Checking your paramotor spark plug color should be part of your regular maintenance checks. If it isn't, you could be missing some important warning signs from your engine, that could have an effect on its performance, and its lifespan.
The check is really simple to carry out, even if you're completely new to engine maintenance, and you can do it immediately after your next flight.
Spark plug diagram
How to check your paramotor spark plug color
The first thing you'll need to do is remove the spark plug from your engine. Once removed, I recommend putting a new plug in, or you can simply give your current plug a good clean with a soft brass wire brush.
Put the plug back in, and take your paramotor for a flight. It will take a while for the color to appear on your spark plug, so be sure to fly for at least an hour, and make sure the engine is reaching full power with minimal periods of over-idling.
When you land you can remove the spark plug, but let the engine cool down first, as the spark plug will be very hot.
Inspect the plug, and compare it to the images below.
1. Image number 1 shows a sooty spark plug. This is commonly the result of the wrong plug being installed in your machine, which has too high a heat rating.
It's important to check your engine user manual, and be sure to use the correct spark plug as recommended by the manufacturer. An example of image number 1 would be a BR8ES spark plug being used instead of the recommended BR6ES.
Using the NGK numbering system, the higher the number, the colder the heat range of the spark plug.
So if you were using a number 8 plug instead of a number 6, the spark plug wouldn't reach what is known as it's self cleaning temperature. Basically it wouldn't get hot enough to burn away carbon deposits, which always results in a plug that looks similar to this image.
Bare in mind that over idling can also cause this. This is why it's important to check your paramotor spark plug color after the engine has been operating under normal flying conditions.
2. Image number 2 shows a mid brown tan, which is the optimal spark plug color for all paramotor engines. This color indicates that the fuel to air mixture is perfect, and the engine is running at the correct temperature.
There may be a little carbon buildup around the electrodes, but these settings will optimize the lifespan of the engine, and will help to prevent overheating and seizures.
3. Image number 3 shows a white or light grey color, which is indicative of a lean, or weak mixture. The plug will also be extremely dry, this means that there is too much air and too little fuel being fed to the engine.
Running your paramotor engine with these settings will cause the engine to overheat very quickly, and will put it at risk of seizures and a melted piston. In the worst cases the tip of the plug may also start melting away, though I've only seen this once on a friends machine.
There could be a number of causes for a weak mixture, so use the points below to diagnose the cause.
- Wrong settings on carburettor: this is the most likely cause of a weak mixture. If the air screw on the carburettor is turned too far out, excess air may pass into the engine weakening the mixture. Simply turn the air screw clockwise to richen the mixture, until the desired spark plug color is achieved.
- Air leak: An air leak will also cause a weak mixture, so check the cylinder head and base gaskets, read block, and the carburettor clips to make sure no leaks are present.
- No air filter: if the air filter has been removed by a previous owner of your machine, this can also let too much air into the carburettor. Simply replace the filter to solve the problem.
4. Image number 4 shows a wet or oily spark plug that is black in color. This can indicate a very rich mixture, where too much fuel is passing into the engine.
To solve this problem you will need to weaken the mixture, but be very careful while doing so. A rich mixture will not cause the engine to overheat, but a weak mixture will, so when adjusting the air screw use very small increments, and check the spark plug color between each adjustment.
It's better for an engine to run slightly rich than weak, but a rich mixture can still lead to future problems. Carbon deposits will start building up inside the engine and exhaust system, which can eventually cause pre ignition. You'll also get unburnt fuel coming from the silencer, which can then build up on your propeller as it moves past it.
This is why it's worth spending a little time getting your carburettor and mixture settings perfect.
NOTE: an oily plug can also be caused by adding too much oil to your pre mix. Check your user manual to find out the correct amount to use, as recommended by the manufacturer.
Cheap oil can also fail to burn as it should, see THIS POST to find out why a quality oil is highly recommended, and how the cheap and premium brands differ.
Other things to bare in mind
Given the explanations above, it's always a safer approach to use a slightly richer setting. You may loose a small amount of power, but you can rest assured that your engine won’t suffer any damage during those long full throttle climbs after takeoff, or on those lengthy trimmed out cross country flights.
Something else to remember is that air density changes with altitude, so if you fly high you'll experience a richer mixture. With this in mind, I always check my spark plug after flying no higher than 1000 FT, this way I know my engine won't be running too lean when I fly low.
So you can see why checking your paramotor's spark plug color at regular intervals is important for the health of your engine, but it's also important for your own safety.
Keeping our engines in tip top condition is very important to reduce the chance of an engine failure. For more maintenance tips and paramotor service essentials that will keep your engine happy, check out my maintenance post here.