2 stroke mixture torture test(outcome suprised me!!)

Discussion in '2-Stroke Engines' started by linnix13, Jul 5, 2009.

  1. linnix13

    linnix13 Banned

    so I did a little torture test today to see exactly what these engines would run on, my engine is a zoombicycles.com 80cc HT. so I usually run 20:1. I mixed up some 15:1 to see how the bike would run, and as it turns out the bike actually ran smoother and had more high end power than on 20:1! it was a tiny bit sluggish in the low rpms though, and there was a barely visible smoke cloud, so then I went to 10:1 again it seemed ok except for the largely evident smoke cloud and it was becoming noticeably sluggish in the low rpms, so I thought to myself "wow I'm just guna go all or nothing on this next mix" so I made up some 3:1!!!!! it was a thick dark blue sludge I didn't think would even be able to flow through the petcock, well after pedaling a block I finally came to a large hill, I coasted down the hill and popped the clutch, to my surprise the engine sprang to life!, it rode at 35+kph just as normal as it rode with the 20:1. Except a huge blue cloud that spewed out the back and a spray of oil. the second I let off the gas the engine started popping and misfiring really bad, it had no power under 20kph but along as I kept it revved up I could pedal to 20 then let of the clutch and ride, I rode for about 10 minutes and brought it home, I tried to keep it running but the second I get of the throttle it bogged down and took about 20 seconds to reach high rpms again, so I'm hugely surprised it actually ran(albeit poorly) on 3:1!!!! I wouldn't recommend this though as it's highly impractical and now I need to go clean the carb and exhaust and the tank thoroughly before I can ride again,
    Last edited by a moderator: Dec 15, 2015

  2. Just_Gasit

    Just_Gasit Member

    Your engine ran better when you went to 15:1 because you leaned the FUEL mixture. You engine may be running slightly rich in the air/fuel mixture when your mixed at 20:1 I'll try to explain, as you add oil to the fuel, there is less fuel and more oil being drawn into the combustion chamber. This is actually LEANING your air/fuel ratio. The more oil, the less fuel for the same amount of air. Now, adding more oil to your mixture is often called by mistake a "rich" mixture but it's only "rich" in oil to fuel ratio. Changing your oil mix ratio usually requires changing your jetting settings to see just how performance is changed. An example of change would be going with a quality 2 stroke motorcycle oil such as Golden Spectrol and mixing 50:1, you would now have more fuel being burned and you would need to lower the needle (raise the clip) to lean the air/fuel ratio. I don't think I would run one of these motors at 50:1 but I may try a quality oil at 32:1 after I break mine in.

    A real torture test would be trying higher ratios like 40 or 50:1 (Use quality oil that has these ratios printed in their specs) and see if your motor stays alive. Of course, it could cause damage, I don't really recommend anyone try this. Your test would only foul plugs and gum up the exhaust, but if run with way too much oil for extended periods, you would be running the engine air/fuel lean and that can cause pinging and too much heat. This could also damage the engine over time.
    Last edited: Jul 5, 2009
  3. linnix13

    linnix13 Banned

    yeah it was pinging bad, well i leaned it back to 20:1(Well maybe even 18:1 i always add a tiny bit more oil to my 20:1 mixture for good measure) and i went for a ride, it was smoky and stalled alot to begin with but after 10 minutes it got better, i have riden for about an hour on the fresh gas and i still have no low end power and it strugles on the hills by going into these mini misfire fits, but i also am runing a ngk b6hs as apose to the chinese one ive ran for the last 3500km, i think im goin to go put that old chinese plug back in after i give it a bath in gas and clean it out, i did this before and the ngk plugs make my motor run like ****, why does the 3500km old chinese plug still out perform the new plugs?
  4. Happy Valley

    Happy Valley Active Member

    Just Gasit, good post.
    Nice to see the fundamentals of pre-mix understood and posted once in a while to keep it current.
  5. RMWdave

    RMWdave Member

    lol more oil sounds great in theroy, but its only helping if you dont try and make it burn good. im going to break mine in at 400ml to 5000ml (can someone put that into a ratio for me)
  6. linnix13

    linnix13 Banned

    sure! thats 12.5:1 and thats sounds good for a break in, i broke mine in around there too.
  7. RMWdave

    RMWdave Member

    awesome i figured it was around there. great!
  8. Scotchmo

    Scotchmo Member

    As Just Gasit stated, your bike appeared to run better since the mixture was affectively leaner, though maybe for a different reason than was stated. True, the more oil, the less gas, but oil is also a fuel. I’m guessing that the real reason was the following; Oil has a much higher viscosity than gasoline. The increased viscosity of the mixture was making it hard for the engine to pull the liquid up through the main jet. The result was less total mixture volume flowing for a given air flow. The same affect as reducing the main jet size.

    Even though oil can burn as a fuel, it does not burn the same as gasoline and the high percentage of oil in the mixture probably fouled your plug. It also can lower the octane.

