Fuel:oil premix chat


Well-Known Member
Local time
8:05 AM
Nov 9, 2007
Duvall, WA
There is so much info and misinformation on the web about 2-T (2 stroke, 2 cycle) fuel/oil premix, it often leaves my head spinning. I've attempted a short snapshot to start a discussion, question and answer session, so to speak, on the subject of normal pump gasoline and oil premix. For the sake of this discussion I'm sticking with normal fuel and commercially available oils. Alcohol, nitromethane, home brewed oils an other exotic fuels and oils can be discussed at a different time.

Please feel free to ask, challenge, present data, record your experiences and anecdotes.

Fuel/Oil Mix Ratio

What is THE correct ratio? It depends. Next subject. OK, just kidding 16:1, 20:1, 25:1, 30:1, 32:1, 40:1, 50:1, 70:1, 80:1, 100:1 - what do these all have in common, beside the obvious? They all are ratios I have recommend in the last year. So which ratio is correct? The one that meets your needs. If you don't know your needs, you can find a logical starting point, this leads us to a good place to start the discussion.

Engine manufacturer vs. Oil manufacturer

This can be the best starting point. Engine builder says 30:1. End of conversation? Oil blender says 50:1. Stuck already......I guess I'll go with 40:1! Now I have three choices.....head spinning....

This is usually discussion battle royal, no holds barred....with the winner usually being the engine builder. When you read a 2 stroke owner's manual, they normally do not say "follow the instructions of the oil manufacturer" at least none of mine say that. They give you specific oil ratios to use and warn that deviating from these might result in damage. No matter what the oil, mix it at this ratio - but the main problem with this, oil brands vary a lot. Some can be run more dilute than others, because they have a heavier base oil, totally different additive packages. Not all oils should be diluted the same. So is the oil company always correct? 100:1 for everything using this oil? Of course NOT. That's exactly why some oil manufacturers make different kind of oils for different engines. On the other hand, the oil manufacturer does not know WHAT brand oil is going into the engine. (I won't bog this down with 2 stroke oil standards, such as TC-W3, or loosely followed and often outdated standards such as ISO-L-EGD, JASO FC and FD, API TC that's a whole other can of worms)

The problem with both these above approaches, is that they leave out many important variables. The most important beside engine design and oil type, in my opinion is engine tuning and jetting, but right behind that is are several other very key parameters. Engine size, rpm, temperature, load.....just to name a few.

Proper "Jetting" (and tuning)

Forget about fuel/oil mix for a second. Think about an old fashioned carburettor and setting air:fuel mixture. This needs to be dialed in just right. It's the point about midway between 14 and 16 to 1 that is the point to get the most energy. 14.7 to 1 (air:fuel) is ideal for normal gasoline engines, called stoichiometric . Lean of stoichiometric can be hot (and damaging and lacking power, of course super lean won't fire and that might be cool), too rich of stoichiometric is cold (and wet rich and lacking power). Stoichiometric is energetic!

A wild example of why I think this is so important. If you are running a 50:1(fuel/oil) ratio and the bike is close to being lean air:fuel jetted, simply going to more oil, like a 20:1 (fuel/oil) ratio, will probably result in a leaned out holed piston.
But, what the heck - why? I put MORE oil in - you may ask...well, even though you added more oil, you have effectively robbed some of the volume used for fuel and air. You have leaned the bike out even further by adding more oil! If the bike has been jetted up correctly for use with a 50:1 fuel/oil ratio, going to a 20:1 ratio could leave the bike dangerously close to piston meltdown, as lean conditions run extremely hot.

Contrary to popular belief very little oil reaches the combustion chamber, IF the engine is metering the fuel mix - properly metering of the fuel mixture must be so that most of the oil falls out of suspension. This condensed oil then migrates to lubricate the friction surfaces of the crank bearings, as well as some of it being pulled into combustion chamber for lubricating and sealing the rings.

Some bikes do carry a very oil rich and a fuel rich mixture recommendation, and I suspect it to be a protective thing as mentioned earlier. The engine manufacturer knows that the correct ratio is dependent on engine and use specifics, and that proper metering of the air/fuel/oil mixture is dependent on many variables such as quality of fuel, air temperature, relative humidity, and elevation, etc. The engine manufacturer simply cannot provide a catch-all metering scenario, as his equipment is sold to areas with a wide array of conditions. The jetting chosen for a factory bike is basically an arbitrary median average. It may be fuel rich for one condition, and fuel lean for another.

Many will want to add less oil to their 2 cycle engine when they see a dark, oily spooge coming from the tailpipe. It would seem logical that if there is oil coming from the tailpipe, that the mixture is carrying too much oil. I for one have used this as a guide when too lazy to pull the spark plug to at least check, or recommending an oil to someone who knows engines.

