Part Throttle Operation Of A Chainsaw

[Vintage Engine Repairs]

I have seen a number of posts where people have said they have been babying their saw using only part throttle for the first few tanks. When we get something new, we want to take care of it, don’t want to over work it etc.

The reality is, full throttle under load is the best way for your saw to run. The carburettors in outdoor power equipment like chainsaws, hedge trimmers, whipper snippers don’t have a part throttle fuel supply that is intended to be used for load. They are either designed to idle or cut at full throttle loaded. If you part throttle a saw you are only getting fuel from the idle and progressive idle drillings. The progressive idle drillings are only there to allow the engine to transition from idle to full throttle, not to cut with. Doing so can lead to less than optimal lubrication and can in worst case scenarios cause scuffing, scoring or seizures. Especially when you combine it with a dull chain, low oil ratio, a hot day or you’re leaning on the saw.

I was browsing a Stihl manual for something totally unrelated, but happened across this. Straight from the horses mouth so to speak - second to last possible cause of the lean seizure. Don’t part throttle your saw
I hope someone finds it useful.

 

[Mad Professor]

Warming up the saw is more important. So is so for cars tractors motorcycles........

 

[Vintage Engine Repairs]

Warming up the saw is more important. So is so for cars tractors motorcycles........

Yes absolutely! I was about to see a 660 a while ago when I was on the hunt for one, I asked a guy on marketplace if he could just start it up for me on video. He started it up cold, instantly pinned it a few times and shut it off. I thanked him and passed.

 

[PV Hiker]

Tom thanks for posting this. It is good to note that on M-Tronic saws running on part throttle and light loads the computer will push rich and if it still does not see a load will shut down the saw. If you are doing light loads you need to put it into a log every so often to get a load on it to make the computer happy.

 

[Vintage Engine Repairs]

Tom thanks for posting this. It is good to note that on M-Tronic saws running on part throttle and light loads the computer will push rich and if it still does not see a load will shut down the saw. If you are doing light loads you need to put it into a log every so often to get a load on it to make the computer happy.

Oh wow, I didn’t know that, thanks for sharing.

 

[Del_]

Two strokes also need a lot less lubrication at low throttle settings so I doubt the info stating never run a part throttle setting.

When limbing a log and cutting a one inch diameter limb off of that log I seldom rev a saw to full throttle. Usually I just blip the throttle just before limb contact and let engine and chain momentum do the cutting.

I agree with no partial throttle under heavy loads.

Some two stroke outboard motors have a variable fuel/oil ratio system running as low as 120/1 at low rpm and the only problem I've every heard of with them is a system failure causing damage, and not the lower fuel oil ratio.

I believe some of this no partial throttle operation causing damage to chainsaws is myth when it comes to real light loads like cutting twigs off of limbs and logs.

 

[HumBurner]

Unfortunately, the real world dictates that full throttle is not always possible or safe.


When cutting brush/sprouts, sometimes you're blipping the throttle to make a 1 second or less cut, or you need to nip in and out to avoid catching objects or debris. Other reasons.

One other reason for safety is when tickling the last few fibers of a cut. Even gunning for a split second or less may not reach WOT, but any more could be putting the bar/saw/operator at danger.


Optimum saw running conditions can't be priority 100% of the time.

 

[PV Hiker]

Tom your example image from Stihl might be part throttle use for extended time, example like milling. Most people milling at part throttle are most likely tuning their saws to compensate for being a little lean. To get a piston damage like shown one would possible be at half pressed throttle and cutting light loads and bucking for extended amount time at running lean. As mentioned it's fine to limb blipping and light load limbing as it is a short duration in time for most users.

 

[link]

I have seen a number of posts where people have said they have been babying their saw using only part throttle for the first few tanks. When we get something new, we want to take care of it, don’t want to over work it etc.

The reality is, full throttle under load is the best way for your saw to run. The carburettors in outdoor power equipment like chainsaws, hedge trimmers, whipper snippers don’t have a part throttle fuel supply that is intended to be used for load. They are either designed to idle or cut at full throttle loaded. If you part throttle a saw you are only getting fuel from the idle and progressive idle drillings. The progressive idle drillings are only there to allow the engine to transition from idle to full throttle, not to cut with. Doing so can lead to less than optimal lubrication and can in worst case scenarios cause scuffing, scoring or seizures. Especially when you combine it with a dull chain, low oil ratio, a hot day or you’re leaning on the saw.

I was browsing a Stihl manual for something totally unrelated, but happened across this. Straight from the horses mouth so to speak - second to last possible cause of the lean seizure. Don’t part throttle your saw
I hope someone finds it useful.


