Troubleshooting your paramotor

by Had Robinson
updated September 23, 2019

Introduction

The tests below cover the (3) major areas:  Fuel system, Ignition, and Mechanical tests.  There is no substitute (except spending money) for learning how your paramotor functions.  THERE ARE NO SHORTCUTS!  YES, YOU MIGHT AVOID THE HARD WORK OF LEARNING HOW THESE ENGINES WORK.  You might also get lucky and win a lottery or be struck by lightning....

Here are the most common issues I (and others) have found that cause problems in paramotors.  When looking through this information pilots should also reference the respective engine specifications page for additional and critical data for their motor.  Even though these pages are specific for the listed motors, the information is largely the same for all (2) stroke paramotors.

It is always a good idea to do all of the suggested tests as, often enough, there can be more than one issue that is causing problems.  Note: Pilots must exercise greater care when using gasoline containing ethanol.  Please follow these recommendations.

The simple tests below only detect major issues with the engine.  The majority of problems with paramotors are fuel related.  If you do not understand how diaphragm carburetors work, the tune-up page on this site is a good place to start.  The carburetors used on paramotors were designed for chainsaws with fuel tanks at the same level as the carburetor so it should be obvious that fuel starvation is, by far, the most common problem we face.

If you are not mechanically inclined or gifted, find a chainsaw, kart racing, or dirt-bike shop to do the work for you.  It will be expensive.  They are the most familiar with diaphragm carburetors which are used in most paramotors.  Chainsaw shops are the best because quality chainsaws use the Walbro carburetors.  Few others know what they are doing, especially the lawn mower shops which, often enough, will wreck your engine.  Most motorcycle shops know little or nothing about diaphragm carburetors because modern motorcycles have 4 stroke engines and are fuel injected.  Nonetheless, there are old guys who know what a Walbro is and understand its common problems.

The WG series is generally used on engines that are 130 cc's or smaller, like the Top 80 or Thor 100 or 130.  The WB series is used on many larger engines.  Engines larger than 200cc generally use float-type carburetors, like the Bing or knock-offs.

ZAMA has this handy troubleshooting chart which applies to all diaphragm carburetors.  It helpful for understanding how these simple, effective carbs work.

You must be able to identify the parts of your engine to do these tests.  Refer to your engine manual or the pages on this website for help.  If you have never changed the spark plug on a lawnmower or have no idea what the little screws do on a carburetor you should, perhaps, have someone else do the work for you.

PARAMOTOR SERVICE – On a limited basis we can service paramotors and the various subassemblies but it must be done at our shop.  Once we ship things back to you, we cannot provide further assistance e.g. how to correctly install a spark plug, reinstall an exhaust system, reconnect the throttle, adjust the carburetor, align the redrive, etc.  If this kind of additional help is needed please contact your dealer, a competent local mechanic, or you may ship us the complete paramotor including the propeller and we can do it.

A. The basic stuff

Are you certain the following have been done accurately before wasting your time and money?

B. Fuel issues

The expected problems

If you just want to begin the tests without an overview, go to Quick fuel system test below.

Do NOT waste your time with these tests if the carburetor has not been rebuilt within the last year.

Using the tests below, you can analyze and then fix these annoying fuel issues in most circumstances.

There are numerous areas of the fuel systems in most paramotors that can cause fuel starvation either alone or in combination.  Remember that if your operating conditions are not perfect (70F/25C) at sea level, you can expect performance issues if there is/are any/even marginal problems.  These can be:

The Walbro carburetors were designed to be used on chainsaws with a fuel tank at the same level as the carburetor.  As a result of this design, the fuel pumps inside the carburetors have difficulty pumping the fuel from a tank 50cm (20") below.  Here is a video of fuel starvation occurring in a Top 80.  In this video, it occurred within a few seconds.  However, sometimes it can take up to +15 minutes.  This is because the fuel system components can supply almost enough fuel but not enough.  The closer the requirements and supply are (in a negative way), the longer it takes for the engine to experience fuel starvation.  If the CHT is monitored during this event, it will be evident that the engine is leaning out by the slow increase in the cylinder head temperature.

