Ok, guess the guys at the shop told me wrong when I bought 2 new 2 stroke yz's last week at what ratio to mix my fuel at...they said to mix it at 32:1 so I did... and my son's is puking oil and now they are saying to mix it at 40:1...ok fine but now I have 5 gallons of 32:1 so for you math guys how much fuel do I add to the 32:1 to make it 40:1 ? I am fouling plugs here :) thanks for any help Jeff.
Mix ratio?
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jmics19067
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going from 32 - 1 to 40 -1 will make your bike more prone to plug fouling and spooge.
Not sure that I understand that.jmics19067 said:
Sodflyer I used to say mix everything at 40:1 but I have come to see that small bores, 125cc and less, benefit from a richer oil mix. Were I you I would stick with the 32:1 for the 85 and jet accordingly, or until you aren't fouling plugs anymore. 40:1 would be fine for the 250 but if you don't want to keep seperate fuels for the bikes then jet the 250 accordingly to run on 32:1. IMO a little extra oil isn't going to hurt anything at all as long as you can get it jetted to stop fouling plugs. The 250 might have a little trouble with spooge at 32:1 if you aren't riding wfo a lot but as long as spooge is minimal and you aren't fouling plugs I'd call it good.
Here is some info to help you understand.
Here is some info that will help you understand.
Fuel and Oil Mixture Ratios
When we talk about the "fuel" in the air-fuel mixture for a two-stroke engine, we are really talking about a mixture of fuel and oil. If you richen the pre-mix ratio (20:1 as opposed to 30:1) there is more oil and less fuel in the same volume of liquid, which effectively leans the air-fuel ratio. And this fact gives the clever tuner one more tool to use when the correct jet is not available or when none of the standard jets are exactly right. You can richen the jetting by slightly reducing the pre-mix ratio (less oil). You can lean the jetting by increasing the pre-mix ratio (more oil). The best part is that changes in the pre-mix ratio affect the jetting over the entire throttle-opening range, but the changes in ratio must be small to prevent excess wear from lack of lubricating oil or fouled plugs from too much oil.
DanAKAL said:
Here is some info that will help you understand.
Fuel and Oil Mixture Ratios
When we talk about the "fuel" in the air-fuel mixture for a two-stroke engine, we are really talking about a mixture of fuel and oil. If you richen the pre-mix ratio (20:1 as opposed to 30:1) there is more oil and less fuel in the same volume of liquid, which effectively leans the air-fuel ratio. And this fact gives the clever tuner one more tool to use when the correct jet is not available or when none of the standard jets are exactly right. You can richen the jetting by slightly reducing the pre-mix ratio (less oil). You can lean the jetting by increasing the pre-mix ratio (more oil). The best part is that changes in the pre-mix ratio affect the jetting over the entire throttle-opening range, but the changes in ratio must be small to prevent excess wear from lack of lubricating oil or fouled plugs from too much oil.
jmics19067
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this is what I would belive to be correct. although I may not be 100 % accurate in the scientific explanation of things the general blanket statements would be true as well as the idea behind it.
spooge is incomplete burning of the gas/oil mixture and spark plug fouling is caused by the tip of the plug not being hot enough to burn off any deposits left over from the combustion process.
the gas/oil mix in your tank is an apple, the air/fuel mixture in your combustion chamber is an orange both are needed to make the fruit salad appetizing but they are different.
you need the proper air/fuel ratio to burn all of the fuel and consume all of the air at the right time to make the best controlled heat which is the source of power that pushes the piston down. Too much fuel and the tempature drops, losing power and leaving unburnt fuel.Ever burn leaves in the fall? You have a small fire and you throw a large pile of leaves on the small fire you choke off the air and all you have is smoke until the air flow can can catch up to the fuel(leaves)trying to burning.
Too little fuel and the tempatures go up uncontrollably ,think of a cutting torch when you hit the oxygen lever.
In your gas/ oil mixture the gas is the fuel in the fuel air mixture.The gas is readily burned when mixed with air and the oil will burn when the tempatures get hot enough for it to flash.32-1 is 32 parts gas to 1 part oil 40 -1 is 40 parts gas to 1 part oil. so for every measured drop that goes thru your carb the 40 -1 will have more gas in it than the 32 - 1.That could easily aggravate the problem of too low of combustion tempatures resulting in more unburnt spooge and fouled plugs. Where if you adjust the carburator so less fuel goes in the combustion chamber for a given amount of air where all of the fuel is consumed tempatures go up consuming the oil and keeping the plug tip burned clean.