But that is again where conventional wisdom separates from facts. When an engine is producing this oily residue, it can be due to the air:fuel mixture not being metered properly by the carb, and as a result much of the fuel components get past complete combustion, and turns itself into an oily looking substance along with a small amount of the oil that didn't fall out of suspension prior to combustion.
Adding less oil will not always fix the spooging problem, but rather enhance it, since you have now added more fuel to the mix...and the metering devices (jets, needle, etc) are already allowing too much fuel into the chamber to begin with. The result is even more oily fuel spooge, and the engine a bit less powerful.

A properly set up engine, that is metering the fuel/oil/air mixture to optimum, will see most of the oil fall out of suspension prior to the combustion chamber. If the remaining fuel:air mixture results in about a 14.7:1 air:fuel ratio, then the resulting burn will be clean and powerful - energetic. But may be too hot still for long full throttle conditions. The goal of the tuner is to find these settings and keep then there. It's a moving target, so the exacting tuner has to be very sharp about these things, and know exactly what effects the changes make. This is why just playing with the fuel/oil ratio can be a bit deeper than first blush.

So how to best dial in air:fuel ratio? It depends - most engine manuals supply the basics. Some of the power mechanics here can probably help with your engine. I can't even pretend that I know many of your engines and carbs. My first advice is to contact someone that knows how. Learn where the main jet is, the air screw, the idle screw. Just as important, learn how to "read" the spark plug. Again there are pictures on the web of overly lean, overly rich and perfect mixture spark plugs. If it is white/glazed and looks new after a ride, you may be too lean, black/brown wet is too rich and very light deposits that are light chocolate brown (depending on fuel, fuel additives and oil brand) is about perfect.

Other factors, in general:

All these can effect your fuel/oil decision. BUT mind your air:fuel ratio.

Time at temperature (think wide open throttle for a few seconds vs. 30+ minutes)

Elevation also effects air:fuel ratio and can therefor effect fuel/oil mix ratios.

Temperature and climate (cooler temps and cool moist climate may need less oil)

Smaller engines need more oil - the old days used to be something like 20:1 for small engines, 32:1 for larger engines.

Higher RPM engines need more oil, simply put more piston movement per time period uses more lubrication. This one is sometime overblown or is simply the same as "time at temperature".

More oil for more load. Thing of a 250 lb guy on a 50 cc bike.....everything in balance....

New engine break-in ratios - some engine manufacturers ask for a much more oil rich mixture for engine break in. This can be a topic by itself. I can see some reasons for this, but more is not better.


Fresh mix - to the racers who have all the above dialed in, there is nothing more important than fresh gasoline freshly mixed with 2 cycle oil.

Tank and fuel line cleanliness - you would be amazed what people have found in their fuel tanks, and how fast some lousy fuel lines deteriorate on the inside.

Air Filtration - when your engine seizes up or your engine has some interesting wear problems - yet your plug looks OK, how fast are we still blaming the oil? This may not be a huge of a problem in a clean suburban environment, but plenty of bikes have less than optimal air filtration, which will mess with your carburettor and your engine.

Mixing - silly as it sounds, some folks don't do a great job of mixing their oil and fuel perfectly. People have their own techniques, but I always put some fuel (1/4-1/3 of total) in my (approved) container, add the correct amount of 2-stroke oil and mix well (put lid(s)) on and shake. Then add the remaining fuel and mix well again.

Storage and rust - not to get off track too far but many 2-stroke race oils don't contain anti-oxidants and and rust preventatives. Storing a bike over the winter with this fuel in the tank probably isn't the best anyway, plus there will be very little internal engine protection. Keep this in mind when selecting an oil, and as another aside, with a plastic fuel tank it's best to store it dry anyway.

Oil "helping" with power - a good oil at the right ratio in a perfectly tuned engine for the conditions can help with power, not only getting the most out of the normal pump gasoline, but also not robbing power (and causing excessive wear) with lack of lubrication.

2 strokes can be a headache, but one I willingly trade for output vs. size and weight!
Last edited by a moderator:
Thanks Pablo. Unfortunately for me, while that was rich in chewy information, I got almost no knowledge out of it. :D

I have a Kings "80" chinese happy time type motor. It came with no manual or manufacturer recommendations and a carburator with one main jet and no adjustments but moving the circle clip on the needle. After reading a few sites online, I broke the motor in on 20:1 for one gallon and went to 25:1 for one gallon. After the break in, I removed the head and found that my piston crown was smoothly coated with carbon. I went to 32:1 (which I had been led to believe was correct. I noticed a loss of power at high RPMs and backed back down to 25:1 ever since. My plug stays pretty blackened but the engine runs fairly well.

