038 carb perpetually blocking up?

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Ibeatgodzilla

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Hi all,

I've had an 038 AVS Farm Boss with the Bing 48 carb for 5-6 years now, only had occasional use under my ownership as a secondary saw and spent the latter half of that time feeling a bit redundant at the back of the barn after I bought an 066.
I recently decided to dust it off and give it a well-needed rebuild with new barrel and piston - now going very strong - to keep in reserve as a backup saw for bigger jobs should anything go wrong with the 066.
Thing is, it's always had this issue where the in-carb filter keeps blocking up during use; obviously causing the machine to play up, stall and not want to start again until you've dismantled the carb, cleaned it out, and reassembled it. I've done that countless times. But it's a bit of an inconvenience - especially when it can happen multiple times in a day - and doesn't make you look "wasting time tinkering with an unreliable machine" during paid jobs.
The carburetter gasket/membrane set was changed during the saw rebuild; the problem persists nonetheless.

I've never had this issue with any other chainsaw or garden machine, and I run quite a lot of them. First thing I tried was swapping out the fuel filter in the tank, with the theory that perhaps it was letting through some tiny particles that in turn got stuck in the in-carb filter; unfortunately that didn't fix it. I use the same fuel mix from the same gallon can as I do in my other machines, which don't block up, and having already tried two in-tank filters kind of eliminates dirt in the tank from being the source of the blocking particles. The tank itself was thoroughly cleaned out when I rebuilt the saw. More recently upon further inspection I came to the conclusion that dust particles must be coming through the little hole at the top of the carb (pictured) as the chamber underneath is always full of dirt and somehow passing from there to the little filter (not sure how they would get past the gasket), and blocking it.

Surely if this was the case it would be a known issue with this model, however I find no other threads mentioning it. Has anybody else experienced this? Any other ideas as to what the cause and solution may be? Seems a shame to change the carb when it's the original, and working very well when it isn't getting blocked.
 

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thats the diaphragm breather hole, highly doubt the fibers are entering into the fuel stream at that point. do not block that hole. you have fines in the fuel tank passing by or through the fuel filter or entering in through the fuel tank breather.
 
I would change the fuel hoses. They could be coming apart from the inside.
This^^^^^ and at times I have found that a thin layer of varnish like coating had previously formed inside the fuel line and then flakes off filling/ blocking the carb screen. Change out the fuel line.
 
Thanks for the thoughts guys.
I did indeed presume that Bing put that hole there for a reason so didn't intend on blocking it.
Theoretically, it could be fuel lines... But they were replaced during the rebuild.

Sounds like I just need to repeat what I've already done then - clean out the tank, try another fuel line+filter...


Unrelated but possibly a lethal coincidence - saw an MS461 at a second hand shop for €400 today. That's a good price here in Europe. I have the 038 and the 066, and no need for the 461... But there again it is a fair price and somewhere between a dozen and a couple dozen of my machines fall under the 'I don't really need them' category anyway...

Out of curiosity, does anybody know how the MS461 would compare to the 038 (magnum spec with its new 72cc barrel) and 066? Not just numbers but use, 'behaviour' ?
 
Next time you have fuel starvation symptoms, try loosening the fuel cap (orient the saw so the fuel doesn't all pour out) to check for defective fuel tank vent. Maybe there is some air leakage between the carb fuel inlet and the fuel line. I put some of this on the metal tube on the carb, put the fuel line on, let it dry for 24 hours. This is supposed to remain gooey for a while so I might have been able to still remove the fuel line today if it hadn't worked. Let us know if your figure it out, even if it is something stupid, especially if it is something stupid, to save us from the same stupid thing. DSCN5222.JPG
 
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