Priming & starting the engine
By Had Robinson
Here is how to prime the engine so it will start the first pull – every time. This technique will not flood the engine. Pilots must be able to easily position the inlet side of the
carburetor lower than outlet side. Note: With engines where the carburetor is mounted vertically, a slightly different technique must be used – see below.
If you do not know the parts of a carburetor, study this diagram of the WG-8 carburetor or the WB-37 carburetor.
Note that the diagrams are of generic carburetors and that the actual shape of some parts of your carburetor may be slightly different, such as the metering diaphragm cover and the fuel pump
The priming lever (or spring) is not present in the diagrams. Depending on the model carburetor, it may be missing entirely or look like either of the following photos. If it is
missing, use a broken toothpick to push down on the metering diaphragm beneath the cover.
A flooded engine
will take a lot of pulling on the starter to clear things up. It may
be so flooded that the engine will have to have the carburetor and reed
valve removed in order to drain out the accumulated fuel and oil. I
have actually seen this happen. Frustrated pilots routinely damage
their starters trying to start flooded engines.
Additionally, using this
technique will also tell pilots that the fuel system
is in good condition. (Go
here to get more info on how to easily test
the fuel system.)
No engine will start easily unless the ignition and/or
carburetor adjustments are in order so be sure these are OK first. The low speed idle adjustment is precise
and needs to be accurate for the engine to start or run smoothly midrange.
A broken core in the secondary wire, a fouled, old, or loose spark plug, or bad/old fuel will
always make the engine hard to start.
Note: If pilots must start the engine on
the ground, ALWAYS put the throttle hand on the engine frame in such a way that
the sudden start of the motor does not cause the throttle
to increase accidently!
BE CERTAIN THAT THE THROTTLE IS IN YOUR HAND
WITH YOUR THUMB READY ON THE KILL BUTTON!
A run-away paramotor is
both terrifying and dangerous and pilots must always be ready to shut it down. (Don't ask me how I know this....)
Kill switches can fail. This is why newer pilots should use their
glider strap or a line to tie the propeller to the cage (clutched engines only) until they get
thoroughly familiar with their engine.
propeller covers with a strap for this purpose. None of this is necessary,
however, if the engine is started while on the back.
Jeff Goin, President of the USPPA has these warnings about starting a
paramotor. Don't be an idiot! (Yours truly is working on it)....
How to start the engine with the first
pull, every time
- Time limit –This technique is only good for about (5) minutes because the fuel will evaporate and the prime will be lost. Modify the times
given in the steps below for your particular engine, as needed.
- Tilt the paramotor –Facing the rear of the engine, tilt the paramotor to the right about 20 degrees so that the intake of the carburetor is just
pointing down from the engine side. (This step cannot be done on engines with vertical carburetors.) If this is not done, the engine can flood. The principle is that extra fuel will run
harmlessly out of the carburetor instead of into the engine, flooding it. However, do not tilt it excessively because you want some fuel to be present in and about the carburetor throat.
- Blow into the priming tube on the fuel tank
as hard as you can. Use the tip of the tongue to hold the pressure. There has to be enough air pressure to raise the fuel in the tank about 18" (the distance from a near empty
fuel tank up to the carburetor on the engine). If you have a primer bulb, squeeze it repeatedly until resistance is felt, then squeeze again and hold it.
- Push down on the priming lever (a.k.a. the "primer spring") on the carburetor for 5-8 seconds. If there are bubbles or no fuel in the line going into the
more time will be required to purge the fuel system of air or you did not blow hard enough into the priming tube. (If there is no priming lever, order one from
Miniplane USA or use a toothpick.) Hold the lever (and fuel tank pressure) until ALL the larger air/vapor bubbles in the fuel line go
into the carburetor and then hold it another (4-5) seconds. If you are using cheap fuel or the weather is hot, you will not be able to get rid of the vapor bubbles (not air bubbles)
in the fuel system. The bubbles can be so many that the engine may become starved of fuel and will not start. Pouring cold water over the carburetor and fuel tank will fix this
problem temporarily enough to start the engine and launch. If the priming lever is held down too long, causing fuel to go everywhere, it does not matter because the fuel will harmlessly
accumulate in the airbox and/or run out of it. The engine will not flood. Most pilots do not prime the engine long enough.
If there is a foam-type filter in the air box, the
system will be more sensitive to flooding, even with this technique. If there is enough fuel that has flooded into the filter, the fuel vapor can saturate the space inside the filter so
that the engine acts like it is flooded. In such a case, you may have to be more careful experimenting with the number of seconds needed to hold down the priming lever.
For the Minari and others with a vertical carburetor, hold the priming lever down
for about 5 seconds. This assumes that the fuel system is purged of air. If does have air or bubbles, hold the lever down to complete the purge and then another 3-5 seconds. It is
easy to flood these types of engines. You will have to get familiar with how your engine works. How many seconds you need to hold the priming lever down can vary but you will learn how your
carburetor and engine function so as get just the right amount of fuel in the engine to prime it.
Most engines: If
the air box is removed, you can watch fuel dribble out
of the carburetor (except the Minari where it dribbles into the engine and floods it). If it does not, you know you have a fuel system problem and the engine will never start until it is fixed. Note: the fuel filter will always have some air/fuel vapor in it. It rarely means that there is a fuel system leak.
THE ENGINE MUST BE STARTED
WITHIN A FEW MINUTES OR THE PREVIOUS
STEPS MUST BE REPEATED. THIS IS BECAUSE THE FUEL WILL EVAPORATE
FROM THE CARBURETOR THROAT AND AIRBOX AND THE PRIME WILL BE LOST.
- No choke – do not
use the choke. It is unnecessary if the engine is primed
correctly. When this technique for starting the engine is mastered,
the choke is not used except to stop the engine in an emergency
(failed kill switch), to start it mid-air after the engine has been stopped for 5-10 minutes or more, or if you are unable to prime the engine for some reason.
- Put the paramotor on
your back. This is optional. It is unnecessary to start it while it is on the ground and always safer to start it on your back. However, if you did not prime it
correctly, you will have to remove the engine from your back and start over which can be a nuisance.
- Slowly turn the
engine over 3-4 times with the starter. It takes little
effort if done slowly enough. This will charge the crankcase and cylinder
with the fuel/air mixture.
- Open the throttle
about one quarter.
- Pull gently and slowly (non-flash starters only) on the starter rope until the
compression stroke of the engine is felt. Hold the starter in this position for a few seconds. You want the piston to be about an inch before the top of the cylinder with no
pressure in the cylinder. Holding it a moment allows the pressure to bleed off. Be certain to let the starter rope retract fully before continuing with the next step.
- Pull smoothly and steadily on the starter to turn the engine over.
NEVER YANK ON THE STARTER. It should immediately fire and start running. This works for both flash-type starters and standard starters. Do not pull so far that the starter cord is pulled
to the end. If
it is pulled to the end
regularly, full strength used, the pull handle yanked, or pulled
repeatedly, the starter can be damaged. Remember that anything amiss with your carburetor or ignition is not cured by repeated attempts to start the engine.
The engine can be hot or cold. If it does not start the first pull, you probably did not prime it long enough. It may take a few times for you to master the idiosyncrasies of
your carburetor/engine combination.
A flooded engine may have to have the spark plug and air box removed,
the throttle tied open, and an hour to sit for things
to dry out. This can happen if step #1 above is not done correctly.
If a pilot is careful, the starter
will also last much longer – even the life of the engine. I have never had to replace a starter on my Top 80, only
the cord after a few hundred hours of use.