Stihl 031 AV issues

[Kevin in Ohio]

An older family friend gifted me 4 complete o31 and parts from about 3 others. He knew I tinkered with saws and he gave up on them. Told me to fix and sell as he just wanted them gone. All have nice compression and the ignition was the main culprit on them so I replace with solid state coils. he said he had spark but the wouldn't fire. I run into the weak spark thing before.

3 run fine now but one has me stumped and asking those who might know to give some tips. It starts and idles but when you hit the throttle, it just idles like the linkage isn't hooked up. It is attached. Every once in a while it will rev just less than a second then go back to idle.

I thought, Okay, carb issue. I took a carb off a runner and put it on the trouble saw and it acts exactly the same. Put the carb from the bad running saw on the runner and it runs that saw fine.

After coming in the house for the night thinking it over, could it be a restricted fuel line? Not to experienced with bad impulse lines but is that what it acts like? Bad case? I put fresh fuel in it at the start and it's idled enough to run a 1/4 tank through it. LOL

Thanks for any insight.

 

[singinwoodwackr]

Fuel starved Or plugged exhaust screen.
old fuel lines can collapse when you hit the trigger but saw will idle fine.
if a surge occurs during idle, most likely air leak.

 

[Kevin in Ohio]

Fuel starved Or plugged exhaust screen.
old fuel lines can collapse when you hit the trigger but saw will idle fine.
if a surge occurs during idle, most likely air leak.

Changed the plug from a runner and no change. Did have a SA screen on it but perfectly clean. Tore it down more and puled the muffler off and it to has no restriction. Piston looks good too with no carbon buildup in port. Pulled the fuel filter, line and outlet all out of the tank. Line has no cracks and flexibe as it should be. Sucked/blew through filter and tank plastic 90 and they are unrestricted as well. Hose going down to carb looks good, is clear and will hold a vacuum. Put it all back together and still the same. I did pay close attention to hose routing and no pinching or binding. There is still NO idle increase when trigger is pulled.

I would think if a hose was collasping you would have some increase until it got starved correct? This one does have original points/condenser as it fired when I tested it. That is what I'm leaning towards now but never seen these symptoms happen to make that the issue.

 

[singinwoodwackr]

I have one in a box to build...always looking at threads on the 031 to learn about issues that might come up. Mine is the older points style ignition as well.

I remember following your splitter build so this should be easy for you, in comparison, lol

 

[singinwoodwackr]

Swap ignition from a runner?

We're all jealous you got so many 031s

 

[Kevin in Ohio]

Swap ignition from a runner?

We're all jealous you got so many 031s

That is next on the list. Once I get them running good and cleaned up I will sell them. I do have at least 2 saws worth of various parts as well so if you need anything, let me know.

 

[Kevin in Ohio]

Switched out the coil and condensor and it solved the issue. That saw has 120 pounds of compression so it runs really good. Cleaned them all up and had enough time to put one bar on, sharpen the chain and tune. Cuts great. Hopefully get the rest of them finished tomorrow. Thanks for the help and suggestions. Never ran into that before but now I know.

 

[stihltech]

Sounded like the classic points and condenser issue. In the early 80s when there were many of them being used, pretty common.
Think I still have the dial indicator and powered test light to time the points.

 

[Kevin in Ohio]

Sounded like the classic points and condenser issue. In the early 80s when there were many of them being used, pretty common.
Think I still have the dial indicator and powered test light to time the points.

Since you are familiar with these, how about doing a run down on how to bench test both the condensers and coils? Would be helpful for those of us out there that are not in the know on these. We could toss the bad stuff and not have to guess that way.

 

[Vintage Engine Repairs]

Hope it helps:

 

[Kevin in Ohio]

Hope it helps:

Thank you!

 

[Kevin in Ohio]

Got all the non runners and basket cases done now and that's a good feeling. Had a little 009L and and 026 and finished that this morning. Coil on the 009 and crank seals and fuel line on the 026.

 

[Lightning Performance]

Old school fleet when your 026 is the new kid on the block.

 

[Kevin in Ohio]

Old school fleet when your 026 is the new kid on the block.

I'll be selling those. These are the ones I keep. Normal 3 work saws are a 192C, 028 Wood Boss and a MS660 Magnum.

 

[Lightning Performance]

I'll be selling those. These are the ones I keep. Normal 3 work saws are a 192C, 028 and a 660 Magnum.

I keep my 59cc and anything 92 and up for work tools. 200Ts only for climbing. 034/360 step in next up top. Need to run my Makitas more for bucking. 260 is house plant now. The Kitas are smooth and long with big tanks. The old pp455 bow might get the nod again soon. She loves bucking in the cold but the AV ain't the best. Feels like one of my 066/660 in my left handle. Been using the little junk box 435 lately doing small dry firewood logs for transport home. 12" and under barkless mostly. Smooth as butter. The whole 41mm bore in the beast