It is assumed that the correct FRESH fuel and oil at the proper ratio are being used.  Check this page first if there is any doubt.

If you have a Bing carburetor or a float-type carburetor like it, you will need to purchase the respective service manual.  Here is the Bing service manual.  The Bing is much more complicated to tune than the Walbro.  The Bing service manual is more a tedious discussion with page after page of irrelevant detail than a useful set of instructions for pilots on how to tune it.  It needs to be completely rewritten by an actual service technician.

An improperly adjusted metering lever (ML) can cause a sudden or delayed (3-8 seconds) stoppage of the engine when the throttle is fully opened.  An incorrectly adjusted ML may only cause problems in cold weather but not in summer/warmer weather or it may limit the top speed of the motor but only sometimes, depending on the fuel type.  The tests below will pass but the ML adjustment can still be incorrect and the engine will experience problems.  See Fading/stopping near/at full load below for more information on this issue after you perform these tests.

Fuel starvation is the #1 problem that I see in the motors coming in here.  It leans out the engine and can destroy it due to overheating.  Really severe fuel starvation happens so quickly that the engine will simply stop running before it overheats.  Backing off the throttle quickly will usually keep the engine running.  Symptoms of fuel starvation can be rough idle, no idle, and/or decreased power output (fading), including near stoppage, at full throttle.  Damage form a lean condition can include stuck piston rings, scuffed cylinder walls, low compression, and actual holes in the top of the piston.

Some paramotors actually come with NO INLINE FUEL FILTER.  It is hard to believe....  If this is your situation, install one using the information on this page.  Auto parts stores DO NOT have the right type or quality of inline fuel filters.  However, some may have the WIX line of inline fuel filters which are of high quality.

Easy check to determine if a carburetor rebuild may be necessary

Though not always 100% accurate, the suppleness and condition of the diaphragms in the carburetor can be easily determined.  WHEN IN DOUBT, REBUILD THE CARBURETOR!

  1. If possible, start and run the paramotor for 5 minutes or more.  If it will not start, prime the engine making sure there are no bubbles in the fuel line where it enters the carburetor back to the inline filter.  Bubbles can be removed by tilting the engine so that they move into the carburetor.
  2. Let the engine sit for an hour.
  3. Carefully observe the fuel line where it enters the carburetor.
  4. If there is a gap of air of any size in the fuel line at the inlet, it means the check valves in the fuel pump circuit are leaking and a rebuild is necessary.
  5. Diaphragms in good condition will hold the fuel in the carburetor for a day or more, even a week.

Sometimes, the diaphragm material can be so deteriorated that you can watch the fuel actually drain back into the tank after the engine is stopped.

 Parts of the fuel pump diaphragm are used to create the check valves inside the fuel pump circuit.  If these valves leak at all, the fuel pump capacity and pressure will be less, especially at full throttle causing a lean condition/fuel starvation.  Typically, the diaphragm material stiffens and decays after exposure to gasoline, especially if it contains ethanol.  This happens even if the Teflon diaphragm included with the kits is used.  However, the Teflon diaphragms will last longer and should be used with ethanol fuels. 

Quick fuel system test

This test will help you to see if fuel is able to pass through all of the tubes, filters, and valves of the fuel system including all parts of the carburetor.

