paragliding training center
by Had Robinson
Note: Semi-synthetic oils are the best to use if you have any doubts about the gasoline you are using. 100% synthetic oils should be used ONLY according to the instructions below or what the engine manufacturer recommends. Remember that ONLY JASO FD rated oils should be used in paramotors.
Fuel/oil mixture ratios
Top 80 engine -- 2% (50:1) semi-synthetic oil OR 1.5% (67:1) 100% synthetic oil with AVGAS or ethanol-free gasoline
Polini Thor engines -- 2% (50:1) semi-synthetic oil OR 1.5% (67:1) 100% synthetic oil with AVGAS or ethanol-free gasoline
Minari engines -- 2.5% (40:1) 100% synthetic oil with ethanol-free gasoline or AVGAS
Fresh Breeze Simonini 200cc -- 2% (50:1) 100% synthetic oil with AVGAS or premium ethanol-free gasoline
Simonini 200cc -- The factory version of this engine has special fuel and oil requirements because of different tuning than the Fresh Breeze version.
Type of gasoline (in order of preference) CHEAP GASOLINE CAN RUIN ENGINES, ESPECIALLY WHEN RUN AT OR NEAR SEA LEVEL.
1. Aviation gasoline (AVGAS) with
TCP fuel additive or equivalent
2. Aviation gasoline (AVGAS)
3. Unleaded premium gasoline ethanol-free
4. Unleaded premium gasoline with ethanol <10%. Use semi-synthetic oil with ethanol blended fuels.
Premixed racing fuel -- pilots who cannot find AVGAS or ethanol-free gasoline can purchase ready-to-use fuel (includes oil) made by VP Racing Fuels. These fuels are 94 octane and use JASO-FD 100% synthetic oil which makes them compatible with most paramotors. They have 50:1 and 40:1 mixes available. Most major distributors, including Wal-Mart and Home Depot, stock these premixed fuels but they are not cheap. VP Racing fuels contain stabilizers so that the containers can be opened, exposed to the air, and yet 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.
Type of Oil -- semi-synthetic and 100% synthetic oils must have the JASO FD rating. Here are some examples of oils available in the U.S. that have the proper JASO FD rating. Castrol, Lucas, and Motul oils are available from BikeBandit Amsoil oil is sold in most motorcycle shops.
1. 100% synthetic 2 stroke oil: Amsoil
SABER; Bel-ray Si-7 Synthetic 2-Stroke Engine Oil;
Castrol Power RS TTS 2T (best buy,
available online); Fuchs Silkolene Comp 2 Plus Pro 100% synthetic;
Motul 710 2T; Motorex
Cross Power 2-T; Shell Advance Ultra 2; Valvoline
2-Stroke Racing Oil
2. Semi-synthetic 2 stroke oil: Bel-Ray SL-2 Semi-Synthetic 2T Engine Oil; Fuchs Silkolene Comp 2 ester based semi synthetic; Lucas Semi-Synthetic 2-Cycle Oil; Motul 510 2T; Shell Advance VSX 2; Spectro Golden 2T Injector; SynGard Use semi-synthetic 2 stroke oil with ethanol gasoline blends (see below).
Miniplane recommends1 premium unleaded (ethanol free) gasoline for the Top 80, Polini Thor, and Minari models. They recommend premium fuel because of its higher quality rather than its higher octane value.
Unfortunately, it is getting increasingly difficult to find gasoline that is free of ethanol in Europe and North America. Ethanol is the cause of serious problems for the fuel systems in high performance two stroke engines and should be avoided, if at all possible (see below for detailed information on this).
Automotive gasoline that contains ethanol should only be purchased from a major company, like 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 can be used but Miniplane notes that you may have higher running temperatures i.e. you may overheat your engine at higher loads and experience damage.
If you must use low octane/poor quality fuel, increase the thickness of the washer under the spark plug which lowers the compression ratio of the engine and also the running temperature. The latter can be quickly and easily done by adding a second or third washer from a used spark plug to the existing one. 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.