    I used 16:1 for my first gallon, 24:1 for the second, am running 32:1 now and plan on staying at that ratio.
  9. Mountainman

    Mountainman Active Member

    at least you were experimenting to the rich side
    and not to the extra lean side

    read about the rich is truly not rich and all that stuff
    doesn't fit in with old school !!

    careful with your THING !!
  10. robin bird

    robin bird Member

    Try on a old engine how lean you can go ?? 50 or 60 to one ??
  11. Pablo

    Pablo Motored Bikes Sponsor

    AGAIN. It depends on the oil. HT engine can run all day on SABER at 50:1. Probably would do fine at 80:1. This probably wouldn't be the wisest thing with some other oils. Yet SABER at 20:1 would be just too much oil. It might run, but it would be pointless, well other than as an experiment.
  12. pdxrhett

    pdxrhett Member

    My question is this: Why on 2 stroke dirt bikes people run at 50:1, but with these motors everyone says 30:1 is the way to go? I'm not complaining, but I try to remain environmentally friendly, and using more oil = more fossil fuels...
  13. Pablo

    Pablo Motored Bikes Sponsor

    Because they are using an oil that will work fine at 50:1. Not all oils are the same.
  14. RMWdave

    RMWdave Member

    again people, its preferance.
    there is no perfect mixture when it comes to a 2 stroke, but ideally 32:1 is what most people use in small engine powersports.
  15. bughuggger

    bughuggger New Member

    use gunk not gasoline to clean it. Works perfect.
  16. Fabian

    Fabian Well-Known Member

    I've got some basic knowledge of 2-stroke engines and my understanding through research and empirical knowledge is:

    Oil reduces octane rating: fuel is formulated to a specification that gives the required octane number - adding non volitiles reduces octane so run the highest octane pump fuel. The more oil you add to the fuel, the higher the octane rating you require to compensate for the octane reducing effect of the oil.

    Octane rating: The octane rating is the measurement of the fuels resistance to detonation. The higher the octane rating the slower the rate of burn but the cylinder pressure is more even and consistant throughout the power stroke.
    Higher octane fuels generate more low and midrange torque and allow more spark advance and greater cylinder pressure without detonation - perfect for making more power and torque at a lower rpm - exactly what we need with our Chinese engines.

    Oil and Fuel Ratio and it's effect on power: The more oil added to fuel of a specific octane rating, the more the octane level is reduced. This requires a higher octane rating to compensate.
    The more oil is added the greater the contained cylinder pressure becomes because oil quantity in a poorly manufactured 2-stroke engine (like our Chinese engine kits) is used to create a fluid seal (hydro dynamic seal) between the rings and the cylinder bore - THIS IS A VERY IMPORTANT POINT TO UNDERSTAND.
    With these Chinese engines the best balance between oil and fuel quantity and fuel octane and power is 20:1
    Running above 20:1 may make more theoretical power but it doesn't because the hydro dynamic seal is reduced and the greater the effect of blowby past the piston rings, contaminating the fresh cylinder charge underneath the piston.

    Heat extraction: excess heat through various hot spots on the engine are kept under control through the process of oil absorbing heat and preventing excessive distrotion of the metalic parts.
    Running abouve 20:1, eg, 25:1, 30:1, 40:1 will lead to piston skirt scuffing and evential engine piston siezure if used at wide open throttle for long periods of time even with normal rpm levels - i could go into the bennefits of castor oil, but that's another topic.

    The needle roller bearings are very tollerant of low oil levels - what destroys needle roller bearings in 2-stroke engines is excessive rpm and flat spotting the needle rollers which then vibrate the daylights of the retainer cage and subsequently fall out of the cage, destroying the engine.
  17. Scotchmo

    Scotchmo Member

    I agree that 20:1 gives better lubrication than say 32:1 or 50:1. I still run 32:1 as a compromise. I'll accept slightly reduced engine life for some of the benefits of running less oil including, less chance of plug fouling, less carbon buildup, and less oily mess exiting the exhaust. And as you said, I can use a lower octane fuel. I save a little money on oil and on fuel.

    I usually cruise at 25mph and about 3/4 throttle. I often run full throttle for 20-30 minutes at a time but only when fighting a headwind so my speed is still only 20-25mph. Full throttle runs at speeds above 30mph with a tailwind are restricted to a mile or less. So I can get by with the 32:1 fuel/oil mixture.

    You make good points and there is only one that I don't agree completely with. You should include the following caveat; unless your engine is experiencing pinging or detonation, the higher octane fuel will not improve your low end or mid range torque.
    Last edited by a moderator: Dec 15, 2015
  18. tacoshell4

    tacoshell4 Member

    I run saber at work for all of the handheld equip. at 70:1 never had an issue. any 2 stroke i've ever owned dirtbike and my nsr 50 I run 50:1 never had a lube issue ever I run maxima super m in my bikes
  19. linnix13

    linnix13 Banned

    well im not sure, i just wouldnt feel right running an engine designed for 20:1 on 80:1 regardless of what kind of oil,
  20. GearNut

    GearNut Active Member

    Waaay back when I was a wee little lad, the oil to gas thing was described to me this way. I understood it quite easily.
    Gas is thin and light weight. 2-stroke oil is thick and heavy. Fuel is a mixture of the two.
    Now consider where the carburetor stores the fuel, ready to burn.
    Underneath it, right!
    In order to get the fuel into the engine the carburetor has to suck it straight up a very small tube.
    The more oil you add to the gas, the heavier the fuel weighs.
    The carburetor has to work that much harder to give the engine the fuel it needs. Too much oil and the carburetor will fail it's mission: to give the engine the exact amount of fuel needed. The engine will starve for fuel, get waaaay too much air and get killed. It will burn up from the inside out!
    Now, sip some of this soda through the straw. It's easy to sip ain't it?
    Now sip some of your chocolate milk shake through the straw . It's much harder right?
    Now just think of that fuel mixture.
    Imagine your body is an engine . Imagine your mouth is a carburetor, that straw is the fuel jet and the drink is the fuel.
    Get it?
    Last edited: Sep 24, 2009