Fuel and Oil Specifications for two stroke paramotors
by Had Robinson.
Updated December 28, 2021
Continued testing over many years requires updates of this page. A year test of AVGAS at sea level in a 130cc paramotor yielded some surprising results. A good introduction to gasoline is on this U.K. web site that discusses fuels used in gasoline engines.
Fueling equipment You will need the right equipment to mix, store, and transfer your fuel. Please see the equipment page for more information. It is not so simple as most think. Metal containers are the best for storing gasoline because, unlike plastic, UV from sunlight cannot penetrate metal. UV and oxygen cause gasoline to *deteriorate* quickly. If you do use plastic (HDPE) containers, especially clear ones, store them in a cool, dark place and never in direct sunlight. It is wise to put labels with the date, mix, and type on fuel containers in order to prevent disasters.
A. Quick reference
Use full synthetic oils. In the U.S. these oils are widely available:
AMSOIL Dominator Synthetic 2-Stroke Racing Oil
Motul 800 2T or 710 2T Synthetic 2-Stroke Oils
Top 80 engine – 2% (50:1) full synthetic oil with premium ethanol-free MOGAS
Polini Thor engines – 2% (50:1) full synthetic oil with premium ethanol-free MOGAS
Minari engines – 2.5% (40:1) full synthetic oil with premium ethanol-free MOGAS
Fresh Breeze Simonini 200cc – 2% (50:1) full synthetic oil with AVGAS (Fresh Breeze specifies that only AVGAS be used in their engines)
Simonini 200cc – The factory version of this engine has special fuel and oil requirements because of different tuning than the Fresh Breeze version.
Vittorazi Moster 185 – 2.5% (40:1) full synthetic oil with premium ethanol-free MOGAS
- Unleaded premium gasoline ethanol-free – The U.S. EPA requires that all automotive
gasoline formulas have a lower vapor pressure (< 9.0 psi/62kPa) during the warmer months (May 1 - September 15) in order to lower smog
levels. (Some states have greater requirements
e.g., California.) Unfortunately, during the colder times of the year, there are no EPA maximum vapor pressure requirements. This means that fuel in a negative pressure
system (typical of nearly all paramotors) will have a greater tendency to form vapor bubbles that often causes a sudden stall or fading due to
vapor lock. It is most common when at idle or at full throttle. Pilots will have to decide whether their
paramotors can tolerate the higher vapor pressure of the gasoline used during the colder season. They may have to use premixed racing fuel.
- Unleaded premium gasoline with ethanol <10%. If you must use fuel with ethanol, follow the instructions below.
- Premixed racing fuel – Pilots who cannot find ethanol-free gasoline can purchase ready-to-use, pre-mixed fuel made by VP Racing Fuels. These fuels are 94
octane and use full synthetic oil. They have 50:1 and
40:1 mixes available. Most major distributors, including Wal-Mart and Home Depot, have these premixed fuels but they are not cheap. VP Racing fuels contain stabilizers
so that the containers can be opened, exposed to the air yet, according to the manufacturer, the fuel will remain fresh for a year. Accordingly, additives are used to prevent
the deterioration of the oil that has been mixed with the gasoline. These fuels are probably the finest that can be used in any two stroke engine.
- Aviation gasoline – We no longer recommend using AVGAS in paramotors. The problem of using AVGAS in paramotors is that the lead deposits can foul the lands on the piston resulting in ring sticking. This is less of a problem when operating at high altitudes (>4,000' MSL) but can be severe at sea level and in hotter climates. The addition of fuel additives e.g. TCP can lessen the problem but does not eliminate it. We have discovered this from thorough testing at various altitudes and climates.
Exxon Mobil has this primer on gasoline storage. Cheap or old gasoline can ruin engines, especially when run at or near sea level where engines run hotter. Make certain that the gasoline is fresh (less than 30 days old). Exxon Mobil, for example, notes that gasoline can be stored for up to (6) months but it is not easy to meet the storage requirements, mainly keeping oxygen away from the fuel. Fuel preservative helps but it is still better to have everything fresh.
Our shop has boxes of burned out engines, many of which were ruined because of cheap/old fuel and water contamination. Water-saturated ethanol fuels will cause erratic engine performance because of different stoichiometric requirements. Paramotors are closest to chainsaws in design and carburetion. Unfortunately, paramotors experience vapor lock more than any other type of internal combustion engine because of the fuel tank being far below the engine.
