Fuel mixture terminology.

[Machold]

The fuel/air mix is a topic that is always thoroughly confusing for me, whether the fuel/oil mix is 40:1 or 50:1 (aka, fuel).

If you "lean out the saw", are you adding fuel or air? If you "richen it up", are you adding fuel or air?

 

[Giles]

I have worked on small engines for over 50 years. I raced motorcycles for a number of years and learned a lot about tuning.
Today's gasoline and oil is quite different then a few years ago, and this has to be considered for optimum tuning.
My gasoline engines are tuned for their use and working conditions.
Correct tuning must be carried out in a "real world" situation----tuned with the engine under load and taking a SPARK PLUG READING.
Any time I get a different chainsaw, I start out by warming the engine to operating temperature, remove spark plug and install a NEW sparkplug, and immediately begin several cuts with the saw under maximum load. Very little idling, just go from one cut to another as quickly as possible.
After several cuts, I remove the sparkplug after shutting off engine during cut.
The spark plug porcelain insulator should have a tan or grey color. A white or slightly colored porcelain, should be corrected by adjusting high speed mixture accordingly. Much better to have a dark colored porcelain if the saw performs as intended.
It will be discovered that different brands of gasoline and oils will give slightly different readings.

 

[Chris-PA]

I have worked on small engines for over 50 years. I raced motorcycles for a number of years and learned a lot about tuning.
Today's gasoline and oil is quite different then a few years ago, and this has to be considered for optimum tuning.
My gasoline engines are tuned for their use and working conditions.
Correct tuning must be carried out in a "real world" situation----tuned with the engine under load and taking a SPARK PLUG READING.
Any time I get a different chainsaw, I start out by warming the engine to operating temperature, remove spark plug and install a NEW sparkplug, and immediately begin several cuts with the saw under maximum load. Very little idling, just go from one cut to another as quickly as possible.
After several cuts, I remove the sparkplug after shutting off engine during cut.
The spark plug porcelain insulator should have a tan or grey color. A white or slightly colored porcelain, should be corrected by adjusting high speed mixture accordingly. Much better to have a dark colored porcelain if the saw performs as intended.
It will be discovered that different brands of gasoline and oils will give slightly different readings.

But these all-position carbs are different than the ones on other equipment - does any of your other stuff get so rich it misfires (4-strokes) just by reducing the load a little bit? Reading plugs can be a useful long term check, but there's not really any practical way to run the saw without having it go through that so-rich-it-misfires zone, so your plug will have that on it too - it's cumulative based on all the conditions the plug was exposed to. Would you be able to tell that sometimes it's lean under those circumstances?

 

[Giles]

But these all-position carbs are different than the ones on other equipment - does any of your other stuff get so rich it misfires (4-strokes) just by reducing the load a little bit? Reading plugs can be a useful long term check, but there's not really any practical way to run the saw without having it go through that so-rich-it-misfires zone, so your plug will have that on it too - it's cumulative based on all the conditions the plug was exposed to. Would you be able to tell that sometimes it's lean under those circumstances?

The all-position carburetor is the cause of many engine failures. Kind of like---it works in any position but not right in any. It is not a simple matter to get the carburetor calibrated right---you can't because of the design.
With two stroke motorcycle carburetors, IN GENERAL, the idle was controlled by air mixture screw in relation to an idle jet --idle to app. 1/4 throttle was controlled by the idle mixture in conjunction with the slide throttle cut-away, mid range was controlled by the needle jet in relation to the main jet. There was no High Speed adjustment. That had to be adjusted by position of needle in relation to main jet size. In all the transfer stages of this type carburetor, all systems overlapped.
I stated all this because the all-position carburetor doesn't work a fraction as good and it is so small with tiny fuel metering that the least bit of restriction can cause problems.
I think most people adjust their carburetors by "sound" and RPM while under no load conditions. I DON'T and I have never encountered an engine failure caused by a lean carburetor. I also differ from a lot of other people in that if I have a change in running condition, I clean the carburetor and return the adjustment screws exacthy as they were. Adjusting the carburetor only "maskes" the problem.
We just have to work with what we have untill a better carburetor is offered.
Sure--it's a lot of work to get it close to right but certinally less work then an engine failure!

 

[z71mike]

The fuel/air mix is a topic that is always thoroughly confusing for me, whether the fuel/oil mix is 40:1 or 50:1 (aka, fuel).

If you "lean out the saw", are you adding fuel or air? If you "richen it up", are you adding fuel or air?

When you "lean" a mixture, you're not ADDing anything. In fact, you are removing fuel from the air/fuel mixture. And the amount of air never changes. The center throat in the carb provides consistent throughput (until you bore it out with a grinder).