It is important for pilots to note that automotive service station gasoline is formulated differently for the cold and hot seasons of the year. We have learned -- the hard way -- that gasoline refined during the winter months has serious problems with vapor lock when used in hot weather. That is, the fuel may turn to "fizz" inside the fuel system and cause vapor lock. This will starve the engine of fuel and can cause lean-out under high loads which can damage the engine.
Do not use fuel refined in winter for use in the summer. It does not matter whether fuel preservative is used or not. Aviation gasoline (AVGAS), on the other hand, rarely has issues with vapor lock because of its higher vapor pressure and boiling point. Note that most paramotors use a vacuum to pump fuel from the tank to the carburetor unlike other aircraft. This creates a low pressure on the fuel and it is easier for the fuel to reach its boiling point -- and fizz.
If there is any way to use fuel without ethanol, do so. If not, take note of the important precautions below. The engine manufacturers continue to issue warnings about the problems with fuels containing ethanol including the problems with 100% synthetic oils mixing with ethanol blends of gasoline.
WARNING: DO NOT USE GASOLINE WITH MORE THAN 10% ETHANOL. THIS WILL DESTROY THE ENGINE!
1. Semi-synthetic oils ONLY 100% synthetic oils do not mix well with gasoline that contains ethanol. When the mixture sits in the fuel tank, the oil tends to separate out. Simonini notes this problem in their manual for the Mini 2 Plus. Some 100% synthetic oils e.g. Castrol Power RS TTS 2T mix so poorly with ethanol fuels that Simonini will void the engine warranty if those oils are used.
2. Fuel stabilizer Add Sta-Bil or SeaFoam fuel treatment (or equivalent) to help preserve this unstable fuel. Unless Chevron premium gasoline is used, it is helpful to add their Techron additive (or an equivalent) per the recommended amounts. This additive dissolves the gunk that ethanol creates. This additive (or its equivalent) is available at auto parts stores worldwide.
3. Fresh 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 Sta-Bil 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 quickly. It can cause fuel lines 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 so many problems. The metering lever spring inside the Walbro carburetor will weaken from corrosion in the presence of ethanol blended fuels which is why it should be replaced every time the carburetor is rebuilt. The pseudo-scientists who invented the climate crisis have made it worse for all of us -- but what are we to do if we want to live in European-type countries?
4. Carburetor maintenance Regularly test the pop-off pressure of their carburetors because of corrosion and weakening of the pop-off spring caused by electrolysis and/or the presence of water. Miniplane-USA stocks the springs which can be changed out, if your spring appears corroded. Low pop-off pressure dramatically affects high performance due to a richening of the fuel mixture. Rebuild the carburetor as often as needed. Once a year may not be enough.
4. 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. This article from Machinery Lubrication describes what happens when water gets into the fuel.
5. Percent ethanol Test the ethanol percentage in the fuel. For about $10, pilots can buy an ethanol percent tester. 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 will ruin a 2 cycle engine.
6. Air-fuel mixture Be sure that the engine is not overheating. The Walbro Service manual notes that ethanol blends will cause carburetors designed for pure gasoline (the WG8) to run leaner and, therefore, hotter. This is another reason for pilots to install a cylinder head temperature gauge.
ROTAX warns that their engines will experience damage with ethanol fuel blends greater than 5%. This warning from ROTAX should alert paramotor pilots of the problems caused by ethanol. All U.S. blends have 10% or more ethanol. Your region may have more or less ethanol. Be certain to find out what your local blend ratio is.
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 approve the use of AVGAS if anti-lead fouling additives are used, like TCP.
Marine engines and small aircraft engines have much in common. 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.
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 carburetor 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.
Here are some photos of a Walbro 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 right photo, the fuel inlet screen is clogged. This carburetor could not deliver fuel. The pilot was lucky that he did not burn up his engine.
I discussed ethanol fuels with Bel-Ray, a manufacturer of 2-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.
Bottom line: Use gasoline without ethanol.
The piston pictured below seized as a result of a lack of lubrication. The owner of this Top 80 stated that he did not put gasoline without oil 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 this site -> 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.
Unless AVGAS is used, 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. If fuel stabilizer is used, ordinary gasoline can be stored for a year or so (but I never would store it this long).