Perhaps you can give a simple recipe for the neophyte to determine if the motor is drastically over/under oiled. I realize that that is probably an annoying request but while I'm not that bright, I can follow a cookbook.
....... I removed the head and found that my piston crown was smoothly coated with carbon. I went to 32:1 (which I had been led to believe was correct. I noticed a loss of power at high RPMs and backed back down to 25:1 ever since. My plug stays pretty blackened but the engine runs fairly well.

First I need to ask what brand of oil are you using? A thin coating of black could be close to normal, but also could be fuel rich. Sounds like your 32:1 drove you more fuel rich. To be honest, with a top line oil in a simple engine, the difference between 25:1 and 32:1 shouldn't be huge. But if you are running fuel rich, then cut back on oil and lose power at the top end.....this could be a sign that your high rpm jetting is not correct. Only one main jet, but no other adjustments.......so there is plenty of power just off idle with 32:1? Do you ride it wide open throttle a lot or just midline RPM or bog it? Any moistness at the exhaust port?

Perhaps you can give a simple recipe for the neophyte to determine if the motor is drastically over/under oiled. I realize that that is probably an annoying request but while I'm not that bright, I can follow a cookbook.

Certainly not annoying. Man I wish I could just have a cookbook. If you want to stay with 25:1 or 32:1, keep pursuing the knowledge to jet it correctly. Sounds like you are on the right path.
Wow...lotsa good info here....fwiw I have never actually calculated what ratio I use in my Dax 70....I have been using an oil available at Lowes (hardware store) called Pro Mix....Says it's goof for all mix ratios from 16 to 1 to 50 to 1.....So far have been using this stuff for all my lawn tools (professional lawn care / landscaping since 1994) and in my Dax since new....I have been thinking about castor oil since joining this site tho because I hear it is good stuff and since I like to mod for even more power the extra protection couldn't hurt I guess...
First I need to ask what brand of oil are you using? ...

I using the same Walmart oil that I've been using in my chain saws. Probably not the best. I roll the throttle to wide open as I accelerate (I don't snap it open but I do get there fairly quickly) until I get to cruising speed and then vary the throttle position constantly to maintain it within a comfortable range. That's just a habit that I've had since I rode motorcycles. I live at sea level so I tried moving to the 3rd slot (richer) on the needle but I didn't see an improvement and moved it back to the 2nd slot.

I'm the only HT bike in town and this is my first motor so I have no basis for comparison. I may be running as well as these little toys run. I'm just hoping not to destroy it before its time, lugging my 200+ pounds around.
I tried moving to the 3rd slot (richer) on the needle but I didn't see an improvement and moved it back to the 2nd slot.

Now there's a clue, you went richer in fuel and it didn't improve.....if you want to mess with 32:1, get a top name brand oil, top tier gasoline, mix up a fresh batch and try your current setting, then try the first slot (leaner) and see what happens at WOT. If it still has power loss at WOT, just go back to the 2nd slot , (and add the necessary oil, if you want to bring it back to 25:1)

I don't know much about Walmart 2-stroke oil, probably just blended by Warren or contract blended, low end, low cost and labeled for WalMart from one of the big players.
I used to run that cheap hardware store oil in my engine. i wasnt too satisfied at the time with the performance of it but it was there and it worked. we used to run bel-ray racing oil in our dirtbikes, until recently we switched to maxima 927 racing oil. i bought a bottle for my motorbike, i ran a gallon through it and i realised a major difference in performance, better power increase. not so much goopy oil/carbon build up at the exhaust manifold. it costs almost 10 dollors for a small 1QT bottle. expensive but worth it. yet this oil isnt as convenient as hardware store oil, i buy it at our nearest motorsports dealership. others might be out of range of a dealership. maybe this oil is expensive and not as easy to get, but it is worth it when your running it through your engine.
Thanks for your thoughts. I see from your website that there is an Amsoil dealer near where I work. I'll go by there and see what they have and try 32:1 again.

I would never have thought that less oil would rich up the mixture, or that more oil would lean it out.

Again, thanks for the info and I'm happy that you have joined this group.
Last edited by a moderator:
bought new

for the first 325km used organic 2 stock with z max 20-1
then whent to amsoil {synthetic} with z max 32 to 1
at the same time whent to second notch on carb
i got 1 those bore a scopes on ebay for $7.00{a led light at the tip of a flexable wire with magnet and laser pionter}a great tool to look into the cylinder with the plug off and other tite places.anyway the top of my piston is always tan {did see some ware, scraches on the cylinder}same with the plug.it,s for looking in gun bores.

Last edited by a moderator:
Links to eBay may include affiliate code. If you click on an eBay link and make a purchase, this forum may earn a small commission.