&$^#$@ Chainsaw Won't Tune

[freudianfloyd]

I bought a Stihl MS211c chainsaw for $20 from a yardsale. The guy said he couldnt get it to run. It looks like it has barely been used.

Anyway, I notice right away the choke linkage has popped out and you couldnt get it choked to start it. 5 minutes later, I had the saw firing up.

It did run, but it obviously needed tuned. I figured I would clean the carb while I was at it and start with new gas.

Fire it back up, and it runs like ****. It idles way too fast, and bogs big time when pulling the trigger.

Now I will admit, I **** at tuning a 2 stroke carb. I just cant hear it right, I get nervous having it running at full speed to set the high side, I just cant seem to master this skill.

But I figure I need to learn, so I invest in a contactless tach. Hook it up and start it again.

I have read to warm the saw up and then set the idle screw all the way in, and then back it out until the chain stops spinning.

Problem 1, turning the idle screw does not speed up or slow down the saw......until it does! Then it drops from 4k or 5k rpm to 2k instantly and dies. Does this no matter what. If I turn the idle screw in even an 1/8th of a turn from where it is at 2k, it jumps back up to 5k. It's like there isnt an inbetween.

So I get it as close to 2700, 2800 rpm and then go to adjust the low speed, again, it doesnt seem to make any difference....until it does, and either speeds up again or dies and wont start. Then the only way to get it to fire back up is to set the carb back to it's original setting. But the saw will not run right at that setting, but it will usually start.

Once in a blue moon I can get it to run ok, get the low and idle set ok, and then try the high side. And no matter what zi do, I cant get it to rev over 9500 rpm. I dont k ow if that is correct or not, but I keep reading that it should run about 13500 rpm.

So, the question is, what the hell am I doing wrong? By the way, I just tried a brand new carb and it's doing the same thing.

By the way, anybody know what the initial settings for the carb below should be? I have been starting with the low side being 1/4 turn out and I have no idea what the high side should be.

View media item 95644
I know the carb shows stops built into the adjustment screws but they have been modified to allow adjustment.

 

[Davefr]

Start with a basics:

- Check the fuel line for leaks or constrictions. Especially where it enters the tank.
- Make sure the fuel filter is in good shape.
- Now check the impulse line and/or boot for any air leaks.
- Check that the air filter is not clogged up with fine dust

If all that checks out and you've tried a different known good carb. then it's time to test compression and inspect the condition of the cylinder and piston.

After that it's time for a pressure and vacuum test to make sure the lower seals are good.

Steve's small engine saloon has some great youtube videos including one on chain saw carb tuning. But you can't tune until you are certain the fuel delivery system is in good condition.

P.S. You should be able to download the owners manual from Stihl and it should give you the get started settings for the carb. Usually they're very close to optimal for sea level.

 

[laser3kw]

When I get an unknown 2 stroke with weird problems, I take the muffler off and look at the condition of the piston, rings and cylinder. Sometimes, the motor gets a dose of straight gas and takes the rings out. Then you fight with it because it has bad transfer due to blow by.
On weed wackers, 9 time out of 10, they have been over heated and the rings are wiped out.

 

[Danny318]

In my saw it was the fuel line. The filter had come off and the line had rotted in some places. Maybe the ethanol is what does it.

 

[M6erfan]

check for air leaks, after the carb.

 

[Mr. VR6]

Slow down. Grab a carb rebuild kit for 5 bucks, watch a YouTube video on the rebuild, and dial the high and low out one full turn each. Set idle to just before chain moves. Done. I’ve rebuilt a lot of saws that people can’t get to run. Sounds like carb diaphragm to me. Carb kit is cheap, start there.

 

[bpjr]

I had a similar problem on a 2 stroke week trimmer. After doing all the normal stuff I took the cowl off and found loose crankcase screws. Tightened them up and problems solved. Its usually fuel lines or primer bulbs but I had a fuel filter in the tank starve low speed enough to make adjusting impossible on a chain saw.

 

[bcschief]

Pull off the muffler and see how it runs may have a plugged muffler.

Brian

 

[Copymutt]

Pull off the muffler and see how it runs may have a plugged muffler.

Brian

X2, seen it many times. Also possible the carb diaphram has hardened from ethanol.

 

[CR888]

'If' your carb has been well cleaned & assembled you need to reset the jetting to factory specs. So turn the H & L ALL the way in gently seating the screws and the back them out to factory spec (will be something like 1 turn each or maybe 1 turn and 1-1/2 turns the other). Then you have a starting point that will start & you can begin to turn the L-speed. Turn it either CW/CCW until you get max idle rpm the richen it a little bringing rpm down. Test throttle response, it should be instant with no hesitation. Then set H last to factory spec (12-13.5k?) and make sure its four stroking so it will clean up under load cutting. Remember fuel circuits are linked so what you do to L speed will effect idle and H speed requirements. You may need to go back and tweak the L after you done the H. Tuning is part pretty easy when you know how to do it so hang in there and learn to do it well, it'll pay off to be a competant tuner.