  1. Remove the airbox/filter, if there is one.
  2. Tip the engine so that the throat of the carburetor is lower than where it attaches to the engine.  This must be done so that fuel will run OUT of the carburetor and not INTO the engine.  Some engines, like the Minari, cannot be easily tipped to prevent possible flooding.  In this case, hold the throttle wide open with a piece of tape or string wrapped around the throttle handle.  This will help fuel that runs into the engine evaporate quickly.
  3. Pressurize the fuel tank with the priming tube and hold the pressure with the tip of your tongue OR the primer bulb.  I use a piece of windshield washer hose to connect to the priming tube so I can better see what is going on.  If you have a primer bulb, maintain pressure on the bulb to do this test.
  4. Press down and hold the priming lever on the carburetor.  (With the Minari, ONLY hold the priming lever just long enough to see if fuel begins to dribble out of the main jet and holes in the throat of the carburetor and down into the engine.)
  5. Fuel should dribble in a steady stream out of the carburetor.  (For the Minari, leave the throttle wide open for another 10 or 20 minutes while you are doing other tasks so that the excess fuel can evaporate.  It is very EASY to flood engines that have the carburetor on top.)
If the fuel does not dribble out, remove the fuel line going into the carburetor and use the priming tube (or primer bulb) to pressurize the fuel system again.  If fuel comes spurting out of the fuel line, you know something in the carburetor is stopping the flow of fuel, probably a clogged fuel inlet screen.  A rebuild of the carburetor is necessary.  If little or no fuel comes out of the fuel line, you probably have a clogged inline and/or tank filter or a crushed fuel line.  Ethanol fuels often create goo that can clog the pickup tube filter inside the fuel tank.  Take it out of the tank and examine it carefully.  I recommend that pilots drill holes in the filter to ensure a full flow.  It does nothing as a filter. 

Perform this next test on the fuel pump if step #5 above passed.

To test the fuel pump:

  1. Remove the spark plug.  Reconnect the spark plug to the secondary (the plug) wire and lay the plug down in the area near the spark plug hole so that the metal shell of the spark plug touches a metal part of the engine.  (This MUST be done to avoid damaging the ignition coil due to overvoltage.

  2. Remove the airbox/filter, if it is not already removed.

  3. Tilt the engine to the carburetor side about 40 degrees.  (With the Minari, see step #2 above in the "quick fuel system test".

  4. Push down on the priming lever.

  5. Crank the engine.  This is not easy to do while tilting the engine.  Fuel should dribble out of the carburetor throat.

  6. For the Top 80 and all engines that use the WG-8 carburetor with an internal pulse port (through the reed valve body)  The step above (#5) can pass with a newly rebuilt carburetor OR with a brand new engine.  But when the engine is run off idle (1/4 or more throttle), it suddenly dies.  It may act as if the ignition is shorting out because the engine stops very suddenly.  This problem is unique to the Top 80 because of how the fuel pump is powered.  The reed valve body may be loose and the passageway between the crankcase and the fuel pump is leaking air around the gasket or the passageway is restricted or clogged.  Another problem is that the gasket between the carburetor and the reed valve body can shift enough that it blocks the port that transmits the pulses from the crankcase to the fuel pump.

    A telltale sign on new or used engines is the presence of unburned oil around the carburetor-reed valve gasket.  The suction of the carburetor and a partially working fuel pump will allow the engine to start and idle.  If more fuel is required (and, especially, the engine is warming up), the pump will not deliver enough fuel to the engine – and die.  A cold engine has a tighter fit.  When it warms up, things expand and this increases the problem of a loose reed valve body.  In addition, the pump will not work if the passageways to the crankcase are not sealed and clear of obstructions.  If the carburetor gasket is put on backwards or upside down, the fuel pump will not work even though the engine may run, though poorly.  This problem creates a lean condition and it is easy to burn up the engine.  In addition to this, Miniplane has been installing carburetor-reed valve body gaskets that have a gasket with a reduced diameter pulse port hole and which is also offset (see photo below).

  7. For other engines  If step #5 above fails, remove the fuel pump pulse hose (at the carburetor end) that goes from the crankcase to the carburetor.  Crank the engine again.  You should hear and feel a "whoosh-whoosh" of air going in and out of the hose as the engine is cranked.  There will be a few pounds of pressure in the hose as the engine turns over.  If this test fails, something is blocking the flow of the air pulses from the crankcase that work the fuel pump.  It could be something in the hose or the fitting that screws into the crankcase that is clogged.

  8. For all engines  If the test in step #5 or #7 above fails, then something is wrong with the carburetor fuel pump.  It could be debris in the pump valves, a bad diaphragm, or a clogged inlet filter screen.  In any case, the carburetor will have to removed, disassembled, and thoroughly inspected.  If there are any doubts per the conditions of the metering lever and fuel pump diaphragms, rebuild the carburetor.  Pilots need to look carefully at the carburetor and see if they can spot the problem.  If this step is baffling, send the carburetor to us and we will take care of it.

