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High Performance for less!

2-Cycle Engine Operating Tips

The following tips are gathered from personal experience, Web Sites, Forums and modelers in general. This information is intended as a guide and should be used as such.

Fuel Systems

BCMA-SPORT26/40 Carburetor and manifold installation/removal:

In some cases BCMA Engines will be shipped with the carburetor and intake removed. Also there may be a point in time where the carburetor needs to be removed to be replaced, serviced, or general maintenance. It is very important that the carburetor and intake be properly aligned for the engine to function properly.

When installing the carburetor, it is imperative to align the pulse line of the carburetor to the corresponding pulse line on the intake manifold. Carburetor throttle arm should be pointing straight down towards the crankcase of the engine.

Make sure your gasket is installed correctly so it is not blocking the pulse line or any carburetor bolt holes. Looking at the manifold it can only attach one way. make sure that the side with the round carburetor hole is facing you. The rectangular hole on the opposite side must mate up to the intake port of the engine.

Tank Placement:

Most modern gas motors have carburetors that have pumps and regulators built in. This means that you can mount the fuel tank almost any where in the

plane. It is recommended that you mount the tank as close as possible to the center of gravity. You don't need or want to try and use muffler pressure

instead a vent line will need to be run out the bottom of the plane so the tank does not pressurize.

Carb Setting

Initial carb needle settings:

When you get a new carb and are not sure where the needle settings are it is best to start at a good ball park setting.

Turn both needles in all the way and back them out about 1 3/4 turns out. This will be a very rich setting but your engine will start at this point. Once it is running than you can lean them out.

Adjusting the low speed Needle:

Note: Make sure your engine is warmed up before you adjust the carburetor.

Idle down for a few seconds then punch the throttle to wide open, if the engine loads down in the middle of the transition, lean the Low Speed needle 1/8 turn at a time until it transition improves.

That will be as rich as it needs to be on the low end. Once you have that sorted out, adjust the idle trim.

You might have to richen the low end to get a good transition or to insure good down line breaking, but remember to keep the bottom end as lean as is practical. This will help insure a good midrange response.

Now retouch up the top end and check the idle once more. On a gas carb, the low end will affect the high end but the high will not affect the low.

Adjusting the high speed Needle:

Run the engine wide open and adjust the Hi-speed needle slightly rich of full RPM since the engine will further lean out in air.

Starting your Engine

Manual Priming and choking:

Most of my carbs do not have a choke plate basically because they are not at all needed and its easier to manually choke the engine anyway.

Do not squirt fuel into the carb, this will not accomplish anything if the carb is not primed.

To prime your engine, turn your ignition off and put your thumb over the carb opening (This is easiest with a Velocity Stack)

Set your throttle set to wide open

Now rock the prop back and forth (It is not necessary to rotate the prop).

Do this until your thumb is wet with gasoline. Note: If your engine is mounted inverted too much priming will flood it so don't over do it.

Now turn the ignition on and set the engine just a crack above idle and with an electric starter crank over the engine and it should start immediately.

If it won't fire, than you may have flooded it. Remove spark plug and dry it off and re-install it.

If your engine is mounted inverted, after each use it is a good practice to remove your spark plug and clean it with carb cleaner after flying your plane.

During hanger time all the unused gas and oil will pool up in the sparkplug and when the gas evaporates it will leave behind oil and gum and if you don't

remove it it will prematurely foul your plug. Its also a good idea to keep new spare plugs on hand as well as a can of carb cleaner.

Note: Be careful not to spray the engine with carb cleaner, it will instantly remove engine paint.

Carburetor Troubleshooting

Engine Troubleshooting

If you have an engine performance problem and suspect the carburetor the first thing that must me done is to confirm that you actually have a carburetor problem. Below is a trouble-shooting guide that can help you diagnose engine problems that can often be mistaken for the carburetor. I will assume you have confirmed the following items and inspected all the possible faults listed below:

Good ignition system and spark plug
Crankcase pulse passage or line is clear
Carburetor and manifold bolts are tight to ensure an airtight seal to the crankcase
Low speed and high-speed needle settings are adjusted properly

Fuel/Oil mixture

Most 2-cycle oils on the market will work with R/C Gas motors. Saying that, high-quality synthetic oil will burn cleaner and help the motor last longer. I do not recommend breaking in your engine using synthetic oil since it will prolong break-in period. For break-in and just normal operation I recommend using Pennzoil for Air Cooled 2-cycle Engine oil for your engine. If you wish to use a good synthetic oil I recommend using Klotz, Mobil1, and AMSoil. I do not recommend using oil mixtures exceeding 50:1 and doing so will void your engine warranty.