All service station gasoline (other than AVGAS) deteriorates quickly and loses its octane value after just a few weeks because of oxidation. If you store gasoline, add a fuel stabilizer like Sta-Bil which can keep it fresh for a year in sealed containers. There is also a product from Sta-Bil that is specifically for fuels used in marine (humid) environments called Marine Formula Sta-Bil. If I lived in a particularly hot and humid climate, I would add this special version of Sta-Bil to my fuel if AVGAS was not available.
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
AVGAS may be used in paramotor engines and is preferable to all other fuels because of its high octane, stability, and purity. It also mixes well with all 2 stroke oils. All engine manufacturers note that AVGAS does not harm their engines, contrary to various rumors that circulate on the blogs. In fact, some manufacturers specify that ONLY aviation gasoline should be used in their engines. For example, Nirvana Systems of Czechoslovakia has this in their engine manual:
Solo and NIRVANA recommend using 100% synthetic Castrol TTS in correct oil/petrol mixture, which prevent[s] combustion chamber and exhaust carbonization. Do not store mixed petrol longer than [a] few days, max 2 – 3 weeks. You can mix Castrol TTS with leaded or unleaded petrol. However leaded petrol is preferred. Always use quality petrol.
AVGAS is, by far, the best fuel if your ambient air temperature is over 100 degrees F. However, AVGAS is not available to paramotor pilots in Europe so they must use the ethanol blends -- and suffer the problems of ethanol. Simonini actually warns pilots to use only semi-synthetic oil in their engines but this is because AVGAS is not available -- except in the U. S. and other non-European type countries.
1. It has the highest octane of all gasoline. This, alone, makes AVGAS preferable. The higher the octane, the less damaging pre-ignition there will be in high compression ratio engines, like paramotors. Ordinary automobile fuel oxidizes quickly and, as a consequence, its octane value drops quickly in just weeks during storage.
2. It contains the octane enhancing compound tetraethyl lead. When this compound is burned, it forms lead monoxide deposits which coat various parts of the combustion chamber, especially the spark plug. According to the aviation engine manufacturer ROTAX, lead deposits can damage the crankshaft bearings due to the deposits flaking off and then being sucked back into the crankcase in their multi-piston two stroke engines. This is something that cannot happen in single cylinder paramotor engines. Some claim that ring sticking is more common from the additional lead deposits in AVGAS than from the carbon deposits created by the use of any fuel. There is no proof of this. Ring sticking is caused by cheap oil and/or engine overheating, regardless of whether the fuel is leaded or unleaded. Suffice it to say, overheating is the most common problem in engines which are not properly maintained.
3. It is the most stable of all gasoline and can be stored for long periods (years).
4. It will not cause vapor lock, a serious conditions that causes fuel starvation and can cause an engine to overheat.
5. It will not harm fuel system parts, as does gasoline containing ethanol.
6. Cost is about double that of premium unleaded.
7. It mixes well with all types of 2 stroke oil, especially the 100% synthetic oils.
8. It does cause increased fouling of spark plugs and, to a lesser extent, results in more deposits in the combustion chamber, especially on the top of the piston. This is remedied by the use of approved fuel additives (see below).
Wiki has a long article on aviation gasoline for those who desire to increase their knowledge of engine fuels rather than rely on hearsay and rumor. The dirt-bike and go kart guys laugh at the AVGAS rumors that circulate on paramotor forums. For every PPG pilot there are probably 10,000 bikers and kart racers -- guys who know everything there is about high-output 2 stroke engines. We have repeatedly requested photographs, the affected parts, etc. from the rumor-mill people on the Miniplane blogs but have yet to receive anything. They do not know what they are talking about and should be ignored.
Some airports have given ultralight pilots a difficult time when they ask for AVGAS. It depends where you live. New England is particularly hostile to ultralight aircraft. Private airports can be snarky about anyone and anything. If they have fuel and are close by, take the manager to a $50 lunch and THEN ask him if he can help you. The reason for this is because there are so many irresponsible ultralight pilots and their dangerous antics have made it difficult for the rest of us. You can show your support for responsible and safe piloting of ultralights by joining the USPPA and the USUA.