  9. If there is any doubt about the performance of the fuel pump, perform a thorough test of the fuel system.

If all of the above tests pass, the fuel system is most likely OK and you can go to section "B" below and do the simple ignition test.  However, if you have experienced fading and/or stall at/near full throttle, you should check the metering lever height in the carburetor and also be certain that there is nothing obstructing fuel flow.

If there is a lot of dirt in the fuel system, the low speed needle valve may be clogged (a rare event).  Remove the needle and blow out the disassembled carburetor with compressed air.  A clogged low speed needle valve would only affect the engine at low speed.  If you are still having problems with the fuel system, there are some additional notes in this section.

Below is a photo of an OEM carburetor/reed valve body gasket from a brand new Top 80.  The hole (red arrow) that connects the crankcase to the fuel pump is offset and smaller than the holes in the passageways between the carburetor and the crankcase.  It is about 70% restricted and the crankcase pulses that power the fuel pump are too weak to the do the job.  The machine at the Miniplane factory that stamped out the gasket did not have the correct dimensions.  In addition, the reed valve body screws on the engine were loose.  (See the Top 80 specifications page for the correct torque that should be applied to these screws.)  The metering lever value was also incorrect.  This brand new Top 80 would not run under high load – and wound up here in our shop.  It also had other problems that compounded the faulty gasket.

Defective Miniplane carburetor-reed valve body gasket

Modified OEM gasket.  A leather hole punch was used to make the hole in the gasket the correct size.  To prevent damage to the gasket, use a piece of masking tape to cover both sides of the existing hole and THEN punch the new hole.  The punch itself tends to expand the outside of the new hole and will split the gasket if masking tape is not used.

modified Miniplane carburetor-reed valve body gasket

Thorough fuel system test

If fuel does not dribble in a stream out of the carburetor in the tests above, perform a thorough test of the fuel system.  If it has been a year or more since the last rebuild, it is time to rebuild the carburetor regardless if there are problems with performance.

The insides of the carburetor age in the presence of fuel whether the engine is run or not.  Ethanol fuels attract moisture which, as the outboard motor guys know, will corrode the metal parts made of anything but stainless steel.

Here is an OEM fuel filter from Miniplane that was damaged by ethanol gasoline that had water dissolved in it.  This is why ethanol fuels should not be used in 2 stroke engines unless absolutely necessary.  Ethanol fuels should always be tested for the presence of water.  All of this is a huge hassle but necessary if you want to fly a lot and have a trouble-free engine.

fuel filter damaged by ethanol gasoline

Ethanol also eats away at non-metal parts and stiffen them up which is bad for diaphragm type carburetors.

Fading/stopping near/at full load

This issue is the #1 carburetor adjustment problem that I see in engines which come in here when there is fading/stalling/stopping near or at full load.

This can be caused by an excessive carburetor metering lever (ML) value causing a lean condition or, much less often, a rich condition.  The excessive ML value will cause the engine to stutter/stall when it is at 1/2 or more throttle.  Sometimes, the engine will run just fine for 5 or 10 minutes and then slowly die.  It is similar to an ignition failure.

Most pilots do not check the ML value when they install a new metering lever.  The metering lever adjustment done at the Walbro factory is for diaphragms with a tang on them instead of the much more common button-style diaphragm.  Be certain that your ML is set correctly.  Go to this link for information on how to check and adjust it.  You will have to remove the metering lever diaphragm cover and diaphragm to do this.  It also requires some special tools (available from Harbor Freight).

DO NOT ASSUME THAT NEW CARBURETORS HAVE THE ML ADJUSTED CORRECTLY.  IT MUST BE VERIFIED IF THERE ARE ANY PROBLEMS WITH THE ENGINE.  Remember that Walbro does not make these carburetors for paramotors and will do nothing to help either the manufacturer or the end user thanks to U.S. tort law.

The stock metering lever that is generally available in U.S. kits is adjusted for the tang-type ML diaphragm.  Most diaphragms in the kits that are available to U.S. customers do NOT have the tang and are adjusted to a different value.

