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

linnix13

Member
Local time
1:57 PM
Joined
Mar 6, 2009
Messages
220
Location
dundas ontario
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:
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:
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.

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

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