 

[Robby321]

No comment...wait, as thats the dumbest thing to start out at the END the gas flow FROM THE TANK and related FIRST..and "gotta be the carb" ( and a $20 yard sale?)

 

[Tallpilot]

No comment...wait, as thats the dumbest thing to start out at the END the gas flow FROM THE TANK and related FIRST..and "gotta be the carb" ( and a $20 yard sale?)

People are always giving away small engine equipment at yard sales that they can’t get to run. I’ve seen Honda lawnmowers on the curb for things as simple as a missing wheel nut.

 

[Git]

"Does your chainsaw bog and hesitate? Watch this video to see what may be your problem and how to fix it!"

Hint - he replaces the carb

link to $20 carb
https://www.amazon.com/dp/B06Y61WJ8L/?tag=atomicindus08-20

 

[Jason280]

Check the muffler, impulse/fuel lines, and wouldn't hurt to pressure test the tank and crankcase. I had an 066 with similar symptoms, ended up being the clutch side crank seal...

 

[finn]

Check the fuel lines first. They degrade and crack. Then remove the muffler and clean the spark arrester. They plug with carbon if the fuel mix is too oil rich. Check the piston for scoring while the muffler is off.

Third, do a vacuum / pressure test to make sure the crank seals are good. Leaking seals mess up the a/f ratio and cause a lean condition.

You already tried a new carb, but some of my saws trap fine sawdust in the internal screens inside the carb. Not sure how it gets there, but it’s happened a couple of times on one particular saw. New carb should have eliminated that possibility, though.

 

[DaveInPhilly]

Check the fuel lines first. They degrade and crack. Then remove the muffler and clean the spark arrester. They plug with carbon if the fuel mix is too oil rich. Check the piston for scoring while the muffler is off.

Third, do a vacuum / pressure test to make sure the crank seals are good. Leaking seals mess up the a/f ratio and cause a lean condition.

You already tried a new carb, but some of my saws trap fine sawdust in the internal screens inside the carb. Not sure how it gets there, but it’s happened a couple of times on one particular saw. New carb should have eliminated that possibility, though.

I cut a lot of firewood and all of my saws have been second hand. This is the exact order of operations I would suggest.

Fuel lines, carb, and spark arrestor have been 95% of the problems I have ran into.

 

[classic70]

Alot of good suggestions above, but first I would check spark plug. If it is almost oil fouled you will need to pull muffler and clean spark arrestor first.

 

[M6erfan]

Problem 1, turning the idle screw does not speed up or slow down the saw......until it does! Then it drops from 4k or 5k rpm to 2k instantly and dies. Does this no matter what. If I turn the idle screw in even an 1/8th of a turn from where it is at 2k, it jumps back up to 5k. It's like there isnt an inbetween.

So I get it as close to 2700, 2800 rpm and then go to adjust the low speed, again, it doesnt seem to make any difference....until it does, and either speeds up again or dies and wont start. Then the only way to get it to fire back up is to set the carb back to it's original setting. But the saw will not run right at that setting, but it will usually start.

Once in a blue moon I can get it to run ok, get the low and idle set ok, and then try the high side. And no matter what zi do, I cant get it to rev over 9500 rpm. I dont k ow if that is correct or not, but I keep reading that it should run about 13500 rpm.

So, the question is, what the hell am I doing wrong? By the way, I just tried a brand new carb and it's doing the same thing.

check for air leaks, after the carb.

Run away high idle...
Can't get idle mixture set...
Jetting/tuning is a nightmare...

These are classic symptoms of an overly lean condition. Again, check for air leaks

Check these areas...

• Carb joint/intake manifold
• Cyl head/base gaskets
• Crank seals

Visual inspection tells you nothing. You'll need to block off the intake and exhaust ports and pressurize cyl to 5-7psi and see if it can hold pressure.

Edit: Excellent video here...

 

[Bretny]

Dont waste your money on a carb rebuild kit. You can find oem stihl carbs new on ebay for $19 sometimes.

I have a ms193t that would run like ****...turns out it didnt like 40:1 oil mix i was useing. Spark arrestor was colgged because of it.

 

[JiminAZ]

Yeah fooling with the carb is a fool's errand. A new carb from the Stihl dealer is like $23.

Presuming you've checked the fuel delivery system and you have clean fuel, etc. clean that spark arrestor first. Pull the screen off. Fire up a propane torch and holding the screen with a pair of pliers just put the screen in the flame and burn off the carbon. The screen will glow orange no big deal just burn the **** off. Put it back together and rock on.


