufacturers of petrol remote cars have a recommended two stroke mix ratio of 25:1
That is twenty five parts petrol to one part oil.

It is also recommended by many when you first start your gas powered RC car to let it idle and run half a tank of pre-mixed fuel through it before putting any load on the engine.

Some remote control car hobbyists are of the same opinion to let your new gas powered RC car idle for the first half tank of gas.

Others recommend to put in a 20:1 two stroke mix and run the car lightly not more than half throttle for the first two tanks of fuel.

While I know many things about two stroke engines and fuel mixing, I find myself wondering about some of the advice offered out there on the initial start up and break-in period of petrol remote cars. Manufacturers, as we all now, have recommendations that err on the side of caution. Not really good for optimum racing practices.

The engines fitted to these RC vehicles are based on a chainsaw motor. I have never known anyone to to idle a chainsaw for half a tank of fuel before using it and I have worked with forestry workers for years.

There is also the side issue of cooling!

Most chainsaw (and small engine) manufacturers also recommend a synthetic based oil for the two stroke mix (there own brand of course) and the fuel oil mix ratios are 50:1 and higher.

The Advantages of Synthetic Oil over a Mineral based Oil

less spark plug fouling
less smoke or smokeless
use less oil when mixing
longer engine life

The Disadvantages

cost – more expensive
not available at gas stations

The decision on the type of oil to run and the two stroke mix ratio in your two stroke engine is entirely up to you.
Most engines use chrome piston rings, these require some sort of load to help them bed in.

Idling the engine can glaze the bore.

Firstly buy a decent measuring cup and fuel container.

Use this two stroke mix calculator for accurate quantities.

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My view is do not let the engine idle for the first half tank of fuel.
Use a quality synthetic based two stroke oil. Use a fuel oil mix ratio recommended by the oil manufacturer. Start the engine and with all wheels off the ground rev the engine to half throttle and down again. Continue this for a minute or two. The engine should start to feel a little more responsive, as it warms up, when you pull the throttle.

With the engine shut down check it over, make sure everything looks OK and there is nothing out of the ordinary.
Start the engine again and set the idle if it requires it on the low speed mixture screw.

Run a tank of two stroke mix fuel through the engine, with the vehicle on the ground not exceeding half throttle, but also varying the throttle use – idle to half and back down.

On the second tank of premixed fuel, increase the throttle to full throttle but do not hold it there. If the engine won’t rev to full throttle it probably requires adjustment of the high speed mixture screw.
By the end of the second tank of two stroke mix fuel the engine will be run in. You should have set the high and low speed mixtures screws, so it should idle and accelerate to full throttle without hesitation.

Note: Over oiling an air filter with air filter oil can give some symptoms of a sluggish engine or hesitation.

Talk to the team racers at events and ask them questions about the fuel and two stroke mix, many will offer good advice, and much of it will contradict manufacturer recommendations.