County airports, however, all receive Federal funds and they cannot legally refuse to sell aviation gasoline for use in an aircraft e.g. in an ultralight. If you are the owner or pilot of any aircraft, you have the right to be in the secure area of an airport where the fuel pumps are. However, it is a waste of time and money to approach the managers of Class A, B, and C airports because you will have to be escorted when inside the secure area or have to apply for an ID. But if that is all I have in my area, I would apply for the ID. Class D and county airports are more relaxed -- in a sense -- and are much more willing to help. County airports often have very helpful, friendly, and knowledgeable managers. Demonstrate to everyone that the safety is your first priority. If possible, get your AVGAS from a county airport. It helps to rent a hangar.
The best thing is to get to know someone who hangars his plane at the county airport and ask him what the general attitude of the manager is towards ultralights. Some can be extremely (and illegally) hostile. Others are reasonable. Your pilot buddy can introduce you to the manager and/or give you a gate combo so you can get in to the pumps.
If you do not know any pilots in the area, dress nicely (many managers are ex-military and are pilots themselves), show up first thing in the morning, and tell the manager who you are and show him your credentials. Do not be defensive -- act like a man, be in control. Go with other pilots, if possible. (You are a member of USUA and USPPA, right?). Explain to them the manufacturer of the engine in your aircraft requires AVGAS and that you keep the aircraft in the back of your vehicle and will need to drive to the pump. Offer him a copy of your driver license, if that will help. For the really rude chumps out there, you may have to appear before your county commissioners and give them the facts. Sometimes a single call from a lawyer will take care of problems. Do not let boorish public officials ruin our sport -- stand up for your rights and the rights of other ultralight pilots who come along.
Where I live, our county airport manager is friendly and helpful to ultralight owners -- but I live in "Red State" territory a.k.a. "flyover country".
If AVGAS is treated with the additive TCP (or an equivalent), the nuisance of lead fouling is eliminated. A quart of TCP (cost <$40 US) will treat 320 gallons. This comes out to about $ 0.13/gal, and is well worth it, considering that less engine maintenance will be needed. The downside is this additive, like all additives, tends to attack the non-metal parts of the fuel system.
Below is a Thor 130 engine with approximately 130 hours of run time. AVGAS was used exclusively in this engine WITHOUT any anti-fouling additives. The cylinder head is nearly 100% free of any lead deposits. Lead deposits do not tend to form on the cooler internal parts of the combustion chamber, like the cylinder head here. The red arrows point to small flakes of lead monoxide that were probably lodged on the edges of spark plug and broke off when the plug was removed. They are soft and harmless in single cylinder 2 stroke engines and are expelled with the exhaust when they break free from engine parts. Note that the spark plug is covered with lead monoxide deposits. Large 4 stroke aircraft engines have expensive spark plugs that get just as fouled as the plug in this photo. On the other hand, our plugs cost a few dollars and are easy to replace.
Here is the same engine with a view of the top of the piston. It runs much hotter than the cylinder head and has more lead deposits. However, even after 130 hours, these deposits are minimal because 100% synthetic oil was used with the AVGAS. If the pilot had used an anti-fouling additive for lead deposits, he probably would not have had to clean the piston. 10 minutes with a razor blade took care of the carbon and lead deposits in this engine.
This is another photo of the same engine as above. Typical in paramotor engines run with untreated AVGAS, the spark plug has the most lead fouling. This plug has about 50% more life before it is worn out but should be replaced because it is badly fouled.
Below is a spark plug from an engine that used AVGAS treated with the TCP additive. The plug is worn out but virtually free of lead deposits. Just prior to this plug being removed, the engine had been idling for a long period which is why the plug has a large amount of black soot on it. Contrary to the spark plugs in multi-cylinder 4-stroke aviation engines, the ones used in the Top 80 cost a small fraction and are easily replaced when fouled. The cooler running temperature of the Top 80 (when properly maintained and tuned) prevents the problems often associated with overheating. If an engine is not properly maintained, it does not matter what kind of fuel is used -- it will experience problems and possible damage.
