Any Stihl chainsaw experts here?

[minimutly]

Thought it was time I sorted this out.

It's an ebay bought chainsaw, starts but won't run, I put it to one side because it looked horendous to strip, turns out it was..
Anyway, started out by inserting a neon in the plug to check it wasn't electrical - all ok there.
So drained the fuel and chipped away at it..

The only the questionable thing I found was this vent tube, with two grub screw type things restricting flow. Both the fuel and impulse ? tubes are good, the Walbro carb looked ok, but I blew it out anyway. So now I rebuilt it and hope for the best.

 

[reb78]

Did you look at the condition of the piston?

 

[minimutly]

Did you look at the condition of the piston?

It has excellent compression, and yes, from looking through the exhaust port it's like new. I removed the silencer, filled it with carb cleaner and torched it, came up like new.

 

[minimutly]

The clutch may be knacked though?

 

[minimutly]

 

[Barking Mat]

Carb ?

Fuel in tank filter ?

 

[minimutly]

Anything else I should check before rebuilding it? I'm disappointed I can't see a reason for the failure to keep running - it does run a little weak when it does, then stops suddenly. Maybe I'll turn the mixture screws out a turn when I try it.

 

[minimutly]

Carb ?

Fuel in tank filter ?

I checked and washed the tank out, looks spotless even if it was "just ok" before. The carb looked ok too...

 

[Mike Pinches]

It's probably worth cleaning the carb out properly anyway, the passageways are tiny and block easily. Also fit new diaphragms after cleaning, they are cheap enough and carb problems are a very common reason for saws not running.

 

[Barking Mat]

In my experience chainsaws are a PITA, but that's me, great when they work, but when they don't ... Same with all two stroke stuff.

 

[addjunkie]

In my experience chainsaws are a PITA, but that's me, great when they work, but when they don't ... Same with all two stroke stuff.

Id agree unless used very regularly!

 

[angellonewolf]

As you say you know it runs so carb clean new gaskets and so w times they needs a sonic clean a few times

If that don't work then new carb


But yes an adjustment on the carb is some times all they need but if you adjust it wrong it starves of fuel hence no Oil and buggers up the pistion etc watcha few vids at least before doing adjustments and have a rpm tool as well unless you have done meny

 

[Smallfry]

Does the fuel pickup filter look anything other than white ? If not, fit a replacement. That would be my first port of call. You have already taken the silencer off and looked at the piston and ring/s, and the opposite side of the bore for scoring, so that should be OK

How long does it run for before it stops ?

If it runs long enough to get something like hot, when it stops, test for spark. If no spark, possibly the ignition unit. If there is spark, try a new spark plug.

If not that, move onto fuel system, as already said, tank vent may not be working, air leaks in pipes, then clean and rebuild carb with new diaphragms.

 

[JOEPRO]

Thought it was time I sorted this out.View attachment 476198
It's an ebay bought chainsaw, starts but won't run, I put it to one side because it looked horendous to strip, turns out it was..
Anyway, started out by inserting a neon in the plug to check it wasn't electrical - all ok there.
So drained the fuel and chipped away at it..View attachment 476199
The only the questionable thing I found was this vent tube, with two grub screw type things restricting flow. Both the fuel and impulse ? tubes are good, the Walbro carb looked ok, but I blew it out anyway. So now I rebuilt it and hope for the best.

A hose with grub screws inside is an old school way of a tank vent. That's how it was done. So that's a vent tube.

 

[Kram]

Does it have a primer bulb, if so does it prime? The fact you said it starts, tells me thats not an issue.

However, I've seen a few carbs that look perfect inside but wont run or wont prime. The most recent, I discovered the throttle butterfly accelerator pump piston, and it appears common for the O ring seals to fail. When this happens, air leaks into the carb and prevents fuel flowing to it.
This issue is something I will make a habbit of checking, particually as I have a pack of 24 spare 3mm O rings to use up...


Also while you said it sparks, it could be the flywheel lost its key or out of alignment and giving bad timing.

Crank seals?

 

[minimutly]

No bulb, not sure how you are meant to prime it
I checked the spark before stripping it, it's good.
I wondered about crank seals from the beginning - no idea how to check them though?
It runs for 30 seconds or so, then just dies

 

[Smallfry]

No bulb, not sure how you are meant to prime it
I checked the spark before stripping it, it's good.
I wondered about crank seals from the beginning - no idea how to check them though?
It runs for 30 seconds or so, then just dies

On the strength of that, I would say spark plug, ignition unit, tank filter, tank breather, before going any further.

 

[Kram]

30 seconds is reasonable. What happens if you slowely give it little pulses of throttle? Sometimes my 020T needs that to get some heat in, then it starts to run normaly. Without doing the throttle it will run for ten secs and die repeatedly and never get enough heat.

If it doesnt have one, then its self priming - actually they are purge bulbs as they push air out, causing a vacuum and sucking fuel through carb. I'm not yet sure how they work without it- I know the fuel diaphram and reed valves act as a fuel pump and it may be that these saws a have enough suction, to not need it..?

I think for seals you need a vacuum/pressure tester.

 

[JOEPRO]

When you rebuilt the carb did you follow all crucial steps

Ultrasonic cleaner with proper solution
Carb cleaner to blow through all ports and verify clear
New gasket and needle kit

If any step is missing, that's your problem. Stick with the genuine carb and avoid aftermarket, they are all terrible bar none.

 

[reb78]

I just replaced the seals on my 044 as I couldn't easily pressure test. Mine was fooked though as the piston was heavily scored, rings welded in their grooves and a lot of piston was stuck to the cylinder. I saved the cylinder and put a new piston in. It works a dream now, very powerful.

I have a thread on it on here somewhere I think.

Yours doesn't sound anywhere near as bad so if you think spark is ok, I'd be concentrating on fuel as above.