STIHL MS 192 tank venting issues

[Chipper461]

Hey guys, I'm new to the forum, I really appreciate all the help you guys provide and I spend a lot of time browsing your site for answers to questions and finding new tips and tricks. Anyways I have an MS 192 TC that I just rebuilt due to bad crank seals. The saw got new crank seals and a fresh piston and rings. The saw starts up and purrs like a kitten , but I cannot seem to solve my fuel tank venting issues. On a side note the fresh engine passes both vac and pressure test with no issues. The fuel tank also holds pressure nicely with the vent line plugged. I have tried applying vacuum to the vent line and it dropped slower than I liked so I installed a brand new fuel tank vent and it improved the response of the vacuum dropping in the tank, but this saw is still not venting (at least I think that's the issue) properly. It will start up and run great for probably 30-40 seconds and then bog down and only want to idle. I can turn the saw and crack the cap and its runs like a champ for another 30 seconds or so. Any ideas? Thanks!

 

[HarleyT]

See if your fuel line feels soft or gummy. It could be collapsing or kinking.

 

[Chipper461]

Could the impulse line be collapsing possibly as well? These saws do not use a ribbed style impulse line like most saws.

 

[Chipper461]

Well guys I think I finally got it figured out! It was kind of a tricky one. After pressure and vac testing the fuel system with zero leaks I started thinking more and more about the impulse line. I know there is a spring inside the tube so that it can bend without collapsing. It is pretty difficult to see the impulse line, let alone work on it, but I tore into the saw a bit and noticed sitting flat on the bench it had a slight kink where it turned 90 degrees to hook up to the rear of the airbox assembly. I started flexing the handle in the AV mounts and noticed it could kink and unkink. I removed the impulse line and realized the spring had worked its way down the line past the bend, allowing the line to kink/collapse in certain positions. This now explains while running and bogging when I turned the saw on its side or held at 45 degrees to crack the fuel cap (thinking it was the tank building a vacuum) that the saw would run better due to the weight of the saw flexing the AV mounts and "unkinking" the impulse line allowing it to run like a raped ape. I would then return to a cut and put downward pressure on the handle and flexing the AV mounts down which would then put the impulse line in a bind again. After pulling the spring all the way up so it is routed in the bent portion of the impulse line, the saw appears to run as it should! That issue did a good job of masking itself! Thanks for the help!

 

[Kaimana]

If your problem is simply a tank vent on an MS 192 TC clogged from the outside with sawdust/grunge, you can blow it off/our from the outside with compressed air without taking the saw apart or even taking the air cleaner cover off. Just direct the compressed air nozzle up under the handle on the left hand side, forward of the choke, in the crack where the handle meets the tank assembly below. If you look in here with a bright light, you can see the top of the vent; it's got a bunch of little holes in it, and if your light is bright enough, you can see the crud sitting on top of the little holes. Swish the air around from side to side in this area until the crud that was on the holes is gone, and you'll be good to go, IF your problem was a clogged vent..