MS270 won't quit

[jeff_t]

Why won't it shut off? I have the carb and top cover off, and the wires appear to be ok, though the green wire was kinda squished up against the coil.

I'm sure this isn't uncommon, but I couldn't find anything with a search.

 

[Danno77]

Dunno what's under the cover on those, but ive got my money on the choke switch that grounds out in the off position. Some have a little tab that gets bent the wrong way.

 

[jeff_t]

That looks too simple to malfunction. Appears to be making good contact.

 

[Danno77]

That green wire prob runs back to the coil area and if it came loose there it could be the prob as well. Problem is you have to take it apart even more to get there!

 

[jeff_t]

I have the top plastic of the saw off, and everything looks good to the coil and back. I suppose a continuity check would be in order.

 

[Danno77]

Yup.

 

[StihlHead]

The kill switch on any newer Stihl saw (270 included) grounds the coil out in the up position. There are metal tabs on the choke lever mechanism that make contact when the choke lever is flipped all the way up. In that position, the black coil wire the a green ground wire are connected, and the saw shuts off w/o a spark. Usually the metal tabs break, move or get loose from the wire connected to them, or the choke lever tabs break and contact is not made. 99% of the time its on the choke lever side and not the wires on the coil side, as those are stationary and bolted down with torx bolts and they do not move. Sometimes a wire gets cut, but that is very rare.

The 260 is notorious for this happening as the lever tabs get loose over time. Generally I bend the metal tabs so that they make contact, and that is all they need. It is also common that the metal tabs break off, or they move out of position and they have to be re-set in place. Sometimes a fussy one has to have the metal contact removed and the wire connected to it re-crimped and the tabs/wire ends re-set in place. Sometimes a choke lever plastic tab breaks and has to be replaced, or repaired with super-glue. Pull the AF cover off and maybe the air filter to get at the kill switch tabs. Thumb the saw into the off position and see if the metal coil tab is making contact with the ground wire end or tab. If not, adjust it so that it does, or find out what is broken that is keeping that from happening. That's all it usually takes.

If it still does not work... all Stihls are the same on the coil side as well. Pull the torx bolts holding the starter assembly in place and pull the starter off. On the right lower side the coil will be bolted into place next to the flywheel. It is held in place by torx bolts. Make sure the bolts are tight. The black wire will come from the coil/ignition, and the ground wire will be connected to a metal ring that is bolted to the coil housing. There is not much else to do or to replace in there. Make sure the wires are connected and not cut anyplace, and that is about it. There are different wiring harnesses on different model Stihl saws, but all have a black wire running to the kill switch, and all have a green wire from ground to the other side of that switch. They run through a grommit into the air intake area near the carb where the choke lever is.

 

[Danno77]

Yer wordy, but that's exactly what I was thinking. The ignition kill system is pretty simple, the fix is generally easy.

 

[jeff_t]

I think I found a short in the wire where it is routed back behind the carb and up towatd the coil. I would hope it's pretty cheap, or should I try to fix it?

 

[Danno77]

That isn't too big of a deal. Cut it, strip it, twist it, tape it. Good to go for years.

 

[StihlHead]

I think I found a short in the wire where it is routed back behind the carb and up towatd the coil. I would hope it's pretty cheap, or should I try to fix it?

If its a short in the black wire, it would not run at all (coil always grounded). If it is a short in the green wire (grounded... ground), the kill switch would still work.

If it is a cut wire, you can replace them for pretty cheap, and easy to do yourself. They come in a set from Stihl, or you can get them on Ebay and the like. You can repair them with tape or heat shrink wrap too. They are usually just long enough to be routed from the coil to the kill switch though and splicing them usually makes them too short, or too tight to work right. Also the splice is a weak point in future.

 

[jeff_t]

It's not a short to ground, or even a bare wire. It's in the insulation somewhere. It was still running as I was poking around with a pencil, wiggling wires until I found a spot where it shut off consistently. I'll get a new set and do it right.

Thanks for thinking with me.

 

[StihlHead]

Wire break under the insulation... Not unheard of, but not common. You saved yourself $100 of chainsaw mechanic diddling, and a good chance of them breaking something else in the process.

$13 with shipping new/OEM 270 wiring harness:

http://www.ebay.com/itm/NOS-OEM-STI...948158577?pt=US_Chainsaws&hash=item3cc1b8e871

 

[jeff_t]

Thanks for the link. I made a bit of a lowball offer, so we'll see what happens.