5100 idle?

[sevensandeights]

I just looked at the parts diagram and now I'm not sure if I have the 185-131-020 insert ring. I just realized it is inside of the green boot.

Also would like to add that my saw seems to lack power of late. Doesn't necessarily bog in the cut but it is just slower overall and bucking an 18" round takes several seconds longer that it used to. This happened about the same time that the racing idle started to occur.

 

[sevensandeights]

Adding a picture if it helps:

 

[sevensandeights]

So I tore into this thing today. Cleaned the carb as best I could. Confirmed that I do have the metal insert inside the green boot on the carb side. I also pulled the muffler and looked at the cylinder. Not sure what "normal" is. It didn't look awful but certainly wasn't pristine.

Trimmed the limiter caps and re-tuned. Saw is a little better but idle still wants to race when hot. Idle screw as minimal adjustability. You can turn it in to a point that the idle will speed up. However, once you turn it out to the point that the idle starts to come back down you can then turn it out another 3+ full turns with no effect.

Lastly. I sprayed some starting fluid on either side of the carb by the throttle shaft and the RPMs dropped consistently. I covered the air filter with paper shield while doing this. I think I read somewhere about someone having an air leak at the throttle shaft. Will a carb rebuild kit fix this?

 

[Vintage Engine Repairs]

So I tore into this thing today. Cleaned the carb as best I could. Confirmed that I do have the metal insert inside the green boot on the carb side. I also pulled the muffler and looked at the cylinder. Not sure what "normal" is. It didn't look awful but certainly wasn't pristine.

Trimmed the limiter caps and re-tuned. Saw is a little better but idle still wants to race when hot. Idle screw as minimal adjustability. You can turn it in to a point that the idle will speed up. However, once you turn it out to the point that the idle starts to come back down you can then turn it out another 3+ full turns with no effect.

Lastly. I sprayed some starting fluid on either side of the carb by the throttle shaft and the RPMs dropped consistently. I covered the air filter with paper shield while doing this. I think I read somewhere about someone having an air leak at the throttle shaft. Will a carb rebuild kit fix this?

Have you done a pressure and vacuum test and can confirm it holds?

 

[sevensandeights]

Have you done a pressure and vacuum test and can confirm it holds?

Unfortunately I don't have any of the tools to do that.

 

[Vintage Engine Repairs]

Unfortunately I don't have any of the tools to do that.

I’d say it’s leaking somewhere. I don’t think the carb, if OEM with new gaskits and diaphragms and was cleaned out is your issue. Grab a cheapie vac and pressure tester on eBay. If you ever intend on doing anything to a saw it’s the first tool to get.

 

[sevensandeights]

I think you are probably right based on what I read. Wonder why it started to leak after 11 years of trouble free service?

 

[Vintage Engine Repairs]

I think you are probably right based on what I read. Wonder why it started to leak after 11 years of trouble free service?

As I understand it (But I’m fairly new here too) a leak at the seals can sometimes decline gradually, it’s quite possible you have had a leak for a while and now it’s finally gotten to the point where it’s now showing itself. The 111cc 076 I brought is 15 years old. Tuned 1&1 by a stihl mechanic and sounded nice to me too, no lean signs, but for peace of mind I did a pressure and vac test and it has a leak. Quite a big one too.
Honestly, for 30 USD a pressure and vac tester is the best investment you’ll make. That and maybe a tach.

Worth noting - something else I was taught, a slight leak at the seals, that can be tuned out, is still likely to cause issues.

Where it sucks air at the seal, it will reduce lubrication at the bearing as it passes. Therefore even if you tune it out, you will increase the chances of bearing failure. That advice was also from my local stihl mechanic.

here is that 076 in question tuned 1&1, sounds just fine, yet the leak was very apparent when I tested it -