Stihl 038Av Super cuts out when hot and wont start

[Richie R]

Hi there,

 

As you can see this is my first post here so i hope you don't mind me asking for some help?

 

I purchased a Stihl 038AV Super (eBay) May 2009 for logging on the country estate where i live (lots of fallen limbs and trees)I didn't pay a lot for the saw (so i thought (£150)) and was pleased it ran properly as it had been stood in a shed, half full of fuel for a few years.

 

The first time i used it, it got a fair old session - about 3hrs cutting a 24 inch ash trunk that had been down for about 4 years - but eventually it wouldn't idle when it got hot then wouldn't start.

SIEZED!

The piston rings had melted at one side and both piston and cylinder were badly scored. My local Stihl dealer/repair center estimated a £350 repair so i took it home.

 

I purchased a repair kit (cylinder, piston, rings, gasket kit etc. £70 - eBay again) thinking i was still only in for about the standard used price for an 038 and mine would have a brand new piston and cylinder.

 

After rebuilding the engine with the new cylinder and piston kit it started after a few pulls. Great. Ran it in for 10 mins on half revs.

Now to the log in the garden - the same 24 inch ash from last year.

 

Sliced off one piece and sat the saw down ticking over to move the piece out of the way and it cut out. AARRHH. Wouldn't start.

Fired a bit on furious pulling but that's it. The saw was quite hot at this point so i was right back where i started and feared the worse.

I let it cool and it started again fine.

 

So it seems that the cutting out is directly related to getting hot.

 

I took the muffler off - no scored piston - same with the carb side so I'm crossing fingers there has been no damage but of course the problem still exists.

 

I have read through many forums, threads and posts with lots of possibilities the main being running too lean due to an air leak somewhere.

 

So after that epic description here are my questions;

 

1) When the saw is sat on the floor for a while there is oil coming underneath from somewhere. Is this likely the chain oil tank/pump?

 

2) If the crank seals have gone how can i test this without specialist equipment?

 

3) I have noticed after it has been running and i remove the fuel cap there is a pressure release. It feels like the tank is creating a vacuum, is this normal?

 

4) Could a carb kit fix lean running?

 

5) Could it be the ignition coil?

 

I am not 100% sure it is running lean as the plug doesn't look too bad. Its a brown colour on the tip and pot and silky looking.

 

Any help would be great here to keep life in the 038

 

Cheers

[rxe]

How have you tuned it? Before suspecting anything else, suspect the carb settings as these are generally mullered on every ebay saw. I haven't got the specs for an 038, but I'd suggest 2800 rpm idle and 12,000 wide open as a good starting point.

 

Which side did the piston score on: exhaust or inlet? Exhaust side indicates lean condition, inlet would suggest ingestion of crud.

 

My suggestion:

 

- strip and rebuild the carb with a new pump and gaskets

- check that the fuel line is intact, no holes, and the filter is unblocked.

- check that the impulse is intact, no holes.

- Set the carb up with a tach, if it doesn't respond properly, then suspect air leaks.

 

Is is actually running properly? Sharp chain? 3 hours for one log seems....excessive. I think I'd have a 24" log in matchsticks after 3 hours cutting.

 

To answer the specifics:

 

1) When the saw is sat on the floor for a while there is oil coming underneath from somewhere. Is this likely the chain oil tank/pump?

 

Yes. Get some newspaper to leave under it, that's what everyone else does.

 

2) If the crank seals have gone how can i test this without specialist equipment?

 

You can't. You'll need a carb adapter (not very expensive), a bung for the exhaust (make one) and a way of getting pressure and vacuum in - you can make all this, but it gets expensive. Pressure and vac test - best done at the dealer.

 

3) I have noticed after it has been running and i remove the fuel cap there is a pressure release. It feels like the tank is creating a vacuum, is this normal?

 

No. Check the air vent in the tank. Looking the IPL, it seems to be a "bolt in a bit of tube job". Does it start after equalising the pressure in the tank?

 

4) Could a carb kit fix lean running?

 

It could if the pump membrane is damaged or stiff, or the carb is full of crud.

 

5) Could it be the ignition coil?

 

Unlikely if the saw has been running well, though they are the work of the devil and do sometime cut out when hot. Suspect the carb first though.

Edited September 8, 2010 by rxe

[Tommy_B]

Stihl 038 have a very bad tendancy to take crud into the carb , clean the carb and change diagphram. There isnt a pre filter on these and frequent strip downs were common to clean the carb .