Honda has this quick reference on how to avoid fuel problems.
Chevron published this technical document on motor fuel which is helpful for those wishing to improve their knowledge of fuels rather than rely on hearsay and rumor of which there is way too much in the paramotoring community.
EXXON has these words on the lack of quality control in MOGAS and why pilots should only by fresh gasoline from major suppliers:
Note that properties critical to aviation use (for example, vapor pressure and cleanliness) are not controlled to the same degree in automotive motor gasoline manufacture and handling. ExxonMobil aviation does not support or approve the use of Automotive Gasoline as aircraft fuel. (from their page on AVGAS)
Types of gasoline
1. Premium ethanol-free automobile gasoline
High quality premium ethanol-free gasoline is a good choice because it burns with the least amount of deposits but only if it is fresh (<30 days old) or properly preserved and stored. It does not add lead to the atmosphere. Briefly, all automotive gasoline (MOGAS) will start to decay when it comes in contact with oxygen. Stored properly, MOGAS can last about (6) months but longer with additives, like Sta-bil. How old is the fuel at the pump? High volume stations will have fresher fuel. But, you will never really know. (Please see "Fresh fuel only" below for more information on this.) Modern automobiles will run on just about any concoction of unleaded gasoline and other chemicals, even fuel that is months old.
MOGAS winter formulas, including premium grade, have more volatile and cheaper components that cause the gasoline to form vapor bubbles a.k.a. vapor lock when the negative (suction) pressure pulls the fuel up from a partially empty tank. It can be so severe that the engine will stall or only run at idle or less than 1/2 throttle. Pilots who experience fading or stalling of the engine during winter months may have to use racing fuel (see below). Southwest Airsports has developed the FSM to counteract most of these problems. Some states require the same quality (and vapor pressure) year around e.g. California. MOGAS summer formulas required by the EPA begin May 1st and end September 16th.
ROTAX notes these important points about why pilots should use only premium fuel from a major (and busy) supplier and why a high octane value is needed. Gasoline with a high enough vaporization pressure to make it compatible with the negative fuel system pressure in all paramotors (except the Fresh Breeze) is more likely to come from a major supplier.
- First, when fuel is premixed with 2-stroke oil, the octane rating is reduced by about 2 points. An 87 octane fuel would therefore become 85 octane.
- Second, fuel evaporates and loses its octane rating when it lays in your ultralight’s fuel tank or in a plastic jug. A “premium”, 91 octane fuel will see its octane rating reduced to unusable levels after as little as three weeks. Fuel with a lower octane rating would obviously have an even shorter usable life.
2. Automobile gasoline with ethanol
Many (2) stroke engine manufacturers continue to issue warnings about the problems with fuels containing ethanol. Ethanol is a powerful solvent and attacks soft fuel system parts. It also attracts moisture which can cause corrosion of metal parts and leans out the air/fuel mixture. Ethanol also lowers the vapor pressure of gasoline and increases the problem of vapor lock in hot weather.
Almost all paramotors use various models of the Walbro diaphragm carburetor and they warn about the potential damage caused by ethanol in gasoline.
The simple fact is, ethanol in gasoline can damage Your fuel system. Gasoline which is organic will begin to decay due to high amounts of oxygen in fuel containing ethanol. Ethanol containing fuel will also absorb moisture from the air because ethanol is hygroscopic and will attract moisture. This added moisture can lead to phase separation. With phase separation comes corrosion to critical engine and fuel system components. The fuel system can also be impacted by contaminants carried in the gasoline itself, as well as gasoline containing ethanol. When used in mowers and other power equipment, ethanol can lead to higher operating temperatures, erratic running, and engine-part failure.
The bottom line is that those who use ethanol fuels must also use fuel additives that help preserve the gasoline and lessen the damage caused by moisture in the fuel. If you must use ethanol fuels, be sure to add the correct additives to help lessen that damage (see below).
Mercury Marine has this to say in their owner's manual for the OptiMax 135 HP outboard:
Water in the fuel system clogged the carburetor (photo below) fuel inlet screen and made it impossible to start or run the engine. After the saturation point with water is reached, additional water remains separated from the fuel. When it reaches the inlet filter screen in the carburetor, it takes 30-60kPa (5-10 psi) to move it through the screen. That is, the water acts as a dam to fuel in the system.