View attachment 1018549

The manual for my 4 cylinder 1000cc 50hp Yamaha engine say; let the engine run for 5 minutes at idle before you put it in gear - else it will diminish life expectancy.

 

[HansFranz]

...hedge trimmers...,

The manual for my (Poulan) hedge trimmer says to open the throttle only enough to cut what you're cutting.

Quotes:
"It is recommended that the engine not be operated for longer than 30 seconds at full throttle...Use the minimum throttle speed necessary to effectively cut hedges..."

I suspect this is because it has some kind of clutch or rubber baby buggy bumper arrangement that allows the engine to continue running, even if the blades don't reciprocate for the full stroke (for example when you're chewing through a thick branch)...

But yeah: Definitely always run a chainsaw at full throttle when cutting, not just for engine longevity but also for safety (less chance of "grabbing" and resultant kickback when the chain is moving fast...the main reason kickbacks happen is because the chain stops, and that energy goes either into bending the branch into a spring, or throwing the saw backward and up...and there's less chance of the chain stopping if it has a lot of speed and burning gasoline behind it...)

 

[Vintage Engine Repairs]

Two strokes also need a lot less lubrication at low throttle settings so I doubt the info stating never run a part throttle setting.

When limbing a log and cutting a one inch diameter limb off of that log I seldom rev a saw to full throttle. Usually I just blip the throttle just before limb contact and let engine and chain momentum do the cutting.

I agree with no partial throttle under heavy loads.

Some two stroke outboard motors have a variable fuel/oil ratio system running as low as 120/1 at low rpm and the only problem I've every heard of with them is a system failure causing damage, and not the lower fuel oil ratio.

I believe some of this no partial throttle operation causing damage to chainsaws is myth when it comes to real light loads like cutting twigs off of limbs and logs.

Completely agree, no way would light limbing, etc damage a saw. Loading an engine up in heavy loads for extended periods of time is where the issues could start to occur, over a number of tanks.

 

[Vintage Engine Repairs]

Unfortunately, the real world dictates that full throttle is not always possible or safe.


When cutting brush/sprouts, sometimes you're blipping the throttle to make a 1 second or less cut, or you need to nip in and out to avoid catching objects or debris. Other reasons.

One other reason for safety is when tickling the last few fibers of a cut. Even gunning for a split second or less may not reach WOT, but any more could be putting the bar/saw/operator at danger.


Optimum saw running conditions can't be priority 100% of the time.

You’re spot on, there is nothing wrong with part throttle when zipping up small limbs. I think they are referring to continued part throttle for multiple tanks under decent load.

 

[Vintage Engine Repairs]

Tom your example image from Stihl might be part throttle use for extended time, example like milling. Most people milling at part throttle are most likely tuning their saws to compensate for being a little lean. To get a piston damage like shown one would possible be at half pressed throttle and cutting light loads and bucking for extended amount time at running lean. As mentioned it's fine to limb blipping and light load limbing as it is a short duration in time for most users.

Spot on, fully agree mate. I think what they are trying to discourage is people using saws part throttle the whole time especially under heavy load bucking or as you say, milling. I suspect stihl want to reach out to those who think, like when driving a car for example, it’s bad to full throttle it.

 

[Vintage Engine Repairs]

The manual for my (Poulan) hedge trimmer says to open the throttle only enough to cut what you're cutting.

Quotes:
"It is recommended that the engine not be operated for longer than 30 seconds at full throttle...Use the minimum throttle speed necessary to effectively cut hedges..."

I suspect this is because it has some kind of clutch or rubber baby buggy bumper arrangement that allows the engine to continue running, even if the blades don't reciprocate for the full stroke (for example when you're chewing through a thick branch)...

But yeah: Definitely always run a chainsaw at full throttle when cutting, not just for engine longevity but also for safety (less chance of "grabbing" and resultant kickback when the chain is moving fast...the main reason kickbacks happen is because the chain stops, and that energy goes either into bending the branch into a spring, or throwing the saw backward and up...and there's less chance of the chain stopping if it has a lot of speed and burning gasoline behind it...)

Sorry maybe I wasn’t too clear, I used a hedge trimmer as an example of not having a mid circuit for cutting with. Those engines are already quite loaded by the attachment and any extra load trimming brush is very light, so they generally aren’t going to have any issues cutting at less than full throttle, other than carbon fouling. It’s more about heavy continued load like a 2 stroke would see bucking large rounds etc.

 

[Captain Bruce]

I have seen a number of posts where people have said they have been babying their saw using only part throttle for the first few tanks. When we get something new, we want to take care of it, don’t want to over work it etc.

