Stihl 038 AV not starting

[mickdundee]

Had a couple of issues with this saw. It was running fine but then suddenly started running very fast at idle. I’ve then been an idiot and incorrectly adjusting the L screw instead of the LA screw to bring it back down. This had happened a couple of times and I continued using the saw before it cut out at idle and wouldn’t start again. 
 

I’ve realised my mistake so have set the L screw back to 1 turn out. It still won’t start. Because of the fast idling thing I’ve then tried backing the LA screw out half a turn, didn’t start so tried another half a turn and still no joy. 
 

I’ve looked through other posts and tried to rule some stuff out. Air filter is clean, fuel filter looks ok. It’s a brand new spark plug. Fuel is getting into the cylinder. Looking through the exhaust port the piston looks ok although looks like there’s carbon on the crown. Drop test is fine. I don’t know where to look for fuel tank vent. It’s not the freshest fuel but I’ve been on Aspen for over 5 years because I’m an occasional user. I’d be grateful if any pointers or ideas. Thanks 

[spudulike]

OK, the fast idle is most likely to be an air leak. I have seen fast idles been caused by bits of twig and bark but on your saw, with its age, most likely air leak.

Most likely causes, split impulse line (rubber line between the bottom of the cylinder and carb) or the inlet manifold.

The impulse is relatively cheap and easy to fit, the manifold less so.

The carb settings - set the H & L screw to 1 1/4 turns out from fully in. 

The saw may have seized, air leaks do that hence why I tend to pressure and vac check all old saws I get in.

It will be worth pulling the muffler off and checking the piston unless the saw has loads of compression on pulling it over. You can also get site of the cylinder bore through the spark plug hole, something that makes a quick check much easier.

Good luck, ask if you need any further assistance.

[mickdundee]

21 minutes ago, spudulike said:

OK, the fast idle is most likely to be an air leak. I have seen fast idles been caused by bits of twig and bark but on your saw, with its age, most likely air leak.

Most likely causes, split impulse line (rubber line between the bottom of the cylinder and carb) or the inlet manifold.

The impulse is relatively cheap and easy to fit, the manifold less so.

The carb settings - set the H & L screw to 1 1/4 turns out from fully in. 

The saw may have seized, air leaks do that hence why I tend to pressure and vac check all old saws I get in.

It will be worth pulling the muffler off and checking the piston unless the saw has loads of compression on pulling it over. You can also get site of the cylinder bore through the spark plug hole, something that makes a quick check much easier.

Good luck, ask if you need any further assistance.

Thanks spud. I’ll try and get the impulse line off tomorrow. I’ve had the muffler off and the piston looks ok scoring wise, but has carbon on the crown. It’s free to move though but feels like plenty of compression on the pull cord. If it’s the intake manifold would that be a gasket to replace or worse?

[spudulike]

OK, sounds like the piston has survived which is good. An idle that unexpectedly increases is a warning sign to stop and get it checked out by someone that knows what they are doing. 

The manifold is the rubber bellows affair that joins the carb to the cylinder. On older saws they can split, often around the clamp that joins it on to the cylinder. You really need to remove the carb, muffler and cylinder to get to it for changing.

I would check or change the impulse line first - they often get pulled off the connector just under the cylinder base especially if the bar gets compressed in a cut needing a bit of pulling to get it out. I did three 026s in three days like that! Forceps make a good tool for refitting them.

[Stubby]

10 minutes ago, spudulike said:

 Forceps make a good tool for refitting them.

Locking forceps make a good tool for skinning dog fish but that's another thread 🙂

[spudulike]

1 minute ago, Stubby said:

Locking forceps make a good tool for skinning dog fish but that's another thread 🙂

Funny that, mine came from my fishing kit, used as disgorgers.

[mickdundee]

So going back to the saw with an idea of what I was looking for it looks like not only has the impulse line split but I think a section is missing. The end of it I can see is jagged and has no chance of reaching the bare nipple at the bottom of the cylinder. It looks like a total pain in the behind to do so I’ll take it to the local shop maybe tomorrow and see if they’ll price to replace it. Thank you for the help

[spudulike]

No worries, it shouldn't take too long or be that difficult to do.

[mickdundee]

On 11/01/2022 at 21:54, spudulike said:

No worries, it shouldn't take too long or be that difficult to do.

Hi spud, the impulse line has been repaired but still not starting. The workshop has diagnosed the ignition coil and quoted over £100 for the part plus half hour labour. I’ve looked on eBay and there’s coils for less than £20. How difficult is the job? Is it worth taking a chance with a cheapo part? Thanks 

[Stubby]

4 hours ago, mickdundee said:

Hi spud, the impulse line has been repaired but still not starting. The workshop has diagnosed the ignition coil and quoted over £100 for the part plus half hour labour. I’ve looked on eBay and there’s coils for less than £20. How difficult is the job? Is it worth taking a chance with a cheapo part? Thanks 

Its not difficult to swap over but making sure you have the right one will be the thing with aftermarket stuff . Some may look the same but have different advance or rev limit etc etc .

Edited January 17, 2022 by Stubby