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SOUTHWEST AIRSPORTS

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Priming & starting the engine

By Had Robinson

Introduction

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.

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.

Pilots who become skilled with this technique can start their paramotor with it on their backs.  This is always a much SAFER option than starting it on the ground.

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.  Miniplane-USA supplies propeller covers with a strap for this purpose.  None of this is necessary, however, if the engine is started while on the back.

How to start the engine with the first pull, every time

  1. 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.
  2. 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.
  3. Blow into the primer 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.
  4. Push down on the priming lever on the carburetor for 5-8 seconds.  If there are bubbles or no fuel in the line going into the carburetor, more time will be required to purge the fuel system of air or you did not blow hard enough into the primer tube.  (If there is no priming lever, contact Miniplane USA to order one.)  Hold the lever (and fuel tank pressure) until ALL air/vapor bubbles in the fuel line go into the carburetor and then hold it another (4-5) seconds.  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 primer lever.   

    For the Minari and others with a vertical carburetor, hold the primer 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 primer 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.

    WG8 carburetor priming lever
     
    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.
  5. 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.
  6. 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.
  7. 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.
  8. Open the throttle about one quarter.
  9. 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. 
  10. 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.

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