Was Milling this last week and...(chainsaw issue)

[AaronB]

I was milling this last week and all of the sudden the saw would die when at full throttle or die if it would have any type of load put on it at half throttle. Basically it would start and idle just fine, and even sounded good at half throttle but when I would push to mill it would die, and if I tried to go to full throttle it would die. After it died I never had a problem re-starting it.

At first I thought it might be the fuel, but my other saw (same brand) ran just fine with the same fuel, then I thought it might be the fuel filter, cleaned it and even changed it.

Also, this happened Wednesday morning, then ran fine after lunch for a while, I didn't mill Thursday, when I went to mill Friday morning the saw ran just fine for a while, until late afternoon, but then it started dieing again so I stopped, started the saw Saturday morning just to see if it would work (not milling) and it worked fine at full throttle. Its almost like something quits working when it gets hot.

What might cause this that I am over looking?
I am pretty new to saws so it might be something simple, but thought I would ask and see if there are other things to change/try/clean.
Thanks

 

[andrethegiant70]

Do the easy stuff first

Milling is VERY hard on saws, it's not hard to kill them. Pull the muffler and check the piston to see if it's scored. Its definitely a possibility. If it is NOT scored, you might pull it over some to see if you've lost a substantial amount of compression, or if you have a compassion tester, use that. Beyond that, I'd check your fuel filters, your carb tune, and spark. I HAVE seen saws that, when they got hot, their ignition systems cut out. So it is possible you're losing an ignition which, relatively speaking, would be good news.

Good luck, report back.

Edit: it would help if you told us the type of saw, how new, type of wood, and how big. How was it running before it misbehaved. Any work done on the saw previously?

 

[TPA]

Maybe vapor locking?

 

[AaronB]

Edit: it would help if you told us the type of saw, how new, type of wood, and how big. How was it running before it misbehaved. Any work done on the saw previously?

Saw: Stihl 660, 3 yrs old
Wood: White Oak, 22" diameter
Running before: I used it the weekend before and did not have any issues, ran it through three 8' logs and everything ran fine.
Work done: none

My FIL and I finally took out and cleaned the spark plug (don't have a new one) and it ran fine after that, but it had been sitting overnight so it was cold, so it probably would of ran fine had we not cleaned it, but I didn't get to mill with the cleaned spark plug.

 

[excess650]

I've had an 066 run erratically and found the sparkplug boot vibrated off the plug, and I wondered how it ran at all.:msp_confused: My 660 was sometimes hard to start after getting hot, so I got another coil for it out of suspcion. I've not run it enough since to determine whether I still have a gremlin or not.

 

[brookpederson]

I had i 440 once that had the same symptoms. It might be your fuel line in the gas tank, the hose was old and would collapse on itself when running full throttle and cut the gas off. Hope it's supptin easy like that. You could try the chainsaw forum of this site too. Those guys over there effin wizards when it comes to fixin stuff good luck

 

[MHouse1028]

sounds to me like a tear in the intake boot ...i had the same issue idled fine but when a load would put on it it would die rite out..

 

[AaronB]

sounds to me like a tear in the intake boot ...i had the same issue idled fine but when a load would put on it it would die rite out..

What bothers me and my FIL is that it doesn't happen all the time, its not constant, it can run fine for an hour or 2, maybe even 4 before it starts doing it.

 

[golddredgergold]

I am new but not new to chainsaw engines. FIRST put a new spark plug in and try again! Most issues like this come directly from the plug going bad. The carbon core of the plug goes bad inside. Not the spark tip but the carbon core. They break down and cause crazy things to happen. Seems simple but 9 out of 10 times the plug is bad. You say you cleaned it. Ran fine. But guess what after it heated up the carbon inside lost connection and you got a weak spark after heat and vibes. Go buy a new plug and a spare while you are there.

They put a new water line outside my home a few months back. I sat back and watched them fight a Stihl with a cutting wheel not start at all for 2 days. They pulled and pulled by several guys and wiped them all out, then went to the truck in my yard and worked on it and it would not start. I finally walked out and asked what the issue was. They said it is our only cutter and it will not start. Ran fine then would not run full then stopped.I said Has it got spark. They said yes and fuel wet plug. I said plug is bad! They said NO it has spark and we cleaned it! I said plug is bad. Might have spark outside the hole but not in. Of course I got a look like I just called them all stupid. One rolled his eyes. I insisted plug was bad and they said well we do not have another one now to try as he began to put the bad one back in the saw. I said wait one minute. I went to my shop grabbed a new plug and took it out. Handed t to them in the box and the fellow opened and put it in the saw. Joking he said I bet it will not start. Guess what first pull it fired up. I said to the fine men who's laughing now!:msp_tongue: He says what do we owe you for the plug? I said $35.00.... He says they are only like 5 bucks. I said I know 5 for the plug and 30 for my mechanic time to diagnose your issue! To say the least they where happy and back to work! I only took the money for the plug. They brought me a beer for the help.

LONG story short put a new plug in first. you might be surprised and save yourself many hours of work and heartache.

 

[andrethegiant70]

That's good news...

If it runs well when it runs, your saw is basically sound, though you obviously have a niggler. These gents have correctly suggested some things you can try. I personally feel you should start with the ignition. I would closely inspect your wiring to see if anything is grounding out. Swapping plugs is a cheap and easy thing to do, there have been many plug failures with symptoms like this. Lastly, you might find an extra coil to swap in for troubleshooting.

If the saws cuts out and won't restart at some point, I'd pounce on it, pull that plug wire and see if I had spark.

To be fair, these are just some ideas, There's certainly a possibility you have a non-ignition problem, but you're going to have to start somewhere and get a little scientific about it. For the saws I use a lot, I keep spares parts around for just such problems. Truth be told, I keep doubles and triples of the saws. At any point, I can take a verifiably working part and slap it on there for troubleshooting purposes. I do admit that is overkill for a normal person, though.

I wouldn't feel too annoyed with the saw... After three years of milling, components could certainly begin to fail. You might want to just renew the fuel system ( carb kit, fuel line, inspect boot, change the filter) on general principle. You owe it to that beast.

Good luck and let us know what you find.

 

[DSS]

I had a saw with bad a/v bushings that would quit when you pushed a certain way. It was twisting and pinching the fuel line. Just something to think about.

 

[john taliaferro]

to expensive of saw to burn down find and fix the problem before you :taped:

 

[mtngun]

Check for a torn fuel line or clogged fuel filter. Carb kit. If it's starving for fuel, your engine will not survive much longer.

 

[glennschumann]

The other fuel filter...

One that got me in a similar situation was the screen inside the carb that acts as a secondary fuel filter. Take the sides off the carb, and you will find one side with a screen pressed into a hole. it may be filled with fine sawdust that is so fine it looks like a gel. If so, spray that out with a little carb cleaner, and give it a second try. The 'gel' will settle away from the screen when the saw sits, but over time during running, it will eventually plug up the screen and cause fuel starvation problems like this. Could be the plug too. Don't go just getting another plug, however. Make sure it is the right one if a previous owner put the wrong one in. Been there too...

Schumann

 

[discounthunter]

hopefully its an easy find/fix. i would however pull the muffler to look at the piston. it is the heart of your saw,and very pricey. if its fine then look at everything else.

 

[griffonks]

hopefully its an easy find/fix. i would however pull the muffler to look at the piston. it is the heart of your saw,and very pricey. if its fine then look at everything else.

I would spark test it, pressure test it, compression test it, then work thru the fuel and air supply. Make sure the case isn't leaking....