Stihl 031 AV Issue - Won't Stay Running

[gvsu141]

I'm trying to sort out an issue with a 031 AV Stihl that I have. This is labeled the "electronic" version. I cannot get the saw to stay running no matter what I do. Any suggestions would be appreciated.

I have some mixed gas in a spray bottle as starter fluid. If I give it a couple sprays in the carb, it fires right up. Runs for a couple seconds then dies. Occasionally it has run for 30 seconds before dying, and sounds/revs great. However 99% of the time, it only runs for about 5 seconds. It will not run without the starter fluid, so seems to be a fuel problem.

-Compression is great. 170+ PSI If I recall.
-Rebuilt the carb with a new Oregon kit. Old metering diaphragm was cracked. Carb is spotless with all new parts. I've had this carb apart at least 3 times checking everything is good
-When I take the carb apart, there is gas in the carb.
-Adjusting L & H mix screws do not seem to help.
-Removed fuel lines, inspected and reinstalled. Fuel filter and lines are good.
-New spark plug.
-I haven't removed the pulse line, but seems to be working when pulling over without the carb
-Fresh gas (Same gas I use for the starter fluid bottle)

 

[Wright Saw]

Have you tried running it with the fuel cap loose, in case the fuel tank vent is not working?

 

[gvsu141]

Have you tried running it with the fuel cap loose, in case the fuel tank vent is not working?

Yes, thanks. Forgot to mention that. Fuel cap off does not make a difference. It needs a new fuel cap anyway since the valve was broken/removed by P.O.

 

[HarleyT]

Take your carb apart again. Remove the covers and diaphrams, also remove the needle/lever/spring, and visually insure the passage beneath is totally clear.
Also, take apart the fuel filter and see if the foam insert is OK, that is, if it is the original style.

 

[HarleyT]

Is it a Walbro or Tillotson carb?

 

[gvsu141]

Take your carb apart again. Remove the covers and diaphrams, also remove the needle/lever/spring, and visually insure the passage beneath is totally clear.
Also, take apart the fuel filter and see if the foam insert is OK, that is, if it is the original style.

As for the carb, I've had the diaphragms & needle off a couple times with no luck. The needle passage is easy to see, and is spotless. I've sprayed carb cleaner with the nozzle in all other smaller passages, and they are all clear, including the ones with the mixture screws. I've worked on a bunch of carbs in the past (mostly motorcycle) but this one has me stumped.

Fuel filter does not have a foam insert, but fine mesh screens. I've taken this out and cleaned it. I've even tried running it with the filter off to see if that would help with full tank, with no luck.

 

[gvsu141]

Is it a Walbro or Tillotson carb?

Tillotson Carb.

 

[HarleyT]

It is important to actually look through the passage, as the tiny particles from the disintegrated foam insert in the fuel filter pack and clog everywhere. Some gas may get past the blockages, but not enough to run the saw.

 

[gvsu141]

It is important to actually look through the passage, as the tiny particles from the disintegrated foam insert in the fuel filter pack and clog everywhere. Some gas may get past the blockages, but not enough to run the saw.

I can check again, but how would you look through all of the smaller passages? The main needle passage I understand, but the ones for the jets, etc are too small to see through? They seem to be flowing a lot of carb cleaner though.

Makes sense about the foam. If all else fails I suppose I could just get a used carb on eBay, but I would like to get this one going if possible.

 

[HarleyT]

When you have it apart, hold the carb up to a light.
Also put up some pics, show us the lever height before you remove it.

 

[gvsu141]

When you have it apart, hold the carb up to a light.
Also put up some pics, show us the lever height before you remove it.

Sounds good, thanks. Will not have a chance again until after the weekend. Have tried both the old lever that was in it, along with the one in the kit with no success. Haven't tried changing the height.

 

[Chainsaw Jim]

I think the problem is the crank seals. The same bad fuel that ruined the kit in the carb will aslo eat the seals. Without a good seal the motor will never be able to pull fuel from the tank. That's why it'll only pop when bottle fed.

 

[Sam R]

I'm with Jim on this one. I suspect an air leak. Bad seals or the intake boot can develop a hole too which will eliminate the ability of the saw to generate pos/neg pressure for the pump.

 

[Steve670]

Check the fuel line, the piece that goes from the tank to the carb, if it's too long it can get kinked by the air filter.

 

[burnses]

I love it when fall starts to roll around and all the old stuff comes out of the wood work for some run time...not many saws can generate the kind of mechanical frustration of a lonely old 031....no spark week spark no fuel to much fuel wont start wont rev run great long enough for ya to think ya got it fixed and it craps out.....31 is unique in a way that it has to draw the fuel up and over the top of the tank then to the carb...but if you have a vac gauge or a hand mini vac hand pump I would suggest tank the fuel line off the carb and connect your gauge remove the spark plug and pull the engine over you should see the needle pulse as the carb diaphragm tries to pump fuel that would tell ya the carb can draw fuel to it.....also remove the carb and connect your vac hose to the pulse line in the same way and pull the eng over and ck for vac pulse if so then you might assume it would run without doing a more complicated but at some point necessary pressure /vac test on crankcase to ck crank seals....ya could take off the fuel filter and connect your gauge and again pull over the engine and ck for suction pulse at that point....if no pulse could have issue with fuel hose to plastic fitting in tank at top....but when ya get it figured out you will be running it all proud that you persisted and fixed it .....then it craps out soon as the ignition heats up and loose spark so ya either fix the ignition or run it in the winter only.....get the idea! good luck...btw I have 031 and a 32 I run em sometimes!

sap can

 

[trappermike]

My bet is the impulse hose is cracked,or maybe the intake boot is cracked. Remove the tank assembly and inspect those items.

 

[raybow1]

My thoughts are in either the impulse or fuel line coming out of the tank to the carb is compromised. Track that fuel line all the way from the outside of the tank to the carb. Also pull the fuel line from the carb and see if it is pressurised and spews gas. The fact that it runs up to 30 se ones would lead me to believe maybe impulse issue and not getting crank case pressure to carb. Also, as mentioned seals. I don't think this is the issue but would have to b a massive leak in seal not to at least fire up in normal procedure. That being said, they should b changed as a normal maintenance procedure anyway.

 

[corbin nelson]

I'm trying to sort out an issue with a 031 AV Stihl that I have. This is labeled the "electronic" version. I cannot get the saw to stay running no matter what I do. Any suggestions would be appreciated.

I have some mixed gas in a spray bottle as starter fluid. If I give it a couple sprays in the carb, it fires right up. Runs for a couple seconds then dies. Occasionally it has run for 30 seconds before dying, and sounds/revs great. However 99% of the time, it only runs for about 5 seconds. It will not run without the starter fluid, so seems to be a fuel problem.

-Compression is great. 170+ PSI If I recall.
-Rebuilt the carb with a new Oregon kit. Old metering diaphragm was cracked. Carb is spotless with all new parts. I've had this carb apart at least 3 times checking everything is good
-When I take the carb apart, there is gas in the carb.
-Adjusting L & H mix screws do not seem to help.
-Removed fuel lines, inspected and reinstalled. Fuel filter and lines are good.
-New spark plug.
-I haven't removed the pulse line, but seems to be working when pulling over without the carb
-Fresh gas (Same gas I use for the starter fluid bottle)

Make sure your clutch isn't dragging