Automotive gasoline that contains ethanol should only be purchased from a major company, like Exxon, Esso, BP, Chevron or Shell, because their fuels contain important additives, especially detergents, that lessen the buildup of carbon inside the cylinder and gunk in the fuel system caused by the presence of ethanol. Lesser grades of fuel than premium can be used but you may have higher running temperatures i.e. you may overheat your engine at higher loads and experience damage.
NEVER USE GASOLINE WITH MORE THAN 10% ETHANOL.
Here is a water (and debris) clogged inlet filter screen of a carburetor and fuel system that had become saturated with water. Fuel was unable to pass through the filter preventing the engine from running.
Observe these precautions when using ethanol fuels:
- Fuel stabilizer Add Sta-Bil, SeaFoam, or an equivalent
fuel treatment to keep the fuel fresher. Unless Chevron premium gasoline is used, it is helpful to add their Techron additive (or an equivalent) periodically. It does an amazing job
cleaning the fuel system of gunk and other residue.
- Fresh fuel If you are using premium (as you should), did you pump a gallon into your vehicle first? If you do not do this, the fuel in your portable tank
could be 50%
regular grade fuel. Do NOT allow gasoline with ethanol to sit for more than a month in
the fuel system as it can damage the metal and non-metal parts of the engine. If fuel stabilizer is
used, blends can be stored in ordinary gasoline containers for many months IF NOT
MIXED WITH OIL. If pilots store
motors for more than a few
weeks, they should purge the fuel lines and carburetor. Ethanol is a powerful solvent that causes non-metal fuel system parts (tubing, gaskets,
diaphragms, filter material) to deteriorate. It can cause some makes of fuel line to swell enough to allow the pickup tube filter in the fuel tank to fall off. Ethanol is hygroscopic and
also conducts electricity. This causes electrolysis of the metal parts in the engine and is why those using two stroke engines in a marine environment have endless problems. The
metering lever spring inside the carburetor can be affected from corrosion in the presence of ethanol blended fuels (which is why it should be replaced every time the carburetor is rebuilt).
Remember that fresh fuel (< 30 days old) is always better than old fuel, even when stabilizer is used.
- Carburetor maintenance Regularly test the
pressure of your carburetor because of corrosion and weakening of the
pop-off spring caused by electrolysis and/or the presence of water that is mixed with the fuel. Testing the pop-off and, more importantly, the rest pressure is the only way to tell if the spring or ML valve seat is bad. Miniplane-USA stocks the
springs. Low pop-off pressure dramatically affects
the high-end output of an engine due to a richening of the fuel mixture. High pop-off pressure is usually caused by water in the fuel. Rebuild the carburetor often.
- Water contamination Check that the gasoline does not
contain either water (mixed in with
the ethanol) or more
than 10% ethanol. Wiki has a good
article on the stability of gasoline, especially ethanol mixes, and what happens as these mixes age.
- Percent ethanol Test the ethanol percentage in the fuel with an
percent tester. The fuel sampled here contained exactly 10% ethanol.
If 10% ethanol fuel contains water the fuel tester will indicate an ethanol content <10%. This is another reason why pilots who live in humid parts of the world should not use ethanol fuels in their engines unless they are certain that it is not contaminated with water. For example, if you test fuel that is supposed to contain ethanol and the tester shows it to be ethanol free, the fuel has been fully saturated with water. Such fuel can ruin a 2 stroke engine.
- Air-fuel mixture Be sure that the engine is not overheating or running too rich. The Walbro Service manual notes that ethanol blends will cause carburetors designed for pure gasoline (like the WG8 and WB37) to run leaner and cause the engines to run hotter. This is another reason for pilots to install a cylinder head temperature gauge. Ethanol fuels require less oxygen than the same quantity of pure gasoline. This means that ethanol fuels may require different carburetor jetting i.e. a larger main jet size. This aspect of ethanol fuels is largely ignored.