A carboned up spark arrestor is consistent with poor high speed performance. It breathes enough to let it idle but the backpressure wrecks it at speed.

This is a regular maintenance issue with Stihl saws in my experience.

 

[SGKent]

That type carb is known to have that issue. I have three or four devices which have that carb (leaf blower, hedger, tiller, etc), and I keep a spare one around. The fuel pump section fails from the fuels. A kit to rebuild it is just as expensive as a new carb. You need to find one with the same linkage as what you have so find the part manual online for your saw., then chase down the part number. Drain the fuel after each use and it will last longer. Look up "Zama carb" on ebay once you have the part number and you will find the one that firs. Most models are only $10 - $20 shipped.

 

[zendriver]

I must have been the only one that read the OP, where he already tried a brand new carb.

IMO, there is no shame, in taking a $300 chainsaw, to a good professional, that knows what the hell they are doing.

 

[freudianfloyd]

Ok, let me add some details to this.

1. I did check the fuel lines and primer bulb and all hold pressure.
2. The fuel filter looks clean, and can easily been seen through.
3. It is getting good spark
4. The carb is new, albeit a chinese knockoff. I went to three Stihl dealers and no one had one or a rebuild kit. The last guy said to just get a chinese one from Amazon, it will be the same anyway.
4. I checked compression and am getting roughly 115 psi. I'm not sure what it should be though.
5. The fuel is brand new
6. The muffler is clear, and I had removed the spark arrestor before I started.
7. The air filter wasnt too bad, but far from new.

All of those things were checked after it had issues starting originally. From the many saws I have had over the years, they always seem to have carb problems, so that is usually where I start.

Like I said, it will run, and sounds good at full throttle, although my tach only shows it going to 9500 rpm.

It just doesnt idle smooth, and it bogs down when I hit the throttle.

 

[freudianfloyd]

I appreciate all the help though guys, and will try some of the other things mentioned.

 

[Davefr]

I must have been the only one that read the OP, where he already tried a brand new carb.

No, you were the second after 20+ replies lol.

Ok, let me add some details to this.

1. I did check the fuel lines and primer bulb and all hold pressure.
2. The fuel filter looks clean, and can easily been seen through.
3. It is getting good spark
4. The carb is new, albeit a chinese knockoff. I went to three Stihl dealers and no one had one or a rebuild kit. The last guy said to just get a chinese one from Amazon, it will be the same anyway.
4. I checked compression and am getting roughly 115 psi. I'm not sure what it should be though.
5. The fuel is brand new
6. The muffler is clear, and I had removed the spark arrestor before I started.
7. The air filter wasnt too bad, but far from new.

All of those things were checked after it had issues starting originally. From the many saws I have had over the years, they always seem to have carb problems, so that is usually where I start.

Like I said, it will run, and sounds good at full throttle, although my tach only shows it going to 9500 rpm.

It just doesnt idle smooth, and it bogs down when I hit the throttle.

115 PSI is very low for a saw with low hours. (assuming your reading is accurate) I would expect more like 150 PSI + or - for a low hour saw.

It's time to pull the muffler and inspect the piston skirt, rings and cylinder wall. It could have been straight gassed or run almost to the point of lean seizure.

Steve will help you:

 

[M6erfan]

Ok, let me add some details to this.

1. I did check the fuel lines and primer bulb and all hold pressure.
2. The fuel filter looks clean, and can easily been seen through.
3. It is getting good spark
4. The carb is new, albeit a chinese knockoff. I went to three Stihl dealers and no one had one or a rebuild kit. The last guy said to just get a chinese one from Amazon, it will be the same anyway.
4. I checked compression and am getting roughly 115 psi. I'm not sure what it should be though.
5. The fuel is brand new
6. The muffler is clear, and I had removed the spark arrestor before I started.
7. The air filter wasnt too bad, but far from new.

All of those things were checked after it had issues starting originally. From the many saws I have had over the years, they always seem to have carb problems, so that is usually where I start.

Like I said, it will run, and sounds good at full throttle, although my tach only shows it going to 9500 rpm.

It just doesnt idle smooth, and it bogs down when I hit the throttle.

115 is pretty low. But it depends on the compression tester used.

A risk of being annoying, i'll say it again for the third time...pressure test the cylinder. Any 2 stroke with unknown issues gets a leak test on my bench, first thing. Period. Reason is, a simple leak test can save you a lot of time chasing your tail. Bottom line is, no-one on the internet, including me, can tell you what's up with the motor. You can diagnose, or chase your tail...

 

[bob15]

115 is pretty low. But it depends on the compression tester used.