A note on mixture:

A Glow motor relies heavily on its fuel for cooling and timing. The Gas motor on the other hand really doesn't rely as much on fuel for cooling and has a regulated carb. This means that you set the high end for peak and go rich only slightly, not enough to realize an RPM change. This is important because if you set it too rich, you will have a horrible midrange response.

Electronic Ignition

Installation of Ignition:

If your engine is equipped with a CH-Ignition attach the supplied ground wire to one of the crankcase bolts of the engine as pictured below:

Ignition module can be mounted either on the firewall with Velcro or secured with zip ties. Make sure it will have any contact with fuel and make sure your wires are neatly tied down to avoid them getting melted by the heat from the muffler or cylinder head.

Ignition Batteries:

Why I recommend using a 4.8 Volt battery vs. 6.0 Volt battery with my ignition for the following reasons.
A 6.0 volt battery will pull more current on the ignition than a 4.8 volt battery giving you less operation time.
Using 6.0 volt battery will increase the intensity of the spark slightly but not enough to benefit you.
A 6.0 volt batter will require a voltage regulator and larger capacity cells creating more on-board weight and complexity.
With lower current draw on a 4.8 volt pack you can use smaller capacity cells for less on-board weight.

Ignition Timing:

On Homelite chainsaw engines I set the timing between 28 and 30 degrees BTDC (Before Top Dead Center)
On the BCMA-SPORT26 and BCMA-SPORT40 Engines are factory set at 30 degrees BTDC (Before Top Dead Center)
Setting ignition timing outside of these points will degrade engine performance!

A note on Radio Interference:

If you run electronic ignition Radio Interference is always a possibility. If you encounter this problem here are some ways to help reduce or eliminate this problem. Usually this problem is easy to fix and is a matter of trial error since everybody's plane is somewhat unique and some radio systems are more sensitive than others.

General Rules:

Never use metal throttle linkages, metal rods will act as an antenna and direct noise to the servo and from the servo to the receiver.
Keep ignition unit as close to the engine as possible and any radio equipment as far away as possible including throttle servo.
Use a Resistor Spark plug such as a Champion RCJ6Y (Homelite) or NGK BPMR6F (BCMA-SPORT).
Keep ignition battery separate from the radio receiver battery.
Make sure your spark plug boot is seated all the way down on the plug.

If you are still experiencing problems, here are some more extreme measures:

Wrap your ignition module with Aluminum Foil.
If your ignition module is mounted on your firewall, apply HVAC foil ducting tape to the firewall.
If your ignition module is inside a compartment, line the compartment with either Aluminum foil or HVAC foil ducting tape.
secure a hose clamp around the spark plug boot to ensure a solid ground connection.
Upgrade to a PCM type radio system.

Prop Hub

Prop Hub Components:

The prop hub on the BCMA-SPORT26/40 is a two piece design. In case you are wondering why there are (4) screws on the prop hub face they are used to fasten the face of the hub onto the main body of the prop hub. The main Hub is fastened to the crank shaft with a single 8mm bolt. The prop hub is also keyed to the crankshaft. It is highly recommended to check the tightness of the screws that hold the face plate on every time you change props. Failure to do so can cause the face plate to come loose and cause severe vibration. If you remove these screws use locktite when re-securing them.

Multi-Bolt (No Slip) Prop installation:

There are (2) long screws that are included in your hardware package that came with your engine. These will be used if you choose to use this method of securing a propeller to your engine. Note! This is purely optional and not required. Also you will need to secure the main prop bolt. Do not omit this! The (2) bolts are only to keep the prop from slipping or loosening up.

You can also replace the (4) screws that holt the prop hub face on with a total of (6) long screws to populate all the holes on the prop hub. Again, do not omit the main prop bolt!