Bryan Duxbury
ArboristSite Lurker
I recently purchased a Stihl 075AV to use in an Alaskan mill. It worked when I bought it, started right up on first few pulls, though it needed a bit of tuning on the carb + idle settings to stay running after it started. I used it a few times while I was waiting for the proper bar and milling equipment to show up, and now that it's finally here I have started having a tough time.
First up, took a slab off a log no problem, so decided to go right back at it for the next slab. About 75% of the way through the saw started to sound a little off, and I was thinking maybe I ought to have put more gas in between slabs, so I stop it and set about pulling it out of the cut. That's when I noticed a suspicious piece of hardware sitting on top of the pile of sawdust... which turned out to be the saw's decompression valve! Yes, it had literally backed itself out and dropped due to vibration. I figured this was the source of at least some of the ragged performance, so I set about re-installing the valve.
Getting at the hex shank on that valve was a pain in the butt that required removing the air filter carrier to access the screws for the muffler. Once I'd figured that out and gotten the valve reinstalled, I goofed up and dropped one of the air filter carrier nuts down into the carb. Sigh. So I took out the carb, retrieved the nut, and went about putting everything back together, assuming that would be the end of it.
So I get the saw back down to my log and pick up where I left off. Now when I'm nearly done with the slab the saw really starts to underperform. Basically, as soon as the chain really starts to bite, the saw bogs down. I manage my way through the rest of the slab and then start prodding the saw to see what's going on. What seems to happen is that the saw is perfectly happy to idle, but after about 2-3 seconds of wide open throttle (even outside the cut), the saw starts to struggle and sounds like it's going to stall.
At this point I'm guessing that I messed something up with reinstalling the carburetor (hoses or something?) and decide to take it all apart and have a look. With the carburetor out, I checked the fuel pump and found a bunch of gunk in what I think was the fuel strainer, so I scraped it out; otherwise, everything looked ok. I also checked the opposite side (the metering chamber?) but everything "looked ok" and I'm not really sure what to expect in there anyway.
When I finally got everything back together, the result wasn't good. The saw still started up no problem after a few priming pulls, but now it's struggling both idling and at speed. I can't tell if I'm just super frustrated or genuinely lost here, but I would love some experienced folks to chime in with what I should investigate next.
One other thing I noticed is that the gasket between the air filter carrier and the carburetor looks like it was hand made at a later date - it's some kind of blue papery material. Not sure if this is likely to be the source of the problem, but I'd be happy to change it out if there was any chance it would improve things. What kind of material should I be sourcing to do this?
First up, took a slab off a log no problem, so decided to go right back at it for the next slab. About 75% of the way through the saw started to sound a little off, and I was thinking maybe I ought to have put more gas in between slabs, so I stop it and set about pulling it out of the cut. That's when I noticed a suspicious piece of hardware sitting on top of the pile of sawdust... which turned out to be the saw's decompression valve! Yes, it had literally backed itself out and dropped due to vibration. I figured this was the source of at least some of the ragged performance, so I set about re-installing the valve.
Getting at the hex shank on that valve was a pain in the butt that required removing the air filter carrier to access the screws for the muffler. Once I'd figured that out and gotten the valve reinstalled, I goofed up and dropped one of the air filter carrier nuts down into the carb. Sigh. So I took out the carb, retrieved the nut, and went about putting everything back together, assuming that would be the end of it.
So I get the saw back down to my log and pick up where I left off. Now when I'm nearly done with the slab the saw really starts to underperform. Basically, as soon as the chain really starts to bite, the saw bogs down. I manage my way through the rest of the slab and then start prodding the saw to see what's going on. What seems to happen is that the saw is perfectly happy to idle, but after about 2-3 seconds of wide open throttle (even outside the cut), the saw starts to struggle and sounds like it's going to stall.
At this point I'm guessing that I messed something up with reinstalling the carburetor (hoses or something?) and decide to take it all apart and have a look. With the carburetor out, I checked the fuel pump and found a bunch of gunk in what I think was the fuel strainer, so I scraped it out; otherwise, everything looked ok. I also checked the opposite side (the metering chamber?) but everything "looked ok" and I'm not really sure what to expect in there anyway.
When I finally got everything back together, the result wasn't good. The saw still started up no problem after a few priming pulls, but now it's struggling both idling and at speed. I can't tell if I'm just super frustrated or genuinely lost here, but I would love some experienced folks to chime in with what I should investigate next.
One other thing I noticed is that the gasket between the air filter carrier and the carburetor looks like it was hand made at a later date - it's some kind of blue papery material. Not sure if this is likely to be the source of the problem, but I'd be happy to change it out if there was any chance it would improve things. What kind of material should I be sourcing to do this?
