Hi everyone! I just want to start out by saying that I've learned a lot from this forum over the years, enough so that I've been able to find the answers I needed without ever registering. So, thanks for making this valuable resource available. Now, however, I've encountered issues with a saw that has me stumped enough I think I need assistance with my specific problem.
I've got a Sthil 028 AV Super Wood Boss that I inherited from my aunt and uncle. They were known for buying high quality equipment and lightly using it, and I suspect this saw fits in that category. I'm guessing it had more years where it never was started than ones where it did. I've had it for the last few years, tinkering with it some and actually using it some a couple years ago, but recently it's started giving me major trouble. Currently it will start and idle fine, but the instant that I try to cut with it, it bogs back to idle. It will restart easily, either cold or hot.
Since I'd done carb work on this saw once before (it needed a new diaphragm when I took it out of storage), I just put a new carb on it to test. It made no difference. I did adjust it before trying to cut with it.
I checked the compression with an automotive gauge and it was about 90 psi on the first pull, going up to about 150 after a couple more. From what I've read on here, I think that's fine. It certainly feels like it has plenty of resistance when I pull the starter cord.
From there I read that it could be sucking the choke plate closed, so I removed it after the saw was warm. That made no difference. I also removed the grub screw from the fuel vent line to see if that made a difference; it didn't. The fuel filter is new and doesn't act plugged. So I tried removing the entire air filter to see if it was clogged, even though it seemed to be clean after I blew the chips off it. Even with a warm saw I had a heck of a time getting it to start and it seemed to be blowing a fair bit of fuel mist back out of the carburetor. When I did get it to run, it still bogged down the same as it has been.
At that point, I did some more reading on here and saw where someone suggested that points issues on an older saw could cause it to spit fuel like that. This saw has an electronic ignition, but I replaced the coil anyway, and it made no difference. I replaced the spark plug at the same time, but the old one looked fine and was a tan / brown color on the electrode that seemed normal to me.
Then I read that it's important to do vacuum and pressure checks on the crankcase. I only have a MityVac vacuum tester now (pressure tester is on the way, due here early next week), but I made block off seals for behind the carb and the muffler and tested it for vacuum through the compression tester hose. I did remove the check valve in the hose after confirming it wouldn't work under vacuum with it in there. I took it to 15 inches of mercury and it took about 90 seconds to lose 1 inch of mercury. I know that's not zero, but I'm not confident that I might not be losing some due to my worn out MityVac tester or the hoses. Is that enough to cause the saw to instantly bog down if it was all from the saw and not the tester?
Is there anything else that I'm missing that I should be looking at or testing? I'm normally pretty good on 4 stroke engines, but I've never gotten along well with 2 strokes other than my little workhorse MS180 (side note - that little 2013 vintage MS180 has been one of the best investments in tools that I've ever made!). I'm hoping that I'm missing something obvious that you kind folks can guide me towards, as I'd really like to get this saw back to doing what I know it should be capable of. I've got a dead ash tree behind the house that needs felled that is just too big to tackle with a 14 inch bar MS180. Thanks in advance for any assistance you can give!
I've got a Sthil 028 AV Super Wood Boss that I inherited from my aunt and uncle. They were known for buying high quality equipment and lightly using it, and I suspect this saw fits in that category. I'm guessing it had more years where it never was started than ones where it did. I've had it for the last few years, tinkering with it some and actually using it some a couple years ago, but recently it's started giving me major trouble. Currently it will start and idle fine, but the instant that I try to cut with it, it bogs back to idle. It will restart easily, either cold or hot.
Since I'd done carb work on this saw once before (it needed a new diaphragm when I took it out of storage), I just put a new carb on it to test. It made no difference. I did adjust it before trying to cut with it.
I checked the compression with an automotive gauge and it was about 90 psi on the first pull, going up to about 150 after a couple more. From what I've read on here, I think that's fine. It certainly feels like it has plenty of resistance when I pull the starter cord.
From there I read that it could be sucking the choke plate closed, so I removed it after the saw was warm. That made no difference. I also removed the grub screw from the fuel vent line to see if that made a difference; it didn't. The fuel filter is new and doesn't act plugged. So I tried removing the entire air filter to see if it was clogged, even though it seemed to be clean after I blew the chips off it. Even with a warm saw I had a heck of a time getting it to start and it seemed to be blowing a fair bit of fuel mist back out of the carburetor. When I did get it to run, it still bogged down the same as it has been.
At that point, I did some more reading on here and saw where someone suggested that points issues on an older saw could cause it to spit fuel like that. This saw has an electronic ignition, but I replaced the coil anyway, and it made no difference. I replaced the spark plug at the same time, but the old one looked fine and was a tan / brown color on the electrode that seemed normal to me.
Then I read that it's important to do vacuum and pressure checks on the crankcase. I only have a MityVac vacuum tester now (pressure tester is on the way, due here early next week), but I made block off seals for behind the carb and the muffler and tested it for vacuum through the compression tester hose. I did remove the check valve in the hose after confirming it wouldn't work under vacuum with it in there. I took it to 15 inches of mercury and it took about 90 seconds to lose 1 inch of mercury. I know that's not zero, but I'm not confident that I might not be losing some due to my worn out MityVac tester or the hoses. Is that enough to cause the saw to instantly bog down if it was all from the saw and not the tester?
Is there anything else that I'm missing that I should be looking at or testing? I'm normally pretty good on 4 stroke engines, but I've never gotten along well with 2 strokes other than my little workhorse MS180 (side note - that little 2013 vintage MS180 has been one of the best investments in tools that I've ever made!). I'm hoping that I'm missing something obvious that you kind folks can guide me towards, as I'd really like to get this saw back to doing what I know it should be capable of. I've got a dead ash tree behind the house that needs felled that is just too big to tackle with a 14 inch bar MS180. Thanks in advance for any assistance you can give!
