Stihl BR550 blower no spark

[glentre]

New to the forum......hope someone reads this and helps with a solution.

While operating with my 6 yr old Stihl BR550 backpack blower, the motor suddenly stopped. There was no sputtering or coughing so I suspected an electrical rather than a carburetion problem. I removed the plug and grounded it out on the head but got no spark. Suspecting a bad plug, I used a spark tester inserted in the plug boot and grounded out on the head...still no spark. I removed the kill switch connection and cranked it using an electric drill to get up some speed with both the plug and tester...no spark with either. The gap between the flywheel and coil was 0.010". I cleaned off a little surface rust on the magnets and coil contacts but still no spark. The magnets were not discolored or damaged and both had strong magnetic pull.

After these tests, I felt the coil was bad. Neither of my local Stihl dealers had a coil in stock so I went on line and found a bunch of cheap Chinese coils with poor user reviews so I opted for a more expensive OEM model.

I mounted the coil when it arrived, making sure the insulating washers were installed properly between the new coil and head and the gap set correctly. The specs call for a gap between 0.006" and 0.012". I set it at 0.009" and the plug at 0.028". Cranked it up again using the drill and still no spark.

I removed the kill switch connector from the coil and again cranked it up...no spark. I ohm tested the ground wire and kill wire for continuity of the wires to the handle switch and found no breaks or shorts.

Please, can anybody help me with this no-spark problem? Unless the old coil and the new one are both bad, I can't think of anything else to do to get this blower firing.

Thanks for the help anyone can give me.

Glen

 

[upupandaway]

Try actually firing it up after pouring some gas into the cylinder.
I say this because with my BR600 I don't see any spark, tester or not yet it ran(i was testing hard to start which was from a bad plug).

 

[bertsmobile1]

Blowers spin at silly speeds
The spark from a magneto is speed dependent so at cranking speeds can be very hard to detect .
Spinning with a drill is not as fast as one would think .
To test I mount these things on the lathe and have them spinning around 4000 rpm and use a variable gap tester to check the strength of the spark.
A lot of stuffing around.
For general use I have the red flashing spark testers because the 3 point gap or white globe testers are impossible to see on hand held engines .

 

[Fish]

A drill doesn't spin it fast enough with these newer coils.

 

[glentre]

Wow! I'm really surprised that a drill is not fast enough to produce a spark. Does this mean pulling the starter cord produces a faster speed than the drill can? Thank you all for replying so quickly. Do you feel lack of start impulse speed is the reason I have no spark? Anything else I might have done incorrectly? Should I disconnect the kill wire from the coil, install the shroud and pull start mechanism and give it another try at starting by pulling the rope? Disconnecting the kill wire should take the handle mechanism out of the equation in case there is something wrong in the handle, shouldn't it?

Glen

 

[bertsmobile1]

In a workshop pulling the wire off the magneto is SOP for diagnosing .
Another trick is to ground the plug lead directly to the block and see is you get a spark.
Weak magnets will give a spark with no pug resistance but will not spark through a plug
And the exact right plug grade & gap is very important.
There were a pile of lightning flywheels around a while back where the magnets were just under spec
So it fired outside the cylinder but not under cylinder pressure.

 

[glentre]

This morning, I tried the old plug using high speed on the drill with the plug resting against the head. At very high drill speed, there was a weak spark at the plug. So then I bought a new plug and tested it the same way after setting the gap to 0.028". With high speed on the drill and the plug against the head, I could not get a spark. I then replaced the plug with a 3/8 socket extension and held it close to the head at high speed and got a good spark. So, at least I know the coil is capable of generating a spark, although a weak one that apparently can't pass through a plug. Any suggestions on what I should do now would be appreciated. I have the shroud and pull start off the blower plus the handle is apart. With still no good spark at the plug, I am reluctant to put everything back together if I know the spark is not strong enough to fire up the motor.

Glen

 

[Fish]

Pull the muffler and look at the piston condition.

 

[bertsmobile1]

That says weak magnets in the flywheel
Try setting the coil closer to the flywheel and see what happens.

 

[glentre]

Thanks for the suggestion. I'll reset the coil closer to the magnets in the morning and give it a try. Should have thought of that. Can magnets go bad all a sudden and the engine just stops when it's been running fine for the previous half hour and then not be able to generate a spark?

Glen