TOP 80 ONLY  Fading/stopping near/at full load can be caused by a loose reed valve body in the Top 80 (or any motor that uses the WG-8 carburetor with an internal port to the crankcase), an overlooked problem that must be checked in motors that have fuel pump issues.  Most paramotor engines do not port the crankcase pressure pulses to the fuel pump through passageways in the carburetor and reed valve but do it directly through a fitting on the crankcase and a tube going directly to the fuel pump diaphragm.

Fading at full load may also be caused less often by mechanical and ignition issues – see below.

Hard starting hot

This is usually due to vapor lock in the fuel system.  If any parts of the fuel system get near the exhaust system, the heat can cause vapor lock.  High ambient temperatures also can cause vapor lock.  All gasoline, including AVGAS, will form vapor bubbles if the temperature of the fuel rises past a certain level AND if the ambient pressure on the fuel drops below a certain value.  (Remember Boyle's, Guy-Lassac's, and Charles' gas laws?)

As I note on the fuel/oil specifications page, inexpensive or cold weather gasoline can fizz (begin to form vapor bubbles) if the engine is run during the hotter seasons.  Ethanol blends will fizz more easily and this is just one more reason to stay away from these fuels.  Once vapor lock has occurred, the only remedy is to let things cool off.  Taking a cold water bottle and dumping it over the fuel tank can help get you in the air again.  Once airborne, air movement will help cool things off.

Ordinary general aviation aircraft do not have vapor lock problems because their fuel systems are gravity fed.  Most paramotors have tanks below the engine and fuel must be sucked up which lowers the ambient pressure on the fuel = vapor bubbles or fizz if conditions are hot enough.

C. Ignition Failure

The #2 most common problem is a failure of the secondary ignition system.  Ignition failure will make the engine impossible to start or run.  The ignition system can have a partial failure which makes it difficult to start or cause fading (not stoppage) at or near full throttle.  Ignition problems (other than incorrect timing) will never cause an engine to overheat, thankfully.

Quick ignition test

To get a general idea of the condition of the ignition system, remove the spark plug, reconnect it to the secondary wire, and hold the base of the plug firmly against any metal part of the engine.  (This assumes that the spark plug is intact and has the correct gap.)  Place the paramotor in a darkened area and pull quickly on the starter.  There should be a healthy spark across the spark plug gap and nowhere else.  If pilots want to do a somewhat more thorough check, take a used spark plug and set the gap to +0.045".  Repeat the above test.  The greater gap will insure that the coil and secondary wire have the ability to produce a good enough spark while under load.  If there is a good spark with the greater gap, the ignition system is most likely OK.  This simple test, however, does not check whether the timing is correct or not - a rare situation.

Spark plug

Generally, the first thing we always should do is to check the spark plug gap and/or replace the spark plug if there is any doubt as to its condition.  I am still amazed at the number of engines that come in here which have the spark plug incorrectly gapped, sometimes 50% over specifications.  It is IMPOSSIBLE for the engine to achieve maximum output if the gap is too great or too little.  An incorrectly torqued spark plug will leak and reduce engine output at full throttle.

The Top 80 and Minari have "lawn mower" grade ignition systems which means, among other things, that the spark plug gap on the Top 80 and Minari is unusually small, just 0.020" (0.5mm - 0.6mm).  There will be no spark at full throttle if the gap is too great.  The good news is that on more recent versions of their engines, Miniplane has upgraded the secondary wire assembly.  It only took 10+ years for them to do this....

The plug must be torqued properly and the gap set to the specifications for your motor.  An under-torqued plug will leak, maybe overheat the engine, and the high end performance of the engine will suffer.  A leaking plug will have a black oily mess around the base of the plug.  Be careful not to over-torque the plug as this can destroy the cylinder head.  If the gap is too great, the spark will be quenched at high loads, the engine will misfire, and power will drop.   Always be certain that the spacer-washer is installed with the spark plug (if your engine requires it).  If there is any doubt about the condition of the spark plug, replace it.  Of course, how will you know how many hours the plug has unless you keep a log and have an hour meter/tachometer?

