Stihl TS400 Won't Start

[Millwright]

Ah ha, the dreaded two stroke tool which won't start.

I rarely use this, but when I do it's exceedingly useful, but it won't start....

....narrowed it down to no spark. I've been around the houses with this one, to the extent of a new coil and a new plug and it still has no spark. I've shorted the switch out, still no spark.

What are the chances of the magneto having failed? The magnet seems pretty strong.

Any suggestions? Thanks.

 

[Burnerman]

The igniter on these is pretty strong and the magnets on the flywheel don't fail. The air gap between flywheel and igniter should be only a tiny amount, two or three sheets of paper maybe.
Only look for a spark in darkness, make sure the plug is fully earthed onto the cylinder.
Disconnect the thin black wire from the coil to rule out the cut out switch.
John

 

[Millwright]

Hello. Yes done all that, there's nothing at all! Tiny air gap, tried in pitch black, nothing.

 

[Burnerman]

The early TS 400 ignition coil had a 3 screw fixing, the later only 2.....did you replace like for like?
I’ve never known flywheel magnets to fail so I can’t think its a flywheel fault.
John

 

[lostinthelight]

Common A4 is .09mm so Johns 2 to 3 sheets are spot on
I suppose youve checked for main bearing wear and made allowances in the gap if any?

 

[Burnerman]

I'm about stumped now - unless he has had two dud igniters
I've replaced one flywheel, due to it running slack and shearing the cast-in key and had one or two issues with the stop switch but that's about it.
Replaced many a piston and barrel though due to dust ingress, even though the air filtering is pretty good....3 filters, in fact! Fairly typical for stone cutting gear.
John

 

[lostinthelight]

I wonder if the torsion spring in the plug cap is making proper contact in the lead?

 

[Burnerman]

I gather all of this is new, so all should be well.
I use a length of wire with a miniature crocodile clip on each end to earth the plug out as the HT lead isn’t often long enough to allow the plug to sit on the cylinder head.
I can’t think of anything else, especially as Millwright has tried with the cut out wire disconnected.
John

 

[Millwright]

The early TS 400 ignition coil had a 3 screw fixing, the later only 2.....did you replace like for like?
I’ve never known flywheel magnets to fail so I can’t think its a flywheel fault.
John

Yes it's the three screw fixing coil. Will have another look at this tomorrow if I can.

 

[Millwright]

Still no spark. Everything is linked out, replacement coil, old coil, nothing. As odd as this sounds, this really does only leave the flywheel.

 

[Burnerman]

I have to agree but I've never had a flywheel demagnetise.....magnets fallen out, yes but that's about it. Do the magnets attract a screwdriver readily enough?
John
P.S. you are spinning the engine over smartly of course?

 

[Millwright]

Yes, magnet attracts quite strong. I just don't see the logic in this fault.

 

[Burnerman]

Alas a genuine flywheel is around the £90 mark which makes it a hell of a gamble
You’ve tried another plug of course?
John