So, I am thinking about replacing the carb on my PP5020AV, and when I look at ebay and elsewhere, all of the "compatible" carbs have a single throat. When I pull the air filter off the saw, I see two throats. Does anyone know what the story is? Has the carb style changed over time? Do others with the same saw have the 2 throat carb or a 1 throat carb?
If it's like a lot of other Husqvarna hardware, the strato butterfly (that 2nd throat you see) detatches from the actual carburetor.
Yep, it seems that it is called an air valve, and not part of the carb. Interesting, how does it work differently than a stand-alone carb?
Basically a Strato-charged engine will fill the crankcase from both the intake ports and the transfer ports. The intake port carries a rich fuel/air mixture and clean, fresh air flows in from the top of the transfer ports via some wild looking passages on the piston. The idea is that any scavenging losses, which are inherent to a 2 stroke design, will be only clean air and no raw fuel is expelled from the exhaust.
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I've heard others, some self-designated experts on stratos, claim that strato induction systems send extra-rich mixtures to the crankcase. Whereas what goes that way is just suitable mixture for eventual combustion via the transfers, with the transfers getting a shot of air-only, at their discharge end, to be dumped out the exhaust port during short-circuiting. Not gonna name names. May be semantics, but it seems to confuse some, so it's not a nit-picky thing.
Thanks for the help with understanding the strato. I found 2 things that were making the saw act a little wonky. First, the choke was not opening properly, it would go "over-center" past the little stop tab in the throat of the carburetor, so it was about 1/3 closed the other way. I fixed that by fabricating an external stop on the linkage so the choke plate is aligned with the airflow when open. Second, the strato air valve wasn't opening reliably because of a linkage problem, one that I caused. So fixed that. I put a new air filter on, removed the screen from the muffler, and elongated the holes on the ignition coil to shift it a little advanced from factory (about 1/16"), no idea how many degrees, but not much. I set the carb and it runs better than it has in a few months. It is hard to hear the 4-stroking on that saw, compared the Husky 141, but it seems to be happy about 1/2 turn rich of max RPM. Greg
Glad to hear you got her running good. Funny you say it's hard hear the 4 stroke, I can hear it pretty distinctly on that saw, my 55 not so much
Maybe I should try just a little richer. I'll see how it sounds when I have the chance to run it more.
I had to tune mine as soon as I started it the first time, if it's barking out of the wood and cleans up when you get it in the wood it should be pretty good
HDRock I see you run a 16" bar on yours. I am still running the 20" with lpx chain. How much difference does the 16" make?
The bigger the wood the bigger the difference, cutting a 6-8" Log, not much difference at all, you get up to about 12" makes quite a bit of difference, and if you bury the bar nose, even a bigger difference. I put a woodland Pro, bar and chain combo I bought on it $40, better balance to it I think. I cut up a bunch of oak with the stock bar before I got the other one I wanted to do a one after the other test with both bars and sharp chains, haven't done it yet though. I have an Oregon lgx on it right now, the Woodland chain is basically the same thing
