Chainsaw fouling plugs

[BIGChrisNH]

So my Stihl 271 Farm Boss has served me well since 2015. In recent years, it has been fouling plugs fairly frequently. The saw does sit more often now because of my two other saws. I have been using the 271 to try to learn to tune. I am not skilled at that yet but I have done the basics like setting the idle, and messing with the low jet until the saw stalls, then adjusting back up until it runs well, and takes off good with a throttle blip. Anyway, since I am not good at this I wanted to ask those of you who are. The air filter is brand new, the spark arrestor is clean, the fuel line is new, the fuel filter is new, the gas is fresh, and I buffed the spark plug with some fine grit sand paper to get it running again as it was dying right after firing up. I got it running just fine.

My question is, if the saw is fouling plugs I'm assuming that it is running too rich. Am I correct in that I need to tune it leaner? I'm trying to learn this skill but it's tough to learn from the internet and not a person. There is an old time saw mechanic near me with a wonderful reputation that I can take the saw to and have him tune it. I also may ask him if he would consider teaching me, though he's somewhat gruff and may tell me to bug off, but that's fine.

Anyway, what do you all think about the plugs fouling without a ton of use? Is the carb running too rich? Just trying to learn more about 2 cycle engines here, appreciate any feedback.

 

[StoveInNH]

I assume the plug is black when taking it out? Should be a light brown/tan.

Black is too rich. You can increase the air or decrease the jet size.

But the real question is what changed? If the jetting is as-purchased, it shouldn't need to be changed (unless in a temperature extreme).

Does the saw have a choke? The problem might lie there (choke not disengaging).

Your problems will likely go away with a carb rebuild (i.e. a cleaning). But if you have to pay for it, the cost might be not much less than the saw is worth . . .

 

[EbS-P]

Do you have a tach?? I tried by ear I’m not good enough yet. Had my Ryobi sounding great At 16k RPM. As a complete amateur I like having the tach.

 

[Woody Stover]

Did you try a new plug yet?

 

[Jags]

I have never had good luck trying to revive a fouled plug. Try a new plug. Run it for a brief time and see if it is still fouled. If it is then yes you are running too Rich.

 

[ABMax24]

I've cleaned them with a propane torch, get the electrode and ground hot to burn the junk off, same thing the engine does continuously when running properly.

What's your oil mix ratio and what oil are you using? Generally these days I find fouling of plugs to be from oil and not gas.

 

[BIGChrisNH]

I have not tried a new plug yet, but I was able to get the saw running again by cleaning the plug that's in there now. The plug wasn't black like I've seen at other times in other small engines, but definitely darker brown, enough to keep the saw from running. This plug is about a year old, and the saw has not been used much, only a few times probably. That's why it's strange that the plug is fouled already.

I do not have a tach, but I will order one. I have a new plug on order and I know it will run good after that is installed. Oil is Husqvarna XP+ synthetic blend 2 stroke oil. I mix at 40:1 for all my 2 strokes.

I will run it for a while with the new plug and then pull it and check it. If it's getting dirty then I'll know I'm running too rich. This may all be for not anyway, I may trade the 271 and the 250 for a 261, but I want the saw running well when I trade or sell it.

 

[ABMax24]

Check your plug wire and pickup to flywheel gap, either of those could cause weak spark that appears like a fouled plug.

 

[BIGChrisNH]

Check your plug wire and pickup to flywheel gap, either of those could cause weak spark that appears like a fouled plug.

thank you.

 

[ericm979]

I've cleaned them with a propane torch, get the electrode and ground hot to burn the junk off, same thing the engine does continuously when running properly.

I have cleaned plugs in a number of ways. But even if they work for a while, they still foul easier than a new plug.

 

[Isaac Carlson]

If it quits right after startup, check your fuel lines. One could be damaged or kinked. It is rare that I see a fouled plug.

The idle jet should be set so the engine idles the fastest. Adjust it rich until it drops off, then slowly turn it back lean until it speeds up amd then starts to slow down again. The fastest rpm it the spot.

The high speed jet should be set to the engine runs fast and has just a little roughness to it. It should sound like the rpm is fluctuating just a little back and forth when the saw is running wide open and it should smooth out in the cut.

There are saw tuning videos and soundtracks online that can help.

 

[spuldup]

Before tuning rule out clogged fuel lines, leaking intake boot or impulse line. Check for visible spark by placing the plug on the head and cranking it over. You will want a new plug, name brand. Random brands on Amazon throw another unknown into the mix.

I know you can use google but this man will show you basically anything you need to know about a saw: Tinman's Saws

 

[ericm979]

If it quits right after startup, check your fuel lines. One could be damaged or kinked. It is rare that I see a fouled plug.

The idle jet should be set so the engine idles the fastest. Adjust it rich until it drops off, then slowly turn it back lean until it speeds up amd then starts to slow down again. The fastest rpm it the spot.

I find that saws work best with the low speed mixture set a little richer than fastest idle, so it drops a couple hundred rpm from the high point. They start easier and there's less lag when you open the throttle. The tuning procedure in Stihls workshop manual also sets the idle mixture slightly rich.

It's easy to hear four stroking if you know what to listen for. It's a sudden pitch change in the engine note. I like my high speed tuning so the saw runs crisply under load but if you lift in the cut keeping the throttle open, it four strokes. Whaahhh-uhh.

This is far richer than a motorcycle racer would tune their engine but it's safe.

 

[BIGChrisNH]

If it quits right after startup, check your fuel lines. One could be damaged or kinked. It is rare that I see a fouled plug.

The idle jet should be set so the engine idles the fastest. Adjust it rich until it drops off, then slowly turn it back lean until it speeds up amd then starts to slow down again. The fastest rpm it the spot.

The high speed jet should be set to the engine runs fast and has just a little roughness to it. It should sound like the rpm is fluctuating just a little back and forth when the saw is running wide open and it should smooth out in the cut.

There are saw tuning videos and soundtracks online that can help.

Thank you this is great information. I've been watching lots of videos and none of them were really helpful until I saw this one

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. This really helps it make sense. I love Buckin Billy Ray's videos but I watched a tuning video of his and didn't learn a thing.

 

[BIGChrisNH]

Before tuning rule out clogged fuel lines, leaking intake boot or impulse line. Check for visible spark by placing the plug on the head and cranking it over. You will want a new plug, name brand. Random brands on Amazon throw another unknown into the mix.

I know you can use google but this man will show you basically anything you need to know about a saw: Tinman's Saws

Thank you for that I will check out that link. Appreciate you posting it. I know it's not the fuel line as the fuel line is new. Not sure about intake boot or impulse line. I have a new Bosch plug coming to me and the saw is running good again with a cleaned plug. I need to figure out why the plugs are getting dirty.

 

[BIGChrisNH]

Before tuning rule out clogged fuel lines, leaking intake boot or impulse line. Check for visible spark by placing the plug on the head and cranking it over. You will want a new plug, name brand. Random brands on Amazon throw another unknown into the mix.

I know you can use google but this man will show you basically anything you need to know about a saw: Tinman's Saws

That is a very good video as well. I bookmarked that one. Thank you.

 

[ABMax24]

Thank you for that I will check out that link. Appreciate you posting it. I know it's not the fuel line as the fuel line is new. Not sure about intake boot or impulse line. I have a new Bosch plug coming to me and the saw is running good again with a cleaned plug. I need to figure out why the plugs are getting dirty.

I've always had good luck with NGK, but the Bosch are supposed to be good too. Just make sure you check the gap on it before install.

In hindsight, maybe the gap is wrong on your existing plug?

 

[Isaac Carlson]

I side gap mine. It gives a little more pep.