If your engine has stalling problems, then this troubleshooting guide may help you solve your problems and can help to get you more familiar with the different setting. The content of this guide is general for all 2 stroke nitro engines used in radio controlled cars and trucks. The information is based on an .12 O.S. CV engine.

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by Grant Tokumi
Information Advisor - Robert Harrison

Adjustment Screws
Other Names
Approx Settings
Top End Mixture (TEM) needle valve, high end needle, main needle valve adjusts gas/air mixture at high speeds 2-3 turns out from bottom
Idle Set Screw (ISS) idle screw, throttle stop screw Adjusts engines idling speed carb opening at 1-2 mm
Low End Mixture (LEM) Mixture control screw, low end needle adjusts gas/air mixture at low speeds 1.5 turns out from bottom

Step 1: Test the Glow Plug

The real test of the life of the glow plug is whether it runs better with the glow plug ignitor on rather than with it off. If the engine doesn’t run smoothly with the glow plug off, then its time to change the glow plug. Sometimes this isn't noticeable until the plug is so far gone that the engine won't even run anymore, but sometimes you can still tell.

Step 2: Test for Compression

Low compression results in stalling problems (flame outs), inconsistent idling, and poor performance (poor overall power). An engine with low compression most likely means that dirt or other foreign matter has worked its way into the engine and has scratched up the piston and sleeve. It can also be caused by poor engine maintenance. If you don't do any after run maintenance to your engine, then low compression can result. A section on engine maintenance is given below. To test for compression, just turn the flywheel with your hand. At one point, there should be some turning resistance, making it hard to turn the flywheel any further. The amount of resistance at that point is what you are interested in. The amount of resistance is the amount of compression in the engine. As you keep turning It, it should break free and become easy to turn again. If its easy to turn the flywheel past that point of resistance (one complete revolution is enough), then you have poor compression and may want to consider replacing the piston and sleeve. If you have a compression tester, compression should be around 60psi. When it gets to around 35psi, it's time to rebuild the engine.

Step 3: Adjusting the Engine Settings

Top End Mixture

The top end mixture (TEM) screw controls the top speed of the engine. Turning the TEM clockwise will lean out the engine. Turning it counter-clockwise will richen the engine. The more lean you are, the more top end you get. However, the more lean you are, the hotter the engine gets. Ideally, you want the TEM to be as lean as possible without overheating the engine. When you run the model you must listen to when the motor is coming up onto the pipe. When it does, it should really hit a nice scream and have a clean whine down the straight away. If it doesn't and stays harsh, you are rich and you must lean the TEM. Lean the TEM by turning it clockwise, around 30 degrees at a time. If the engine peaks out then cuts out down the straight, you are way too lean, and the engine is not getting enough fuel so the TEM must be richened. Richen the TEM by turning it counter-clockwise, around 30 degrees at a Time. The correct settings for the TEM should be somewhere around 2-3 turns out from bottom ("bottom" means starting with the screw all the way in).

Low End Mixture

The low end mixture (LEM) screw works exactly the same as the TEM, only it just controls the low end. Does it sound like it runs out of fuel when you accelerate and then it dies (really whiny with a shutter when it stalls), or does it sound more blurbly and plugged up (like it's getting too much fuel and accelerates really slow)? If it sounds more whiny when it accelerates and dies (lean), then try turning the bottom end mixture screw two clicks counter-clockwise (you should be able to feel it click) and give it a test run. If it sounds more plugged up and blurbly when it accelerates and dies (rich), then try turning the screw clockwise two clicks and give it a test run. If you find that any of these adjustments help, continue turning it one click at a time in that direction after each test run until it feels like it's accelerating perfect. Acceleration must be clean, crisp and abrupt. At the end of the straight, the motor should cleanly fall off the pipe into a nice 4-stroking sounding idle when you let go of the throttle. If it doesn't the LEM may need to be richened. The correct settings for the LEM should be somewhere around 1.5 turns out from bottom.

Another way to tell if your LEM is too rich is by starting your engine and getting it warmed up. Then bring it in and pinch the fuel line with your fingers (be careful of the flywheel!) and count how long it takes to stall out. If it takes more than 4 or 5 seconds to die, it's too rich and you should take a screw driver and turn the LEM clockwise one click to lean it out a bit.

During break-in the bottom end adjustment has to be rich to compensate for the rich TEM. This means that after break-in you almost always need to lean out the LEM a bit after leaning out the TEM. After playing with the LEM for a while, you get used to how much punch it should have for the temperature you run it at and you can always set it for that amount after break in or whatever else you might have done. Nevertheless, you should be able to just let that motor sit and idle forever without stalling.

If your looking for more power, leaning out the TEM will only give you top speed. Only leaning out the LEM will help with torque and punch off the line. Also, any leaning of the TEM also makes the LEM adjustment turn a little richer, so watch for this. Also, watch the temperature of the engine! Leaning the LEM really makes it heat up faster, so make sure you don't go too far! As you LEM, the idle tends to go up, and you must compensate for this by turning down the idle using the idle set screw on the front of the carb.

Idle Set Screw

The idle set screw (ISS) controls the idling speed of the engine. Simply turn the ISS clockwise a little to make the idle speed go up, or turn it counter clockwise to make the idle speed go down. You can adjust the ISS any time you want and it won't change anything other than how fast the engine idles at. Try to adjust the ISS while there is no servo pressure on the screw. This means give the engine just enough throttle from idle to allow the pressure on the screw to be released. This will prevent a stripped out ISS. When the ISS is set correctly, the carb should very slightly open with the opening at around 1-2 mm wide.

Step 4: Check the Engine's Temperature

Have you ever checked the temperature of the motor when it's been running for a while? Heating a motor up really hot seriously shortens your motor's life span and shouldn't be done at anytime.

The Spit Test - You must have heard of this method to check the general temperature of the engine. After running for a minute or so, you just spit on your finger (plenty of spit), wipe it on the motor heatsink head, and if it boils away really quickly, it's too hot and therefore too lean, so you should richen the TEM by turning it counter clockwise a few clicks (I emphasize the few, not just one). This should cool it down enough to make the engine last a bit longer than it would at that lean setting. Normal running temp is around 210 or 220.
However, don't think that running a motor very rich all the time so that it is barely warm to the touch is healthy. Running too rich causes the walls of the sleeve to stay very wet and cool, while the combustion chamber temp is much higher. This can cause the sleeve to not expand according to the piston expansion creating more wear then if you were running normally. A properly set engine can give blistering performance, and if the fuel is clean and fresh, and if the air filter is doing its job, the engine will last very long.

"End of the Day" Engine Maintenance

Keep the Dirt Out!

Your #1 concern: You never want ANY small dirt particles to get inside your engine. Lets say that again. You never want ANY small dirt particles to get inside your engine. There are three major places where dirt can get inside the engine:

Fuel Choice

Blue Thunder or O'Donnell seems to be the recommended fuel to use. Certain fuels may have a tendency to heat motors up unnecessarily. Blue Thunder or O'Donnell don't seem to do this. On the otherhand, if your fuel works fine and you are not familiar with adjusting the settings on the engine, then by all means, don't change your fuel. Settings need to be changed when you switch fuels and you may end up with more headaches if you are unfamiliar with tuning an engine to the different fuel. As the saying goes, "If it ain't broken, don't fix it".

Head Shims

As a general trend, the removal of head shims increases compression, increasing output, highering operation temperature, and resulting in the use of lower nitro. Less compression allows higher nitro use, less strain on the motor, less bottom end, sometimes higher top end.

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