Question about a Mac 10

[NewToStihl]

Okay, you McCulloch guys please forgive me for my complete lack of knowledge of the brand or any model they've every made.

I coworker of mine asked me today if I knew what might be wrong with his "really old Mac 10" chainsaw. He said it starts and runs well, but dies when tilted on the side. We only had a moment to discuss it, so that's all I was able to get out of him. Next time I run into him I'm going to see if I can get my hands on the saw to properly diagnose it, but I was curious what you guys thought. My first instinct with that symptom is a bad oil seal, but I know zero about those saws so for all I know it could be a host of issues...

Any suggestions would be appreciated.

 

[machinisttx]

oil seal most likely

 

[motorman1]

oil seal most likely

Oil seal, or could be fuel line inside tank is "soft" and collapsing.

 

[NewToStihl]

Thanks guys. The fuel line would be easy to check & replace if necessary, but if it is an oil seal issue are replacements available for that model (due to age) and how challenging are they to replace? Is it pretty much the same as it would be with most older mag case Stihls? I've replaced seals on those and have a seal puller.

 

[Duke Thieroff]

Let's go for the simple thing first...bad seals cause an air leak. Air leaks cause lean conditions, lean conditions cause the saw to rev up.

If the saw sounds like it is getting loaded up when on it's side at idle I would suggest L screw carburetor adjustment first. Sounds like it is too rich.


When turned on its side at idle with low crankcase pressure it will make excess fuel pool up on one side of the crankcase and up one side of the transfer ports. Effectively overloading the top end with fuel and stalling the motor out.

I'd suggest a carb cleaning and inspection of diaphragms, metering lever, needle, spring, welch plugs, and an adjustment of the carburetor before you pin an oil seal as the issue.

 

[rmh3481]

If Duke doesnt have your seals, these guys should;
http://www.fayettevilleequipment.com/

 

[roosterhog]

I'm like Duke. I think it might be the low speed screw on the carb. I've straightened several of mine like that out in the past. Make sure the saw is good and warm before you try to adjust. Just cranking them up and turning screws before they get warmed up is a bad deal. My experience has been that it will likely only take like 1/8 of a turn to correct the shutting off when tilting problem that you describe.

 

[NewToStihl]

Thanks for the suggestions. I talked to the guy yesterday and he's going to bring the saw in for me, so it'll be interesting to get to look at it and run it myself. I'll report back on what I find.