Stihl 031 AV issue

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.

 

huskihl
BuckthornBonnie

 

Not me. Never had my hands on one so I’m not familiar

 

More like a bad spark plug, wire, or coil

 

I'll try a working plug tomorrow. It would surprise me to be ignition as it idles fine. It just seems to need more fuel. Everytime I've had a coil issue it wouldn't idle or even run.

 

MasterMech

 

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.

 

Swap coils and ignition from a good runner.

 

This thing doesn't have some weird CV type carb on it, does it?
When you pull the throttle, you can actually see the butterfly open up, and it just sits there idling, with no change? If so, I don't see how that's even possible...
Just curious, have you done a P/V test on it?

 

No, it an old school simple butterfly. I swapped another from a running saw and it was the same. Installed the carb on the runner and it ran as well. You can see everything working fine, linkage/butterfly wise.

What's a P/V test?

 

Planning on iginition searching as suggested above after lunch.

 

Pressure vacuum test...

 

I don't know how and don't have something to do that as far as I know. LOL

 

Lol. He had or is having a sale on echo fuel line. I had me nephew check prices through his business, cheaper through taryl. So I bought two 25' rolls. One of 3/26 id and the other 15/64ths.

 

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.

 

I had bought 3 solid state coils for the 3 I fixed as they wouldn't even idle. This last one did idle so I made the mistake of thinking it was Okay. It wasn't. Never had one idle great and not rev up because of a coil or condensor. Can't say that anymore. LOL

 

Nice! That was the only saw my Dad had. Still running today. My brother has it.

 

Not to switch the subject but how’s the wood pile? If I remember correctly you had an outdoor woodstove ( possibly a Central Boiler?) & a huge surplus of cut/split firewood.