Coil contacting the flywheel

This is a rare problem.  If the coil just brushes the flywheel, it will turn but the flywheel can short out the coil laminations which will affect the spark.  It is easy to see if the coil is touching the coil and the engine does not have to be removed to do the test.  Spray black paint on the outer edge of the flywheel as you rotate it.  On the Top 80, remove the lower two muffler mounting buttonhead screws and you will get a clear shot at the flywheel.  Other engines may require a bit more disassembly from the front.  Let the paint dry and then slowly turn the flywheel by hand or with the starter.  If the coil is too close, it will scrape the paint away.

Simple secondary ignition system test

With a digital multimeter (<$10 from Harbor Freight), measure the resistance from the metal tab inside the spark plug boot to one of the cooling fins on the engine (ground).  It should be 17K Ohms ±10% on the Top 80.  The newer ignition systems on the Top 80 may have a lower value.  For other engines, if you have resistance between 7K and 20K, you are probably OK.  However, if it is open (no resistance), you have a bad secondary wire which must be fixed.  Your options are limited to replacing the wire (easy) or replacing the coil (a difficult and expensive operation).

An internal break in the secondary wire will cause missing and a drop in engine output at high engine loading.  It becomes more acute as the engine heats up and internal pressures increase.  When the break gets sufficiently wide through burning of the ends, the spark cannot jump the gap in the wire, the engine will not start, and the coil may be damaged from internal overvoltage.  Here are more details on testing the secondary ignition wire and replacing it.

If the preceding test is good, place the paramotor in a dark place.  Remove the spark plug.  Reconnect the secondary wire to the plug and firmly push the metal base of the spark plug against any metal part of the engine, like the exhaust pipe.  Pilots who are nervous (me) about getting a shock can use masking tape to FIRMLY hold the plug in place.  THE SPARK PLUG MUST BE GROUNDED OR THE IGNITION COIL CAN BE DESTROYED!  Pull the starter as if starting the motor.  You should see a bright spark at the end of the plug every time the motor makes a complete revolution.

If both of the above tests are OK, continue with the next section.  If not, perform a more detailed ignition system test.  It is easy to do and requires minimal tools.  Engines will never reach full output if there are problems with the spark plug and secondary wire.  Note that too great a coil gap will make the engine hard to start but it will run fine once started.  Do not waste your time tinkering with the carburetor if the ignition system is not working properly.

Kill switch test

If you experience sudden engine failure (not fading), the kill switch circuit could be shorting out.

Top 80, others similar: The green arrow points to the kill switch wire going to the throttle and light blue arrow points to the primary wire that goes to the coil.  Other engines are similar.  These wires are just in front of the carburetor and next to the cooling box.  The engine will stop if the primary wire is grounded.  Sometimes, the wire going to the throttle will break or rub against the Bowden cable and short out.  The switch in the throttle can also be bad.  Separate the connection between the primary wire and the kill switch wire.  Set the multimeter to "Ohms" and its lowest range.  Connect the red lead of the  multimeter to the terminal inside the red boot (others similar) and the black lead of the multimeter to a fin on the engine.  Use some test leads to help unless you have three hands.  The kill switch lead should be "open" – no resistance.  Now press the kill switch a few times.  Each time you press it, the resistance should be less than 3 or 4 Ohms.  If it is any other value, you will need to find out why.  Usually, the wire is either defective or broken.

Top 80 primary ignitiion wire

D. Mechanical issues

Mechanical issues are not anything as common as issues "A", "B", and "C" above.

Note: Few shops have the tools or knowhow to perform mechanical repairs on paramotors, especially adjusting the timing or replacing the ignition coil.  Those who service racing two stroke engines, like dirt-bikes and racing karts, are the best bet.  For example, it takes about $300 of special tools to service every part of the Top 80 correctly.  Thankfully, most pilots will only need a modest tool set that costs much less.

Poor idle

Poor idle can be caused by clutch drag.  You cannot adjust the idle correctly unless the clutch does not drag.  If cheap gasoline is used, run ordinary fuel injector/carburetor treatment through the fuel system.  Pilots would be amazed at how much goo builds up inside a carburetor and effects the idle.

