This is my day to ask questions, I guess. I have a Stihl O21 chain saw for chopping up windfalls etc. I've had about it 5 years. Reasonably good care, clean fuel, springtime tuneups etc. Here's the thing; this year, it will start and run and, if you keep it running, it will cut. If you shut it down, it will not restart for several hours not matter how much you pull that damn rope. Wait 'til the next day, start it up and use it, all is ok unless you let it stall, then you're screwed for another day.
I took it to Ace Hardware where I bought it and the helpless hardware man looked it over and sent it back to me with a tag that said it "had serious problems" and would "cost more to repair that to buy a new one". Of course, the helpless hardware man was unable to elaborate on the "serious problems" afflicting my saw.
Anyone have any ideas? I know it's not much to go on. Thanks!
When you turn it off the cooling of the engine stops and components like the coil or electronic ignition will heat up further . These could malfunction in the heat. See if you get sparik when it wont start. If you get spark then its either flooded or starving for fuel.
Start with the basics. Is the air filter clean? Are the cooling fins clean? Replace the spark plug. Check the fuel line for any deterioration. The fuel line gradually deteriorates which can result in a condition where it can just barely draw adequate fuel while running but when it shuts off pull starting it won't draw enough fuel. This can be worse when the saw is hot which makes the fuel line softer and more prone to air leaks but when the line is cold it's stiffer and may seal enough to start. This happened to my Stihl 021.
Has the saw run leaner lately? (less blubber sound and higher RPM)
The saw needs fuel and ignition. Which isn't it getting after it stalls. Check for spark and check for a wet plug. Squirt some gas into the cylinder after it's stalled. Does it fire?
If your problem happens to be the ignition coil you should be covered since Stihl warrantees it for life.
How's the compression? Pick up the saw by the pull cord. Can you pick it up with only a very gradually lowering. If so the compression is fine.
Pull the muffler and inspect the cylinder with a small flashlight. Is there any scoring of the cylinder. Can you still see the factory cross hatch pattern??
I seriously doubt the Ace Hardware "shelf duster" properly diagnosed the saw. I wouldn't write it off as yet. Do as I described and report back.
You might also want to search the chainsaw forums at
If you are into diagnosing and fixing things (in particular small engines yourself: The other suggestions in this group sounded all pretty good. Do as much as you are comfortable with.
I'll add one of my own. First, gasoline when stored tends to clog fuel lines and carburators. Take the fuel line and the carburator apart, wash all the pieces nicely in clean fresh gasoline, and blow out the nozzles and the hoses with compressed air. WARNING: Doing this carelessly or indoors or near sources of ignition is a sure way to die or burn your house.
Second, the formulation of gasoline has changed considerably in the last few years, at least in urban areas (because of smog laws). Also, carburator adjustments don't last forever; you might have knocked an adjustment screw, or something has come loose. Your carburator might be terribly misadjusted, and be unable to run in idle when the saw is really hot (and it gets hottest AFTER you turn it off).
Now the really important one: Clearly, the repair person you brought it to HAS NO CLUE. There are many possibilities (lose ignition wire, sick spark plug, fuel line slightly leaky, cooling air clogged, carburator needs to be adjusted, air filter clogged, choke got stuck and so on) that a good technician can fix in a few minutes of work, and with no or very cheap spare parts. Last time my saw (a Stihl 26) was behaving similarly sick (ran OK when cold, barely ran and was very weak when hot), all it took was a new spark plug and a good adjustment, at a cost of less than $30. While you are at it, unless you are REALLY good at sharpening your chain, have them sharpen it for you (typically costs $10); this makes a huge difference. Few amateurs can get a chain really sharp (I can't either).
Run, don't walk, and find a COMPETENT Stihl repair shop. One that is licensed by Stihl, has the sign hanging outside, and the whole place is full of chainsaws (in particular, a place where lots of landscapers or tree professionals bring their gear for repair).
If you are in the southern San Francisco Bay area, I can make a few suggestions (Gardenland in Campbell, TrueValue Hardware in Boulder Creek). Elsewhere, look in the phone book, call a local landscaping company, or call Stihl.
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