so you want enough oil to protect the engine then the right fuel air mixture to burn everything clean in a safe, controlled, consuming all ingredients, burn.
does that make sense a heck of a lot easier for me to visualize it than to type it
spooge is incomplete burning of the gas/oil mixture and spark plug fouling is caused by the tip of the plug not being hot enough to burn off any deposits left over from the combustion process.
the gas/oil mix in your tank is an apple, the air/fuel mixture in your combustion chamber is an orange both are needed to make the fruit salad appetizing but they are different.
you need the proper air/fuel ratio to burn all of the fuel and consume all of the air at the right time to make the best controlled heat which is the source of power that pushes the piston down. Too much fuel and the tempature drops, losing power and leaving unburnt fuel.Ever burn leaves in the fall? You have a small fire and you throw a large pile of leaves on the small fire you choke off the air and all you have is smoke until the air flow can can catch up to the fuel(leaves)trying to burning.
Too little fuel and the tempatures go up uncontrollably ,think of a cutting torch when you hit the oxygen lever.
In your gas/ oil mixture the gas is the fuel in the fuel air mixture.The gas is readily burned when mixed with air and the oil will burn when the tempatures get hot enough for it to flash.32-1 is 32 parts gas to 1 part oil 40 -1 is 40 parts gas to 1 part oil. so for every measured drop that goes thru your carb the 40 -1 will have more gas in it than the 32 - 1.That could easily aggravate the problem of too low of combustion tempatures resulting in more unburnt spooge and fouled plugs. Where if you adjust the carburator so less fuel goes in the combustion chamber for a given amount of air where all of the fuel is consumed tempatures go up consuming the oil and keeping the plug tip burned clean.
so you want enough oil to protect the engine then the right fuel air mixture to burn everything clean in a safe, controlled, consuming all ingredients, burn.
does that make sense a heck of a lot easier for me to visualize it than to type it
I think we are all saying the same thing and I understand how increasing fuel can cause plug fouling. Giving it a stretch I can understand how it could possibly increase spooge. However, with all things remaining the same (carb jets, slides, etc) I have never witnessed decreasing the amount of oil in the fuel would cause plug fouling or spooge. I would think that to achieve this there would have to be a signifiant decrease. Something from like 32:1 to 60:1. I have not seen this from 32:1 to 40:1 without increasing jet size. I would be very interested to hear about this if any of you have experienced it. May be like my 40:1 thoughts. It always seemed to work well until a year or so ago when I went from 32:1 to 25:1 and increased the main and pilot jets on some small bore bikes. I must admit that spooge showed up slightly but the bike performed better and the top end looked better after doing this.
OH the balancing act we call jetting!!!!!!! Sometimes I think a trip to the dentist is more fun!!!!!
OH the balancing act we call jetting!!!!!!! Sometimes I think a trip to the dentist is more fun!!!!!
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Great info here guys.... it's been 10-12 years or so but I am picking it back up agan. lastnight I went ahead and rejetted the 85's carb down from the stock jets 38?( both of them) pilot and main to the ones that came with the new bike 36-35? somewhere around there so I will see this weekend if it calms the spooge down a bit. The shop said to mix at 40:1 then see if it's still the same and if so rejet to a 30 main... this seems to be quite a bit of a jump here....right? I will keep the 32:1 easy enough, plus I feel better about more oil in the mix :) Thanks for the info again! Jeff.
MX-727
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That last bit of info is the problem. You will need to lean the bikes out quite a bit to compensate for the lower air density at your altitude.
The easiest thing to do, is to set aside a riding day and commit yourself to concentrating on nothing but jetting the bikes. If you don't, you tend to nibble away at it for several weeks and end up having several less than enjoyable rides. Do it in one shot and get it behind you, until the weather changes or you start changing pipes, reedblocks, etc.. :)
The easiest thing to do, is to set aside a riding day and commit yourself to concentrating on nothing but jetting the bikes. If you don't, you tend to nibble away at it for several weeks and end up having several less than enjoyable rides. Do it in one shot and get it behind you, until the weather changes or you start changing pipes, reedblocks, etc.. :)
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I picked up some smaller jets for the bikes yesterday, I started on the 85 by swapping the 35 main to the 30 and the pilot as well than placing the needle clip from the 2nd down to the 3rd down and gave it a buzz around the block...... was not happy with it at all...flat bottom end and so-so top. I changed it back to the 35 and the pilot as well....took it out again...better this time but not what I wanted so this time I put the clip on the first setting on the top... I can say it's running great now :) but I don't have any time on this setting really yet so I wanted to say thanks again for helping me go in the right direction with this issue. Jeff.