Here are some comments on gasoline with ethanol from the engine and carburetor manufacturers:
Briggs & Stratton
We DO NOT recommend the use of gasoline which contains alcohol, such as gasohol. However, if gasoline with alcohol is used, it MUST NOT contain more than 10 percent Ethanol and MUST be removed from the engine during storage. - Owners Manual series 90100 (small engine)
Recreational Power Engineering, the U.S. distributor of the 2 stroke Hirth engines, has these recommendations on fuel and oil for the Hirth engine. They warn against using ethanol fuels and synthetic oils in humid environments. They allow the use of AVGAS if anti-lead fouling additives are used, like TCP or Decalin RunUp. However, our testing of AVGAS has caused problems in some engines, especially larger engines with high hours.
MarineMechanic.com has this informative article on coping with the poor quality gasoline we have to use these days. They emphasize the importance of additives and making sure the engine is tuned up correctly and have advice on how to reduce carbon buildup inside the engine.
Moeller Marine Products, manufacturers of fuel system components, has this warning,
Ethanol is a common additive to blend the fuels with, and while ethanol may not pose the environmental hazards of other gas additives, the chemical properties of ethanol have the potential to cause severe damage to engine systems.
Walbro, the manufacturer of the (obsolete) carburetors used on Miniplane engines, warns users in this video about using ethanol blended fuels and how to prevent damage to the carburetor and fuel system.
Bel-Ray I discussed ethanol fuels with Bel-Ray, a manufacturer of two stroke motorcycle racing lubricants. They noted that their oils mix correctly with ethanol fuels but warn users that the fuel must not have ethanol >10%.
FRAM, a manufacturer of filters, warns users not to use ethanol fuels that have more than 10% ethanol because it will damage their filters.
Poulan, a chain saw manufacturer, warns of the serious problems caused by blends with ethanol >10% or which have been contaminated with water.
Seastar Solutions, a major manufacturer of marine fuel system parts, warns owners to replace their fuel filters every 50 hours or once a year because of the effects of ethanol in gasoline. They also warn owners that ethanol causes deterioration of fuel system lines, making them hard and brittle from the inside out.
Below are some photos of a carburetor that stopped working due to water and gunk from gasoline with ethanol. In the left photo, water and gunk covers parts of the fuel pump diaphragm. The pump could not do its job. In the bottom photo, the fuel inlet screen is clogged. The internal fuel pump in this carburetor could not deliver fuel. The pilot was lucky that he did not burn up his engine.
The piston pictured below seized as a result of a lack of lubrication. The owner of this Top 80 stated that he added oil to the gasoline in his motor. The likely explanation is that the ethanol fuel had been contaminated with water, causing the lubricating oil to separate out. Chris Barker of Royal Purple synthetic oils confirmed in a telephone call to me that water contaminated ethanol fuels will do this.
To find sources of ethanol free fuel, go to http://pure-gas.org. If you find ethanol-free fuel at a service station, check it before filling up as it may be mislabeled. Unfortunately, ethanol free fuels are becoming more difficult to find.
3. Aviation Gasoline
AVGAS has some advantages. It is the purest, the most stable, has the lowest vapor pressure, stores indefinitely, and has the highest octane of any commonly available gasoline.
However, the lead deposits it creates may cause serious problems. Other paramotor mechanics have noted that ring sticking is more common when AVGAS is used. We just recently confirmed this in tests run on a 130cc engine at sea level during the last year (2021). Interestingly, the same engine run at high altitude (4k' MSL) did not experience ring sticking over many years. This is probably because engines at sea level run hotter which may contribute to the deposit problem but this is only a speculation. Also, this engine had high hours which may have contributed to the problem.
Below is a piston from the test engine that has parts of it which are coated with lead phosphate (light gray in color). The AVGAS had the TCP additive which greatly helped with deposit fouling – but it was not enough. The rings were stuck on one side and were difficult to remove due to the migration of the deposits into the lands. As the engine ran, the problem worsened. The sticking piston rings allowed blow-by of the burnt fuel (clearly shown in the photo below). It took over an hour to remove the deposits. There was at least a full teaspoon of lead phosphate that was scraped and brushed off. The decompression port in this engine also had some minor deposits but were easy to clean.
Despite the many advantages of AVGAS, the issue of lead deposit fouling in some paramotor engines makes it a last choice. 100LL AVGAS was engineered to be used in 4 stroke engines, not 2 stroke which has a different method of lubricating the cylinder walls.
