046 tank vent

[k nystrom]

First off, thank you...been lurking here for years learning how to fix my saws - invaluable stuff in these pages

So I have an 046 (newer one of 2 of these lovely beasts) which I just rebuilt the carb on. Fired him up and all was well (other than needing a bit of fine tuning), bucked up some logs for about a half hour and he stalls. So I fiddled a bit with the carb and no change. Fires up on one pull, idles fine, then as the throttle is depressed, quits. There doesn't seem to be much in the way of pissing when the fuel cap is opened, and the behavior is the same on starting.
This thing had an ancient tank vent on it (one of the grub screw tube things). I discovered that the tube was cracked, so i pulled the little white end with the screw in it off, and replaced the old tube with some fuel line, and I also replaced the orange umbrella valve.

Still the same...

Prior to rebuilding the carb, the saw would run, race and die. I pressure tested and vacuum tested it successfully with no leaks.
I just tried pulling a vacuum on the fuel line to test the vent and couldn't pull any vac at all... Is this normal behavior or should it pull some vac and just leak?

Also the IPL shows a little valve (#40) - is that part of this system or the newer mushroom looking one? Right now I have #31, 32 and 33 on it. This vent (1128 350 5802) seems to be extremely hard to find, which is why i tried to just replace the line on it...

 

[Poleman]

I would say #40 is a duck bill valve that belongs in the old system like you have.
The new system is 4, 5 & 31

Try pressurizing your fuel line instead of vacuume. Pull the line up pull the filter and pressurize to 7-10 lb and watch for a drop. Sometimes I leave fuel in the tank to spot bubbles. I’ll wiggle and lightly pull on the line to open cracks/holes. If no bubbles in tank pull the line off the carb and block with a golf tee, retest. If it holds now there’s a pressure drop in the carb. Needle not sealing, needle arm too high, leaky gaskets but that usually showed fuel seepage in the air box area.
I’m sure the vent your looking for is NLA as updates surpass the dated ones.

 

[k nystrom]

Thank you!

OK, so the saga continues... I left the saw last night, pulled it out this morning and pressurized the fuel line - no drop... I had pressure tested the carb before I put it back in after building it... I did the pop-off pressure test on (which I now read I probably shouldn't do anymore, just 7-10lbs) - the reseat pressure was at 16lbs. So i tried firing up, and it started, held high idle and then wouldn't idle. Tried a few more times messing with carb (low side) with same result - can keep it running feathering throttle for a bit. Then it flooded. Dried the plug, let it sit for a bit, and now it won't start at all.

I looked at the vent line.. its dry. Should fuel be in there?

It ran fine yesterday for a while... it idled fine. Today no idling.. it would run feathering the throttle... then no start at all and flooding. At this point I think I've got gremlins....

So i'm thinking that vent is screwed up (which would sort of explain yesterday's symptoms) or maybe a bad coil?
The orange umbrella looks like it belongs in there since the hole is perfect for it. That duckbill thing looks like it would require a slot or something other than a tiny hole in the tank...
I think if I understood better the function of the vent, maybe I could rebuild one to original specs?


Good news is I'm learning! Just took one of my dead echo 590s totally apart and discovered a broken piston ring, so I'm waiting for my case splitter tool and will attempt to rebuild that for practice before pulling apart one of my treasured old stihls

Thanks again!

UPDATE: I pulled the carb off, looked in the metering side and it was full of fuel. The needle seems to be operating properly (and it held pressure) so I put it back together and into the saw. Didn't touch the vent. Started it, and it fired up, high idled but sounded funny and still won't idle. Now the tank vent tube is full of fuel and actually leaking past the the little screw in there... So i get a pants leg full of fuel trying to start it.

UPDATE 2, started it again this morning, it starts, high idles, then slowly dies down. I pulled the plug, and its wet. This time I ran it with the vent tube off (altho kept the orange thing in), not much change with that. I'm going down to get some non-ethanol gas and will change that out. Going to change the carb out next. I'm not necessarily the most logical person around so I think I'm bouncing around here, but one way or another the damn thing is going to be fixed... .