Probably the old flywheel has drifted out of the woodruf key on the crankshaft.
You will get a spark even if this happens, but it will not be at the right position of the piston.
The engine will not fire if this happens.
This is not supposed to happen in normal cases(the drifting flywheel).
On the blower it could happen if any solid objects are sucked in by the fan, especially when the blower is being started up with it placed on the ground, and if you happen to rev it up.
Check the fan and fan housing for any impact marks. If there are any, maybe this is what happened.
Maybe.

What you say makes sense, but there is no doubt in my mind that the repairman would have found that. He was stumped himself. He couldn't explain it.

Sounds right to me, the timing was off, which made everything APPEAR normal, but it was actually not correct. thus a replacement flywheel fixed the problem completely.

Ask to see the old flywheel.....

Fish

I have been stumped by this same problem a couple of times.The probable method to confirm what I said would be to use a timing strobe, the kind they use on cars.But I dont know how one rigs it up on a blower running on a 2 stroke engine, with the power coming out of the ignition module.
The easiest would be to compare the old flywheel against a new on with both pile on each other, with the key groove aligned.
Then examine the position of the magnets.A minute twist out of the ordinary will cause the ignition timing to change.
If my impact therory is right, the timing would retard.

Joseph

Hey Joseph, long time, no chat......

Hey Wayne, Is your fuel line now a bright green color?

How about a model number, we need to know.
If it was the flywheel, then the built in key must have
been sheared.
If not, then the magnets mysteriously lost their magnetic charge, which only happens near Bermuda.
Fish

You guys sound like you know what you're talking about. I talked to the repairman and it was NOT the flywheel key, but it was firing out of time. I knew if it was something simple, he would have found it quick. He believes it got hot or for some other reason, shorted out inside the electronic module in the flywheel, or something to that effect, changing the firing timing. This guy is not a parts replacer, he is a real expert and was at his wits end to try to figure it out. Any way, he got it running better than it did when it was new. He finally replaced the flywheel assembly as it was not servicable. (Incidentally, the last time it was used before it shutdown, my grandson used it and ran it for some time, a couple of hours, at about 1/2 throttle to cut down on the dust. Maybe that caused it?

The flywheel is a large aluminum wheel with magnets cast into it, nothing else, The key, whether a separate
woodruff key, or a notch cast into the aluminum, holds
the flywheel in place while tightening the flywheel nut.
So if by replacing the flywheel, it cured the problem, then the key was most likely sheared. Nothing mysteriously scientific about it. Like I said, ask to see the old flywheel.
The only times I usually have to replace a flywheel, is
when someone damages it by not knowing what they are doing.
Broken fins from a screwdriver stuck in them, while
trying to loosen the nut. Or running the unit with the
flywheel nut not on tight enough and shearing the key.
Or overtightening and splitting the metal.
But anyway, the flywheel is just a big aluminum disc
with magnets, no more, no less.
Fish

I'll take your word for it, you can't prove it by me. The guy tried to give me an explanation of what he thought it might be, that I guess I misunderstood. I DO know that he said the key had not slipped. But...maybe it was so simple and he wanted to charge me a lot......Hmmm...Anyway, it runs good now..Thanks guys for all the input. Just for the record, I'll go and check the model and get back to you and let you know. I've always had a lot of confidence in the guy, never had any questionable experiences before.

Stihl has had problems with their coils,not flywheels, losing timing. They have multiple steps in timing depending on rpm and the things pop diodes or something. Some will start but not come off of idle because they're stuck on start up retard. Others just won't start at all because the whole thing is daffy. Still shows perfect spark on a tester but the timing is way off base.

I'd bet he replaced the ignition coil and not the flywheel and decided to up his profits by telling you the flywheel was bad. Stihl has a life time warranty on the coil, you do have to pay labor after the regular warranty is up but the cost of the coil is paid by Stihl. So, he charged you for a flywheel which he didn't replace, replaced the coil which Stihl paid for and charged you 120 bucks to replace the coil. Yeah, a back pack takes a while to do but not that much.

You got ripped dude.

Thanks, You may be right.. I may try to do a test on this guy just for the heck of it. Do a set-up on something and see what he finds. I didn't know all that about the coil..Makes sense though. If he got paid from Stihl and me, he made off like a bandit. Thanks for the info. I'll know better next time.

You might call the Stihl distributor and talk to the area
saleman about it. He could probably run your model/serial number to see if any warranty claims were filed.
Nevada and I both are Stihl mechanics, and we do not
like people giving us a bad name. But to be fair, he may
have just not made himselve clear on the explanation of the
work performed, most mechanics I know were not English/
Communication majors.
I try to explain what I have done to customers, but sometimes the customer and I do not mesh just right.

There are bad/crooked mechanics out there, just as in
any field. I feel the ones that post here are likely honest
just trying to help others for whatever alterior motive.
I just do it for the chicks, they just dig a 43 year
old, fat, lawnmower/chainsaw mechanic.
Fish

I'd like to believe that is the case. This is a NICE guy. Incidentally, I BELIEVE in Stihl products. ( 3 saws-O-51, O-41,and O-28, 1 string trimmer--the one with handlebars, 1 backpack blower and 1 hand held blower-and I'm not a pro landscaper)
BTW The only chicks I have anything to do with now are one wife and 40 hens. Hey, the hens lay eggs and the wife bakes cakes.........TOO OLD

How good is Stihl?

Sounds to me that you had a plugged exhaust screen it happened to me on mine !!! quick fix

I might have a similar problem with a freebee. I acquired a Stihl BG 61 last year from a garage sale. The guy said it quit running so he was just going to throw it out. I am just now getting around to seeing if I can fix it.

It appears to have good compression. I put in a new plug and it has a strong spark. I have removed the screen in the muffler (cleanest one I ever saw). I even put new mixed gas in both the carb and the spark plug area.

Even with a little mixed gas poured straight into the plug, I still can't get it to fire.

Is there any way to test the coil? Thanks

My problem is an easy one. I can't remember how to start my well used Stihl BR420 I bought off the internet last fall. Thet told me there was a sequence I should use on a Stihl, because I could not start the damn thing. Once they told me how to do it, she fired right up! Now I have forgotten the magic sequnce and here I sit on a beautiful Sunday in MN. with a blower I can't start.

Help!

Bought new Stihl Blower from authorized dealer..took home and used for approx. 15 minutes. Now it positively will not start. Took back to dealer who cannot get it to start and refuses to replace or give money back. Will have his mechanic look at it...last Stihl product for me ever

I have a br 380,no start I changed filter fuel filter,plug,coil,fuel,cleaned the screen it has spark and compresson,pops once and the cylinder has way to much fuel in it but no start?

Gas tank vent

Ive got a Stihl SR420 its got a new carb and will not start the plug fee