Pilots who use AVGAS will have increased routine maintenance (deposit removal from the cylinder head and piston). However, if you fly at high altitudes, the lead deposits may not be an issue. Larger engines and engines with high hours may also be more susceptible to fouling.
If AVGAS must be used, add fuel treatment. If treated with the additive TCP or Decalin RunUp, the problem of lead oxide fouling is not nearly as bad. A quart of TCP (cost <$40 US) will treat 320 gallons. A quart of Decalin (not "certified" for aviation use) costs $35 and will treat up to 640 gallons, depending on the engine. For TCP, this comes out to about $ 0.13/gal and $0.05 for Decalin). For info on how TCP works, read this pamphlet from Alcor. The active chemical in these additives is known as a lead scavenger. During combustion, the tetraethyl lead is converted into lead phosphate instead of lead monoxide. Lead phosphate is a non-conductive compound that does not foul spark plugs (or short them out, as I experienced one time). Rather than build up on the piston and spark plug, nearly all of the lead phosphate is carried harmlessly out in the exhaust stream in most engines but not as much in paramotors for some reason.
Additionally, it would be a good idea to inspect engines using AVGAS more often e.g., every 50-75 hours. Fouling of the rings and lands is easy to see if the exhaust system is removed, exposing the piston.
Use of poor quality fuel
Cheap fuel has all sorts of problems, including widely varying quality, lack of cleanliness, high vapor pressure, poor quality control in summer/winter formulas, and the presence of contaminants, especially water. ONLY USE GASOLINE FROM MAJOR REFINING COMPANIES IN YOUR PARAMOTOR.
If you must use low octane/poor quality fuel, add another spacer washer under the spark plug. This will lower the compression ratio and running temperature of the engine (horsepower will also decrease slightly). If you get too much spacing, you will not harm anything except lower the engine output. The special aluminum spark plug spacer washers (2mm) are available from Miniplane-USA. Poor quality fuels will also vaporize (form bubbles) in the fuel system more readily which will lean out the air/fuel mixture. The carburetor pump will stop working if there are too many vapor or air bubbles in the fuel.
Winter vs. summer gasoline formulations
It is important for pilots to note that automotive service station gasoline (MOGAS) is formulated differently for the cold and hot seasons of the year in most states in the U.S. and in foreign countries. We have learned – the hard way – that gasoline refined during the winter months has problems with vapor lock. That is, the fuel can turn to "fizz" (bubbles) inside the fuel system and cause vapor lock. It is especially noticeable when going to idle while flying when a bubble in the fuel stream will stall the engine. Vapor lock will starve the engine of fuel and can cause lean-out under high loads, which can damage the engine. Therefore, it is a good idea not to use fuel refined in winter for use in the summer. It does not matter whether fuel preservative is used or not.
This video of fuel vapor bubbles forming forming in gasoline when a vacuum head of about 3' (1m) demonstrates the inherent problem in gasoline subject to negative atmospheric pressure i.e. being sucked rather than pumped out of a fuel tank. (This is why small aircraft have ONLY gravity fed fuel systems.) This can be done first hand by using a jiggle-siphon to move fuel from an elevated tank to another tank 3' below. As the fuel is rapidly moving through the siphon tube, jam the jiggle valve against the bottom of the upper tank and you will see a sudden appearance of bubbles in the siphon tube. This is caused by a negative pressure in the tube which causes the fuel to vaporize and form bubbles. These bubbles in the fuel system will stop the movement of fuel through a carburetor. This video of fuel vaporization in a running engine prevented it from achieving full throttle.
Fresh Fuel ONLY
Honda Motor Co. has these words about the importance of fresh fuel,
Fuel deterioration and oxidation can occur in as little as 30 days and may cause damage to the carburetor and/or fuel system. ...Deteriorated gasoline will cause hard starting, and it leaves gum deposits that clog the fuel system. If the gasoline in your engine deteriorates during storage you may need to have the carburetor and other fuel system components serviced and replaced. ...You can extend fuel storage life by adding a gasoline stabilizer that is formulated for that purpose, or you can avoid fuel deterioration problems by draining the fuel tank and carburetor. – from the 2011 Owner's Manual for the GX120, GX160, and GX200 engines
Be certain that fuel is fresh (less than 2 weeks old is best). Those who live in humid climates must exercise much greater care when using fuels mixed with ethanol because of the hazard of water contamination. Typically, water contamination occurs when humid air enters a fuel storage tank through the main vent. As the barometric pressure lowers (e.g. from a storm) water in the air will condense on the wall of the tank and wind up at the bottom – and eventually into your engine. If fuel stabilizer is used, ordinary gasoline can be stored for a year or so (but I would never store it this long).
