I have a stihl 391 and it is not cutting good. The nose/top of the saw is cutting fine but when i go to use the part of the saw nearest the saw itself its as if it loses power and nearly stops cutting. would it have something to do with compression? i have been using this saw for about 10 years now and never had any problems with it.
saw not cutting good
- Thread starter viztopia
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Check and see if there is a screen in the muffler exhaust outlet. When the screen carbons over and begins to close up you will lose a good bit of power. 10 years is also time for a tune up, new fuel lines, carb diaphragms, filters, plug etc.
nmurph
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:agree2:
This would be a good place to start although I don't know why where on the bar the cutting is being done would matter.
BTW, you saw can't be 10YO and be a 391 as that model has only been out for a couple of years. It is more likely a 390 which is a totally different saw.
This would be a good place to start although I don't know why where on the bar the cutting is being done would matter.
BTW, you saw can't be 10YO and be a 391 as that model has only been out for a couple of years. It is more likely a 390 which is a totally different saw.
D&B Mack
Sawin Wit It!
This is totally random, but I have personally seen it, so worth a shot. I'm throwing this out there, because I am not sure what you mean by:
is it bogging out, or throttling down?
If it is bogging out, your rakers could be filed down too much. When you are cutting on other parts of the bar, the saw will force itself out of the cut and keep the RPM's up. But when you cut on the bottom near the saw, the saw dawgs in and it cannot back itself out of the cut and it is trying to take too much of a bite for the saw.
If it is throttling down, you may a fuel line issue. Your saw digs in the most when cutting on the bottom near the saw. It will suck the most fuel at this point, if your filter or line is partially clogged, your saw could be shorting itself on fuel supply. It can also be, as previously posted, the muffler screen.
is it bogging out, or throttling down?
If it is bogging out, your rakers could be filed down too much. When you are cutting on other parts of the bar, the saw will force itself out of the cut and keep the RPM's up. But when you cut on the bottom near the saw, the saw dawgs in and it cannot back itself out of the cut and it is trying to take too much of a bite for the saw.
If it is throttling down, you may a fuel line issue. Your saw digs in the most when cutting on the bottom near the saw. It will suck the most fuel at this point, if your filter or line is partially clogged, your saw could be shorting itself on fuel supply. It can also be, as previously posted, the muffler screen.
SawTroll
Information Collector
Yes, it can't be a 391 if it is 10 years old.
nmurph
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A tiny hole will cause a saw to bog under load.
apologies - your right it is a 390!
You have also posted about having problems with a 260, an 039, and a 240. Did you get any of them running?
foxtrapper
ArboristSite Lurker
When you set the spikes and lever the saw over, you can really cause the heel of the bar to dig in hard, making the engine work very hard.
Out at the tip of the bar, you've very little leverage, and can't force the bar into the wood, so the engine won't work as hard.
That'd be my take on it.
I am looking on ebay for piston/cylinder kit for the 260. my brother in law is after replacing the piston on a similar sized one so he is going to help me. the prices of genuine parts are ridiculous. a local dealer is doing a special on the ms181c and it is twice the price of the genuine parts so i think i would be better off just getting a new saw than buying the genuine parts.
the 039 is going fine, probably the most reliable of the whole lot.
I have a magnum 460 which is a brilliant saw to have also.
at the same time i am thinking i have too mant saws to look after. always something wrong with one of them.
thanks for that. I would imagine thats what it is. more than likley noen of the above have been done in a while.
nmurph
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He said he had been using this saw for 10 years, I was assuming he would know that difference.
Ifishsum
ArboristSite Member
Could it be that the bar is worn at the base and causing the chain to tip and bind?
sodbreaker
ArboristSite Operative
I had a 25 inch bar on a 391 that would act pretty similar to the OPs problem. Turned out the bar was bent in just the right spot that I could cut with the tip no problem but when I tried to cut bigger wood or try to cut closer the the power head. It would be cutting at the bent spot, pinch, bind and bog down the saw. New bar and now she runs perfect again.
SawTroll
Information Collector
A 390 won't cut well for its size, regardless what you do to it - it just is a cheaply made excuse for a saw.
Anthony_Va.
XPW Fan Club
I think it's in the bar. Need to file the lip off the edges if theres one built up. Either that or buy a new bar.
i am just ordering the parts for tidying up my saw. I am ordering the following;
1) new oil and fuel filter
2) new spark plug
3) new diaphragm
4) new fuel line
is there anything else that you would recommend getting as part of normal maintenance?
only got round to doing what i had originally intended doing with my saw. I did the following;
- changed the fuel filter and fuel line
- changed the oil filter
- changed the spark plug
= changed the fuel filter
- changed the diaphragm on the carburetor
and no my saw wont start. ok it hasnt been used since last september but i am trying to figure out where i went wrong. there has been no fuel in it since today. I dont think that the changing of the spark plug/oil filter or the fuel filter would stop it from starting. So that would leave it down to the fuel line and the diaphragm. I think the only way that the fuel line would stop it from starting would be if it was block which would be very unlikely. the only other thing is if i put on the diaphragm on wrong but this was straight forward and even if i did this wrong it should probably still start. any one any ideas?
- changed the fuel filter and fuel line
- changed the oil filter
- changed the spark plug
= changed the fuel filter
- changed the diaphragm on the carburetor
and no my saw wont start. ok it hasnt been used since last september but i am trying to figure out where i went wrong. there has been no fuel in it since today. I dont think that the changing of the spark plug/oil filter or the fuel filter would stop it from starting. So that would leave it down to the fuel line and the diaphragm. I think the only way that the fuel line would stop it from starting would be if it was block which would be very unlikely. the only other thing is if i put on the diaphragm on wrong but this was straight forward and even if i did this wrong it should probably still start. any one any ideas?
You could try pouring a bit of fuel mix into the carb and if it fires your not getting fuel to the cylinder. Or check the spark plug and if it's wet your getting too much fuel to the cylinder. Your carb needs to be done properly. On the metering side it goes carb body-gasket-diaphragm-cover and on the pump side it goes carb body-pump diaphragm-gasket-cover. Also the metering lever needs to be set to the right hight. Make sure your air filter is clean and check the exhaust screen. If your bar is still an issue you could try one off your 039.