Loose cylinder head

Sometimes, the factory (or pilot) fails to properly torque down the cylinder head.  A more serious cause of a cylinder head loosening is the use of inexpensive gasoline which causes fuel mixture pre-ignition (knocking).  Using ONLY premium gasoline or AVGAS will eliminate the cause of this problem.  However, those who purchase service station premium grade gasoline may not be getting high octane fuel unless it is purchased from major refiners e.g. Chevron, Shell, BP, etc.  AVGAS, a superior (and expensive) fuel, will not cause pre-ignition in any engine as it has the highest octane of all gasoline made other than racing fuels.  Note:  Always put a gallon of premium gas in your vehicle FIRST and THEN fill your portable fuel tank.  You must purge the regular fuel out of the fuel delivery system of the service station.

To tighten the head, remove the cooling air duct/shroud (if present) to access the cylinder head nuts.  Be sure they are torqued to the correct value (e.g. 9 Nm for the Top 80).  Tighten the head nuts in a cross-pattern to the final torque value for your engine.  ALWAYS RE-TORQUE THE HEAD AFTER THE FIRST HOUR OF OPERATION.

Leaks

Check the space between the head and the cylinder for any leaks.  The presence of leaks indicates that the head gasket is faulty and should be replaced.  NEVER REUSE A HEAD GASKET.  I am still amazed at how some DIY's mangle simple things like a head gasket.  Don't risk harming your engine.  If you are going to do your own service, get the necessary parts and tools to do it right.  Engine leaks are common and are rarely serious except at the cylinder and head.  Note: A leak can originate at one point and air passing rapidly over the engine can move the evidence around to somewhere else.

If you think you have a leak, FIRST thoroughly CLEAN the engine THEN run it an hour and see if you can pinpoint the leak.  If the leak is black and gummy, it is a leak AFTER the fuel/oil mixture is burned.  If the oil is clear in color, it is a leak BEFORE the mixture is burned.  For example, leaks between the cylinder and crankcase will have oil that is clear in color because it has not been burned yet.  Leaks between the cylinder and head will always be black in color.  Carburetors on 2 stroke engine will always leak some – it is impossible to prevent.

Compression

Verify engine compression.  All it requires is about a minute of running without oil in the fuel and the engine is ruined.  If compression is low, there are mechanical problems and the engine must be rebuilt.

Carburetor gasket in the Top 80

Sometimes, the gasket between the reed valve assembly and the carburetor will be installed incorrectly on the Top 80 and other motors that use the WG-8 carburetor.  The small hole in the gasket which transmits the pulses from the crankcase must line up with the holes in the reed valve and the carburetor.  This problem will be evident during a thorough test of the fuel system.  The engine may run at low speeds but not run well under load.

Timing and coil gaps

The ignition timing and the coil gap must be correct on all engines.  If the flywheel and coil have not been removed or loosened, these should rarely require any attention or adjustment.  Otherwise, pilots should send their engines to competent mechanics to have these values checked and adjusted if they cannot do it themselves.  These are rare conditions that, ordinarily, will not need to be checked.

Cooling

The cooling system should be checked to be sure there is nothing clogging it.  Some engines do not have forced air cooling, like the Simonini and Minari.  The engine below had a slight problem.

Top 80 engine with debris in the cooling system causing it to overheat

Exhaust problems

Rarely, the exhaust system (muffler) can get clogged.  This will greatly affect engine output, especially at or near full throttle.  Thank you Bill Stoll for this tip.

E. Midrange performance issues (excessive vibration)

This problem is caused by too much fuel entering the engine via the low speed/idle circuit in the carburetor.  It is relatively easy to fix but most do not bother and put up with the roughness and vibration in the midrange.  The higher the altitude where the motor is run, the more annoying the problem.  Here are the instructions on how to fix this.  Having your motor purr in the midrange is a very nice feature, especially if you are flying a "C" class or better gilder which takes much less energy to fly than paramotor wings, especially reflex models.  Having the motor purr at low RPM is a real bonus.  Fixing this problem in the Polini Thor engines makes them the smoothest and quietest engines in the world.

Turkey Vulture

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