Here is what MOGAS looks like after a small amount of it was stored for a few months in an ordinary gas can. The gas can was less than 1/2 full i.e. there was plenty of air (oxygen) available to oxidize the fuel. Fuel stabilizer was not used. Fresh gasoline is as clear as water.
Sticking piston rings
Running any engine too hot (lean conditions) will cause the lubricating oil to burn at the lands, including the sides of the cylinder and piston, due to piston overheating, regardless of what kind of fuel is used. This creates the black gummy deposits which can bind the ring. Red Line (a two stroke oil manufacturer) notes this in one of their technical documents.
This piston came from a fuel starved engine which overheated. Even though unleaded fuel was used, the piston was hot enough to burn the lubricating oil that is on the surface of the piston. The piston ring was stuck in the lands due to the burnt oil. The pilot flew this engine at the beach. The long vertical gouge was probably caused by a sand grain getting sucked into the engine and then caught between the cylinder and the piston. If the pilot had used 100% synthetic oil there would not have been as much damage.
AVGAS, unfortunately, can foul the lands under some conditions and why we no longer recommend it. Those who fly at high altitudes have less, even no trouble with this because engines run much cooler, in general.
Cheap fuel/oil, old fuel, and/or ethanol fuels contaminated by water will leave damaging deposits that can find their way into the piston ring and cause it to stick. Another problem with the cheap oils is that they tend to rapidly clog the decompression port, if present, on 2 stroke engines.
C. 2 STROKE OILS
Increasing the oil mix ratio Increasing the amount of oil in the gasoline above the manufacturer's recommended value does not prolong the life of the engine. Increasing the oil mix increases the viscosity of the mix and, as a result, leans out the fuel mixture which can cause overheating. Oil also burns hotter than gasoline. Outboard motor manufacturers (e.g. Evinrude, Johnson) recommend increasing the oil mix in new engines. Why not in paramotors? This is because an outboard is water cooled and is virtually impossible to overheat. This is unlike an air cooled engine which are used in most paramotors. However, some paramotor manufacturers specifically recommend increasing the oil mix ratio in new engines. They have engineered the engine so that it can withstand the additional heat generated by the increased oil mix. If your engine manual does NOT specify increasing the oil mix, don't. In generally, follow the directions in your engine's manual and ignore the fruitcakes, the AH's, the jerks, the bloggers and others who claim to have "special knowledge" about fuel and oil.
Type of oil – I no longer recommend using semi-synthetic oils in paramotors. Use a 100% full synthetic oil, such as Amsoil's Dominator, which is more resistant to the effects of heat. Overheated oil cannot lubricate. The piston below (inside view) shows what happens to cheap oil when things get hot. The black gunk will also get in the piston lands and cause the rings to stick – and ruin the cylinder wall.
When the cylinder wall temperature exceeds 180ºC, the lubricating properties of ordinary oil begin to deteriorate. It is one of the most important reasons to use 100% synthetic oils.
This page from NTN of Japan has information on lubricants for roller bearing that is helpful for PPG pilots.
2 stroke oils:
- Amsoil DOMINATOR 2-Stroke Racing Oil (most motorcycle shops)
- Bel-ray Si-7 Synthetic 2-Stroke Engine Oil (eBay and others)
- Fuchs Silkolene Comp 2 Plus Pro full synthetic (hard to find in the U.S.)
- Motul 800 2T or 710 2T (most motorcycle shops)
- Motorex Cross Power 2-T (most motorcycle shops & eBay)
- Red Line 2 Stroke Racing Oil (eBay and others)
- Shell Advance Ultra 2 (hard to find in the U.S.)
You have a $6,000 paramotor and you want to save a few bucks on oil? Does this make sense? Racing oils are not to be used on public highways because they don't burn 100% so pollute more but they are the best oils.
