chopperlot
ArboristSite Lurker
HAVE BEEN USING A HUSKY 395XP FOR MILLING FOR 3.5 YEARS USING A 46" BAR AND MILLING HARDWOOD (IRONBARK) I RUN 25:1 MIX NEVER HAVE A PROB. :greenchainsaw:
oil mix ratio for milling
- Thread starter mikefunaro
- Start date
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Chickaloon
ArboristSite Lurker
I think the argument that the saw is running leaner is accurate if all you care about is gas to air ratio, but when there is oil substituted for gas and it runs through your cylinder, then the lubrication factor is quite high.
You should only have to adjust your carb if you are running LESS than 30:1
So as long as you mix rich with oil and keep your carb setting at the standard 50:1, then you will not be in danger of overheating your saw.
This has become an interesting thread I must say
You should only have to adjust your carb if you are running LESS than 30:1
So as long as you mix rich with oil and keep your carb setting at the standard 50:1, then you will not be in danger of overheating your saw.
This has become an interesting thread I must say
John Bartley
ArboristSite Lurker
Ummm ... not quite true....
It's true that the built up carbon will not score your piston or cylinder as long as it stays where it builds up.
However...
The problem occurs (and I have seen it many times in my years as a saw dealer) when a chunk of built up carbon breaks away and get trapped between the piston and cylinder. The scoring from the trapped carbon can be identified when the scoring happens in a place that wouldn't normally be identified with lean air/fuel mixture failure, and when a pressure/vac test reveals no leaks. Troubleshooting and failure analysis will always tell the true story.
As regards richening the fuel/oil mix for milling, my preference would be to richen the fuel/air mix (not the fuel/oil) so that the saw runs a bit cooler and let the oil work in its correct temperature range.
cheers
John
slabmaster
ArboristSite Guru
+1 I agree on both counts! Carbon is harder than aluminum and can surely damage a piston in a saw fast.As for the fuel, as i said earlier when you richen your oil to the mix, the carb has to also be adjusted for the change as well.Even a 4 stroke will burn up when run lean when it's getting all the oil it can from the oil pump.The extra oil doesn't help the saw when it's getting to little gas to the air mixture no matter how much oil is in the mix.And by adding more oil to the mix,you are feeding less gas to the saww which can cause it to run too lean.I have a motec degree in small engine repair, so it think i know what i'm talking about here.
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And by adding more oil to the mix,you are feeding less gas to the saww which can cause it to run too lean.I have a motec degree in small engine repair, so it think i know what i'm talking about here.
Most small engines designed to last for some time are made with a range of operating tolerances. It's true that if you are operating right on the border of leaness with a saw, a very small additional increase in the amount of air can cause damage but let's assume the saw is operating in the middle of the range so it can tolerate some changes in leaness. The question is how much can it tolerate.
Lets say one day a saw is tuned with the air pressure at 1000 mb and the next day the air pressure increases to 1020 mb. Should the saw be retuned?
1000 to 1020 mb is not a big variation, but it represents 2% change in air pressure. That means the saw will get ~2% more oxygen than when the saw was first tuned.
Changing the mix from 50:1 to 40:1 will result in only a 0.5% difference in air to gas ratio - so the normal change in air pressure will cause a greater variation in leaness than changing the mix from 50:1 to 40:1
Atmospheric pressure at sea level can vary by +/- 2%, from around 990 to 1030 mb, or over a 4% range. To make a 4% "air to gas ratio" the "mix ratio" will have to be changed from 50:1 to 16:1. This air pressure increase is about the same as dropping from 1000 ft above sea level to sea level. Except for a guy that raced saws, I don't know of anyone that successfully operates saws and retunes for this 1000 ft difference.
To provide another indication of when saws should be retuned when dropping from altitude to sea level, lets look at the following, dropping from 2000 ft represents a 7% difference in air pressure, 4000 ft a 13% difference, and 6000 ft a 19% difference. Where I live pretty well all our forests are below 2000 ft and I do not know of any faller that retunes for altitude so it seems than that saws can readily tolerate this 2000 ft or 7% difference. Bear in mind I'm not saying that saws would not benefit from a retune, its just that I don't see fallers doing it and I don't see their saws being damaged. Anyway, the 2000 ft difference is equivalent of a mix ratio change from 50:1 to 11:1.
As others have said, well before then, a more significant problem of dropping the mix ratio will be carbon buildup due to too much oil.
slabmaster
ArboristSite Guru
Air pressure and volume are two different things Bob.The carb has to be readjusted for volume not air pressure, so that's why you don't see the fallers readjust for altitude.When you put more oil in the mix, you're changing the fuel volume not pressure.:monkey: Add ethonal in the mix and you have a real concern today when running lean in a chainsaw.More so when milling!
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Humm . . . . I can see you have not really understood what I have posting. The pressure and volume are indeed confusing. Let's stick to molecules since they are more concrete.
The amount of heat or energy from each firing of the plug depends on the number of molecules of air, and the number of molecules of gas (fuel) inside the cylinder. The number of molecules of gas is more or less fixed by the carby jet but the atmospheric air pressure will affect the number of molecules of air getting inside the cylinder. That is why is a saw tuned for 6000 ft above sea should be retuned when operating at sea level. Otherwise the saw will take in too much air and run too lean. It is even recommended that some saws are re-jetted for large differences in elevation.
The reality is that the variation is ambient air pressure regularly changes the degree of leaness by about 2 % and most saws cope with this quite well. Changing the gas-oil mix from 50:1 to 40:1 changes the number of molecules of gas relative to the number of molecules of air by only about 0.5%
slabmaster
ArboristSite Guru
What i am saying is anytime the air fuel mixture has been changed weather it from altitude or less gas in the mix, the carb should be adjusted for the change as well.I always make sure the saw is running slightly in the rough at high speed after any change in the fuel mixture.I have noticed the rpms change when going from 50/1 to 40/1.so that says something about readjusting the carb when changing the mix.Better to be safe than sorry.
Yep - I can definitely agree with that.
DMax441/241
New Member
More oil = lower octane also which in turn creates more heat