A risk of being annoying, i'll say it again for the third time...pressure test the cylinder. Any 2 stroke with unknown issues gets a leak test on my bench, first thing. Period. Reason is, a simple leak test can save you a lot of time chasing your tail. Bottom line is, no-one on the internet, including me, can tell you what's up with the motor. You can diagnose, or chase your tail...

This ↑↑↑↑↑

 

[Wamsutta]

So, the question is, what the hell am I doing wrong?

You're getting the idle speed screw and the low speed mixture screw mixed up; that's your problem. They are entirely two different things for entirely two different adjustments.

One is a mechanical stop for the throttle plate; and the other is a needle that protrudes into a passageway to limit or increase the flow of fuel in the idle circuit in order to get the correct ratio of fuel to the amount of air that's coming in during idle. Somewhere around 14 parts air to 1 part fuel is what you're after.

 

[freudianfloyd]

You're getting the idle speed screw and the low speed mixture screw mixed up; that's your problem. They are entirely two different things for entirely two different adjustments.

One is a mechanical stop for the throttle plate; and the other is a needle that protrudes into a passageway to limit or increase the flow of fuel in the idle circuit in order to get the correct ratio of fuel to the amount of air that's coming in during idle. Somewhere around 14 parts air to 1 part fuel is what you're after.

I appreciate the information, but I am fully aware of the difference between the two. The biggest problem is the chainsaw doesnt respond to any carb adjustment, and then suddenly changes to the extreme, even with the smallest adjustment.

 

[jdl25]

I have a blower that will not respond to carb tuning and it ended up being high and low screws had been over tightened and damaged the carb body.

 

[The Cobbler]

.. the chainsaw doesnt respond to any carb adjustment, and then suddenly changes to the extreme, even with the smallest adjustment.

I'm thinking vacuum leak in the carb , the intake or crankcase

 

[Jason280]

You have to pressure test the crank case/cylinder, as well as the rubber boot that goes from the carb to the cylinder. I'd almost be willing to bet either the clutch side or recoil starter side crank seal is leaking, based on your symptoms.

As far as compression goes, it really depends on the tester and the method. That being said, a lot of the home owner saws don't have really high compression in the first place.

 

[CR888]

Pull the muffler, looky look at the up & down thingie. 'If' its not nice & shiny & with score marks then do a P/V test. Turnie a couple of muffler screws & lots of useful info will reveal itself. 'If' it has piston damage your next job is to find out 'why'. Good news is them saws are cheap/easy to rebuild, you still got a good deal even if the saw seized. But you may get away with a clean of cylinder and new piston/rings.

 

[Davefr]

I appreciate the information, but I am fully aware of the difference between the two. The biggest problem is the chainsaw doesnt respond to any carb adjustment, and then suddenly changes to the extreme, even with the smallest adjustment.

You can't fix a mechanical problem by fiddling with the carb. You're just wasting your time. It's time to move on.

Once again, pull that muffler and have a look inside for possible clues and then be prepared to do a pressure/vacuum test. It's actually pretty easy to do. Those steps will yield the root cause of the problem.

I'd also suggest a trip over to arboristsite.com and see if this model saw has any known issues.

 

[bpjr]

+1 on the Arborsite. Lots of experience there.

 

[freudianfloyd]

Its ALIVE!!!

Well, it runs and accelerates. I took the muffler off and can see some light marks on the piston skirt, but the rings move freely, and they marks arent deep enough to feel. I put a bore gauge in the spark plug hole and didmt see any unusual wear.

I put a new spark plug in it, and replaced the hard plastic o ring between the carb and engine with a rubber one and tightened the carb down more than usual. Set the carb to what is usually ok for initial settings and fired it up.

This time it actually responded to carb adjustments. I got it close, and then took it to my dads who has way more experience tuning saws, and let him fine tune it. It still isnt perfect, but it fires right up and accelerates almost instantly when you pull the throttle. So it's much better than it was.

It will become 4th in line of saws I grab, so I'm not too concerned about it, plus I paid only $20 for it.

Either way, thank you all for your input, I'm going to leave it as is and try running it some more and hopefully it has finally been fixed.

Plus I just got a good deal on a top handle Stihl at a yardsale today that I will be jumping into soon, so this saw will go on the rack.

 

[laser3kw]

and replaced the hard plastic o ring between the carb and engine with a rubber one and tightened the carb down more than usual.

smoking gun? Best guess for the air leak theory.
the peek-a boo on the cylinder was telling. The marks on the skirt may be from a straight gas episode.Not enough to kill it, but didn't help either.
congrats on saving another orphaned piece of power equipment.

 

[theoldwizard1]

The REAL EXPERTS are over here ---> Arboristsite.com/Chainsaws

 

[freudianfloyd]

The REAL EXPERTS are over here ---> Arboristsite.com/Chainsaws

I have visited the site many times, I might need to become a member.