The reality is, full throttle under load is the best way for your saw to run. The carburettors in outdoor power equipment like chainsaws, hedge trimmers, whipper snippers don’t have a part throttle fuel supply that is intended to be used for load. They are either designed to idle or cut at full throttle loaded. If you part throttle a saw you are only getting fuel from the idle and progressive idle drillings. The progressive idle drillings are only there to allow the engine to transition from idle to full throttle, not to cut with. Doing so can lead to less than optimal lubrication and can in worst case scenarios cause scuffing, scoring or seizures. Especially when you combine it with a dull chain, low oil ratio, a hot day or you’re leaning on the saw.

I was browsing a Stihl manual for something totally unrelated, but happened across this. Straight from the horses mouth so to speak - second to last possible cause of the lean seizure. Don’t part throttle your saw
I hope someone finds it useful.


View attachment 1018549

Chainsaws are like jet-ski's........you don't idle around the ramp, you point at open water, and go WOT.

 

[KASH]

My saws see lots of sustained part throttle operation with no damage.Examples winches water pumps brush saws I have never saw these run at full throttle.The old snow mobiles with Tilly carbs spent 90 percent of their operating time at midrange most of the ones that cooked were due to lean operation at full speed.
When I was around 13 years old I mounted a Pioneer RA on a balloon tire bike it spent most of its time at midrange we ran the bicycle for a at least 5 years.
I believe that at midrange both high and low speed cicuits are feeding the motor.
Here one for thought outboards and snow machines with VRO oiling it might be 160 to 1 at idle but at full speed it is likely to be around 20to1.
Here is what I do not understand if the engine is not getting enough oil at mid range but it gets the portion of the gas but no oil then should not the fuel line and gas tank start to fill up with the excess oil that supposedly can not get to the engine because it is mid way between the high and low circuits.
Kash

 

[HansFranz]

Here is what I do not understand if the engine is not getting enough oil at mid range but it gets the portion of the gas but no oil then should not the fuel line and gas tank start to fill up with the excess oil that supposedly can not get to the engine because it is mid way between the high and low circuits.

The oil-injected outboards that I've owned (Yamaha 3-cyl 40 hp and Evinrude E-Tec 25 hp) used separate gasoline and oil tanks.

I've always put some oil into the gas tank just in case the oil injection system goes belly-up...and years back I heard of some guys just scrapping the oil-injection system altogether and burning straight 2Mix (32-to-1 or 50-to-1 TCW-3) all the time...

 

[Old2stroke]

The oil-injected outboards that I've owned (Yamaha 3-cyl 40 hp and Evinrude E-Tec 25 hp) used separate gasoline and oil tanks.

I've always put some oil into the gas tank just in case the oil injection system goes belly-up...and years back I heard of some guys just scrapping the oil-injection system altogether and burning straight 2Mix (32-to-1 or 50-to-1 TCW-3) all the time...

Yeah, a lot of guys with dirt bikes, especially motocross ones would disable the oil pump and go with premix in the tank for more reliability.

 

[Mad Professor]

The manual for my 4 cylinder 1000cc 50hp Yamaha engine say; let the engine run for 5 minutes at idle before you put it in gear - else it will diminish life expectancy.

Long lost the link, or it's gone now......but the HuskyVarmint people stated 90% of wear occurs in the first 5 minutes of operation. 2-stroke specific

Growing up with farm equipment, I was always taught to run engines until temp gauge starts to move (~ 100-120 oF) or cylinder is warm/hot to the touch, especially in winter. I've still do that with my cars/trucks, and air and water cooled engines.

Now I have 70-80 year old tractors still running fine. When they were made straight 30W oil was used except in sub-freezing temperatures. Oils have come a long way , but why might these old tractors still be running fine?

From an early 1950s manual:

 

[Del_]

Yeah, a lot of guys with dirt bikes, especially motocross ones would disable the oil pump and go with premix in the tank for more reliability.

Some of the irony of blaming the vro system is when only one cylinder goes bad and yet it is blamed on the vro.

It most likely is a lean condition caused by one of the carbs having a problem and running that cylinder lean and it the damage would occur even if the fuel and oil were mixed in the tank and the vro deleted.

OMC's are set up so if the vro system fails then a very rich oil/fuel ration results.

First run of the season or first run of the season on the hose or in a barrel I run a mixed tank to make sure that the vro system is drawing the oil tank down. Usually it is obvious by the amount of smoke seen when ran. VRO is a much maligned system for a lot of very wrong reasons.