This spark plug is from an AVGAS burning engine that did use an anti-lead fouling additive. Note that the fouling is only present close to the grounded electrode and absent from the cooler parts of the plug. The cylinder head had no lead deposits and the piston had minimal deposits. The only symptom the engine had was hard-starting because the plug is worn out. Lead deposits can be eliminated by the correct fuel additive (TCP). Engines that use ethanol blends will not last as long and why any other kind of fuel is preferable. Regardless of what kind of fuel is used, the spark plug will wear out and/or foul. It is so inexpensive to change out the spark plug and improve starting and high end performance.
Here is a plug from a Polini Thor 130 used for tandem flying. AVGAS treated with the TCP additive was used exclusively in the engine. It has about 30 hours on it and is at the end of its life. Even so, the plug has very light fouling. The cylinder head and piston crown will have little if any fouling. Compare the plug below with the plug above. Both engines had about the same number of hours on their respective plugs. It shows what a difference the TCP fuel additive makes.
Below is a photo of an EGT sensor that has a small coating of lead monoxide (light yellow in color) from the burning of AVGAS without the TCP additive. It is a harmless powdery substance and is easily removed with a wire brush. As with carbon deposits, the lead deposits must be removed periodically from the top of the piston and cylinder head, along with the carbon deposits. This is necessary to help the engine cool more efficiently.
Running any engine too hot (lean conditions) will cause the lubricating oil to burn at the lands, including the sides of the piston, due to piston overheating, regardless of what kind of fuel is used. This creates the black gummy deposits which can bind the ring.
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 coating the surface of the piston. 100% synthetic oil can get much hotter than other types of oil before it will burn (oxidize) and why this type of oil is preferable to others. 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 caused by a sand grain getting sucked into the engine and then caught between the cylinder and the piston.
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. Lead deposits from AVGAS are not black and gummy but light yellow.
Note: Miniplane has updated (as of July 2016) their requirements recently due to changes in gasoline blends throughout the western world i.e. the increased use of ethanol. Other manufacturers continue to update their requirements so check this site often.
Thor and Top 80 --Semi-synthetic 2-cycle oil at 2% mix (50:1 ratio) with all types of gasoline. 100% synthetic oil at 1.5% mix (67:1) but only with ethanol free premium gasoline or AVGAS. Miniplane has reported that using 100% synthetic oils at the 2% mix ratio may cause engine overheating.
Minari -- 100% synthetic oil at 2.5% (40:1) AVGAS or ethanol free fuel only
Fresh Breeze Simonini Mini 2 Plus -- 100% synthetic oil at 2% (50:1) AVGAS or ethanol-free fuel only
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.
Higher mix ratio -- Miniplane allows a 1.5% mix (67:1) for the Top 80 and Thor models if 100% synthetic oil only is used. However, do not use gasoline containing ethanol at the higher mix ratios. You must use either AVGAS (preferably) or premium unleaded that has no ethanol in it.
The brands of oil Miniplane recommends for a 1.5% mix are not available in
the U.S. However, the recommended brands all have the
JASO FD rating. 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.
These oils have the required JASO FD rating. DO NOT USE OIL THAT IS NOT JASO FD RATED.
Bel-ray Si-7 Synthetic 2-Stroke Engine Oil
Castrol Power RS TTS 2T (must never be used with ethanol blends)
Fuchs Silkolene Comp 2 Plus Pro 100% synthetic
Motul 710 2T
Motorex Cross Power 2-T
Shell Advance Ultra 2
Valvoline 2-Stroke Racing Oil
Semi-synthetic oils that have the required JASO FD rating. The semi-synthetics are considerably less expensive than the 100% synthetic oils.
Bel-Ray SL-2 Semi-Synthetic 2T Engine Oil
Fuchs Silkolene Comp 2 ester based semi synthetic
Lucas Semi-Synthetic 2-Cycle Oil
Motul 510 2T
Shell Advance VSX 2
Spectro Golden 2T Injector
SynGard (this oil is hard to find)
The best 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.
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 causes 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 just what the manufacturer specifies.
Per Miniplane's recommendation 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. 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 always fresh.
1Miniplane's website is not set up like most. To view their fuel and oil recommendations, click on this link, then "engine" on the left, and then "mixture" at the top.