1. Miniplane Thor and Top 80 engines – Full synthetic 2-cycle oil at 2% mix (50:1 ratio). Miniplane has reported that using full synthetic oils at the 2% mix ratio may cause engine overheating under certain conditions i.e. running at full throttle for extended periods. Therefore, it is a good idea to keep an eye on your CHT while running the engine.
Higher mix ratio – Miniplane allows a 1.5% mix (67:1) for the Top 80 and Thor models if full synthetic oil only is used. The brands of oil Miniplane recommends for a 1.5% mix are not available in the U.S. Why use the lesser oil mix? Engines using the 1.5% mix will run cooler and more efficiently because of the lower viscosity of the fuel mix. In addition, the lower ratio has less negative impact on the octane value of the fuel. That is, the addition of oil to the fuel mix lowers the octane value of the fuel. Lowering the octane of the fuel can cause overheating and pre-ignition. I have observed that the 1.5% mix results in a smoother running engine and a small improvement in power output but I would be careful and use only the finest oils if using this ratio.
If you do use the 1.5% ratio, do not use gasoline containing ethanol. You should use premium ethanol-free unleaded.
2. Minari – Full synthetic oil at 2.5% (40:1)
3. Fresh Breeze Simonini Mini 2 Plus – Full synthetic oil at 2% (50:1) AVGAS only. Fresh Breeze recommends that pilots use Castrol TTS oil. However, Castrol TTS oil is not recommended by some engine manufacturers because this 100% synthetic oil does not stay mixed in unleaded gasoline containing ethanol. Our own tests with the oil demonstrate that it mixes well with AVGAS. Our own experience with this oil is that it can be hard to find at times in the U.S., to say nothing of the controversy surrounding it.
4. Simonini Mini 2 Plus – The factory version of this engine has special fuel and oil requirements because of different tuning than the Fresh Breeze version.
5. Vittorazi Moster 185 – 2.5% (40:1) full synthetic oil with premium ethanol-free MOGAS
Fuel oil ratio
A good mixing bottle is from Shoreline Marine and is sold by Sports Academy and others. It is simple, well marked, and can be sealed to keep dirt out.
Some mix their fuel at a lesser ratio than the recommended 50:1 for the Top 80, e.g. 40:1, thinking that it helps lubricate engine parts better or is necessary when breaking in a new Top 80. Both Miniplane and Polini warn against this practice as it can damage an engine due to the increased fuel mixture viscosity which can lean out the fuel/air mixture and overheat the engine. Always be sure to follow the recommendations of the engine manufacturer. Pilots have to resist rumors and hearsay and stick to the engine manuals and information from well-researched sources, like this web site. Note that outboard motors are water cooled and will not overheat.
Here is a discussion of what can happen when lower fuel oil ratios are used in engines where this is not recommended. It will lean out the fuel burn and can foul the combustion chamber, including the piston ring, regardless of the type of gasoline used.
Minari has this note in their user manual, "WARNING: Please note that an excessive amount of oil does not stretch the life of the engine. a wrong quantity of oil leads to seizure." That is, too much oil in the gasoline can cause overheating in some engines.
Polini has this note in their user manual for the Thor engines, "...mixes that contain too much oil do not extend the engine’s life."
Everything depends on how the engine is engineered and the jetting used in the carburetor. Do not experiment with the fuel/oil ratio but do exactly what the manufacturer specifies. See this page on labeling fuel containers properly which can help prevent a disaster.
Mix the oil just before use
Per Miniplane, other paramotor manufacturers' recommendations, and the experience of many pilots, it is always best to mix small quantities of oil and fuel just before use and not store the mix more than (2) weeks no matter what kind of gasoline is used. The lubricating properties of the oil are affected by long term contact with any kind of gasoline, with fuel additives, and especially with ethanol blends. I mix fuel and oil (2) gallons at a time. It is a nuisance but it means my fuel mix is fresher.
Here is some good advice from Vittorazi (please excuse their poor English),
A mixture that has been prepared from 2-4 weeks and left in a tank, could separate the oil from the gasoline, losing the characteristics of lubrication even if shaken before the use. Avoid to prepare big quantities of mixture, when you are already conscious to use only a part of it.
Always fly safely and courteously.