Let me try to explain this a little clearer, with pictures. I was bored at lunch, so I spent a little while with MS Paint putting this together. I also made a pictorial explaining why a 40:1 premix causes a leaner condition than 50:1.
Disclaimer: I'm a bad artist and I am not a college professor. This is merely a teaching aid drawn-up in 20 minutes. Anyone please correct mistakes if uncovered.
________________________________________________________________________________

________________________________________________________________________________

 

[Machold]

Thanks for the explanation, but your pics didn't show up... almost; they arrived after awhile. Thanks.

Lean = less fuel; rich = more fuel, and in both cases the air is the same.

The 50 vs 40 is also very helpful.

If there is less oil, there is less pollution; more oil is more pollution; BUT, how does the mix affect the working of the saw in each case?

 

[z71mike]

If there is less oil, there is less pollution; more oil is more pollution; BUT, how does the mix affect the working of the saw in each case?

That's a complicated answer, really. Not quite sure how to answer it.

More oil, more lubrication, less fuel in the mix so you need to richen up your carb.

Richer runs cooler and fouls plugs. Leaner runs hotter and smokes engines.

 

[beerbelly]

opcorn:

This is good stuff......

 

[Machold]

If you are burning more oil, surely the effluent is going into the atmosphere, which is why the State of California is banning/has banned (?) the 2 stroke engine.

 

[beerbelly]

If you are burning more oil, surely the effluent is going into the atmosphere, which is why the State of California is banning/has banned (?) the 2 stroke engine.

I started this thread so I feel I have the right to add a somewhat unrelated comment (by the way..this turned into some great conversations. Very informative. Keep it up!)

Anyway....We have to buy saws with epoxied mixture screws and cats. We are not allowed to make any type of emission mods on our vehicles! Yet Hollywood...Hollywood CA the last time I checked, can make movie after movie with huge explosions, car chases with explosions, and we as a country are allowed to race cars every weekend from Feb-Nov. Don't get me wrong..I like racing! But I'd be willing to bet one big movie explosion and 6 months of testing, practice & racing, puts more pollution in the atmosphere than all our chainsaws combined! Guess whe know where the money & influence is!

 

[demc570]

I started this thread so I feel I have the right to add a somewhat unrelated comment (by the way..this turned into some great conversations. Very informative. Keep it up!)

Anyway....We have to buy saws with epoxied mixture screws and cats. We are not allowed to make any type of emission mods on our vehicles! Yet Hollywood...Hollywood CA the last time I checked, can make movie after movie with huge explosions, car chases with explosions, and we as a country are allowed to race cars every weekend from Feb-Nov. Don't get me wrong..I like racing! But I'd be willing to bet one big movie explosion and 6 months of testing, practice & racing, puts more pollution in the atmosphere than all our chainsaws combined! Guess whe know where the money & influence is!

DANG STRAIGHT!! OR ROCKETS OR JETS OR POWER PLANTS-- AND SO ON---GREAT THREAD-THANK YOU:msp_smile:

 

[demc570]

AWSOME INFO! I UNDERSTAND MORE NOW MYSELF:msp_smile: THANKS FOR GOOD INFO,AND POST

 

[z71mike]

AWSOME INFO! I UNDERSTAND MORE NOW MYSELF:msp_smile: THANKS FOR GOOD INFO,AND POST

Glad I could help :msp_biggrin:

 

[SawTroll]

The fuel/air mix is a topic that is always thoroughly confusing for me, whether the fuel/oil mix is 40:1 or 50:1 (aka, fuel).

If you "lean out the saw", are you adding fuel or air? If you "richen it up", are you adding fuel or air?

What can be lean or rich is the fuel to air mix - rich is more fuel to the air, lean is less fuel to the air. The amount of air is controlled by other factors than the settings of the carb, most notably carb venturi, transfer capasity of the cylinder, and the flow of the muffler.

The lean/rich terminology should not be used about the fuel to oil mix, as that may confuse people....

 

[demc570]

What can be lean or rich is the fuel to air mix - rich is more fuel to the air, lean is less fuel to the air. The amount of air is controlled by other factors than the settings of the carb, most notably carb venturi, transfer capasity of the cylinder, and the flow of the muffler.

The lean/rich terminology should not be used about the fuel to oil mix, as that may confuse people....

:msp_smile:

 

[beerbelly]

I'm sure there are a way around that epoxy - or more likely through it...

I've made a decision! Being my saw (5105) is still under warranty, I am going to leave the epoxied screws the way they are. It runs really good in cold/dry weather and in warm/humid. I really like the saw. If Dolmar decided for me that is the way to go, I will go with it. If it goes bad during the warranty, I'll have the dealer fix it. After the warranty... It is mine!