Saw didnt shut off?

[Jungleman]

So here's a first for me and I wanted to know if anyone knows why this happened.

Was running my 066 with a 25" bar just cutting logs into firewood. It started to hiccup a bit so I pulled it out of the cut and was looking/listening to hear anything when suddenly it went FULL THROTTLE for about 5 seconds. Now within 1 second I checked the throttle to see if maybe it was stuck and it was fine so I turned off the saw in second 2. So it ran for about 3 seconds it ran at full throttle even though it was off.

Never seen that in 20+years of using chainsaws. Anyone know what it might be? I'm gonna take a wild guess and say somehow some fuel got stuck in the carburator and was somehow forced out in an unstoppable surge. I dont know.

Could it have anything to do with my air filter cause I noticed it had an opening allowing some dust to get in close to the carb intake. I'm not using the saw till my new air filter arrives.

Thoughts?

 

[Jungleman]

And before any asks, yes the kill switch wire was still in place with its oval shaped metal tip and it made connection to the little metal plate. That is not the problem.

 

[Whiskers]

Once the kill switch makes proper contact It should shut the saw down no matter how much fuel.

Was the trigger functioning normally, sounds like you’re no newb so you’d notice.

The thing that makes a saw go full throttle is a sizeable air leak. I’d check the intake boot for cracking first. If a saw is pull on while stuck it can tear the boot. If you start it again and it revs away I’d suspect an air leak. Pressure and vac test will tell you if that’s the problem.

 

[Al Smith]

I don't know about the saw in question but I did experience a torn intake boot on an a Stihl 038 Magnum on the under side . If the condition was just right that thing would run probably 7-8000 RPM with the throttle completely closed .Took me a while to figure it out .Turns out it was the top left annular buffer gone back allowing the engine to rotate in it's mounts thus tearing the boot

 

[Jungleman]

Sounds like I'll be taking a look at the intake boot. Thanks.

 

[Al Smith]

What happens if the boot does get torn is it sucks in a huge amount of air which will really draw on the low speed jet .In that event the low speed becomes the high speed jet .That thing could probably rev up like a model air plane glow engine .I never hit the throttle to find out .That pot licker might come apart like a dollar watch .Scares me and I'm fearless .

 

[Whiskers]

Impulse line is another common area to introduce an air leak. After that vac testing is in order.

 

[Jungleman]

So here's my latest dumarse question of the day. I got my new filter and I was wondering if I still need to squeeze in that black plastic piece inside the green foam? My guess is no.

 

[Whiskers]

I don’t know if it’s a one or another kind of thing green foam or plastic baffle.

Did you find out what was going on with the saw originally?

 

[Jungleman]

It's a new AM filter that has a green foam inside of it. The old OEM filter didnt have the foam and instead had that black plastic piece inside of it.

To answer your question, no I have not figured out why it wouldn't turn off. I took this saw apart back in January to put in a new piston. I also replaced a lot of rubbers including the impulse line and boot. They were also AM parts but I cant imagine they would fail so quickly. I still plan on taking a look at them when I have some time to open it back up.

I dont have a vacuum tester and wifey will have my a$$ if I buy one right now. Money is tight.

 

[Yukon Stihl]

AM rubber can fail that quick.
What piston?
Go back to OEM then your troubles will decrease and you wouldn't have to ask questions about weird foam and where it isn't supposed to be..

 

[Wonkydonkey]

That foam is a baffle..stihl used them with some filters iirc

 

[Bigmac]

I would as others have stated to check your intake boot and inpulse line, that’s free. The foam is the old style spit back style, just discard and run the black plastic one

 

[Wonkydonkey]

Here’s a pic from the 440 ipl.. it’s used in the hd filter which has a felt prefilter but not used the hd2 filter... your have to compare ipl as the filter is used over a few saw models...

however, don’t forget you will need to retune/tweet the carb,, for the change in filter design

 

[Jungleman]

Here’s a pic from the 440 ipl.. it’s used in the hd filter which has a felt prefilter but not used the hd2 filter... your have to compare ipl as the filter is used over a few saw models...

however, don’t forget you will need to retune/tweet the carb,, for the change in filter design
View attachment 238811

Thanks wonky. That's a great picture right there.
I might be able to check the saw tomorrow night, I'll update after I check the impulse and boot.

 

[a. palmer jr.]

Check for anything that would cause an ultra lean condition, which created a hot spot in the combustion chamber which allowed it to run without any spark. I had a Honda CR250 once that did that and I had to jerk the carburetor off of it to get it to stop running...it turned out to be a cracked intake..

 

[Jungleman]

I dont see any holes or cracks in the boot or the impulse line. Guess I'll run it some more and if it happens again I'll just buy new ones since the general agreement is that it has to be one of those two things.

Many thanks.

 

[Wood Doctor]

I think perhaps you needed to change the title of your post to "Saw didn't slow down to idle." Shut off implies that the on/off switch did not kill the engine. I believe you let up on the throttle and it stayed at WOT for awhile. That could be caused simply by the throttle rod failing to detract quickly when you let up on it.

 

[Bigmac]

I think perhaps you needed to change the title of your post to "Saw didn't slow down to idle." Shut off implies that the on/off switch did not kill the engine. I believe you let up on the throttle and it stayed at WOT for awhile. That could be caused simply by the throttle rod failing to detract quickly when you let up on it.

I was about to give some similar advice on the throttle linkage, and if that’s not it I would check the PTO side crank bearing for play by checking to see if the clutch moves up and down.