Light Gray Powder Residue On Carb Screen?

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SteveSr

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Hello,

Before you hurt yourself jumping to conclusions:crazy2:... Here is the full story. Saw was completely rebuilt. Carb is a Walbro Wt-22C and was run through the ultrasonic before being completely rebuilt. The fuel hose is brand new OEM (Stihl). The fuel pickup, also Stihl, looked good so I decided to reuse it.

Saw ran good through 1 tank of gas. After I refilled it I had a hard time getting it started and after I did it acted significantly fuel starved. At WOT it would burble for a couple of seconds before the RPMs started to climb. In retrospect this was the metering chamber emptying faster than the pump could refill it due to the sludge that I later found in the carb screen.

When I got home I pulled the carb out and found some gray sludge in the carb screen. I cleaned the screen over an empty tuna can. When I looked at the can today I found a light gray powder.

So considering that everything was cleaned pretty well I am obviously trying to figure out what this powdery residue is and where it came from. The new fuel line had this white powder on the outside of it. I didn't look at the inside of the line. Since the carb was US cleaned I don't think it came from there. This leaves either something in the tank or something in the reused fuel filter.

Any thoughts?

Thanks,
Steve
 
Is the powedered substance metallic? Could it be material from within the cylinder from the piston rings/cylinder wall wearing in since you said it was a fresh complete rebuild? Just tossing an idea out.
 
Drain the fuel and let the tank air dry then see if there's any residue in there.
 
Is the powedered substance metallic? Could it be material from within the cylinder from the piston rings/cylinder wall wearing in since you said it was a fresh complete rebuild? Just tossing an idea out.
Inside the carburetor? Can't tell if it is metallic or not. Once dried it held together pretty good by itself. Had to smear it between my fingers to get it to break up.
 
Drain the fuel and let the tank air dry then see if there's any residue in there.
It is currently drying as I have a delay getting a new filter and will check before installing it. The original Stihl filter appears to be sintered plastic. I am wondering if this could be breakdown components from either the tank plastic or the filter plastic. I know that I at least flushed the tank with pre-mix. I might have also done a quick rinse with carb cleaner.

The Stihl filter has that very fine screen on the outside so if the crud came through there it would have to very small particles. Yet the screen in the carb seems to have stopped it and it is a much coarser mesh. It is almost like something in the gas caused whatever to coagulate and not pass through the carb screen.
 
Carb cleaner destroys plastic and rubber so that`s a no no.
Well, the Berryman B-12 that I use says noting about harming rubber or plastics in stark contrast to the chlorinated brake cleaner I DON'T use for this. To mitigate any effects I usually only slosh around a little cleaner for less than 30 seconds. Based on what comes out of the tank it appears to be good at removing any varnish deposits left from old fuel. Normally when I do this I leave the old fuel hose in place to plug the hole. The new hose never sees the cleaner.
 
What kind of line is going to the carburetor? Nitrile rubber, black pvc fuel line, tygon, or the oem replacement? I've seen this with coated line before.
 
What kind of line is going to the carburetor? Nitrile rubber, black pvc fuel line, tygon, or the oem replacement? I've seen this with coated line before.
This was an OEM Stihl replacement fuel line. I am assuming that it is some sort of nitrile. Didn't feel slippery (or stiff) like Viton. What do you mean by "coated line"?
 
The black pvc line has a clear coating/covering on it that makes it stronger but it can break down and leaves a white powder.
 
It may be caused by corrosion from the fuel, an additive to it, or a breakdown of the plastic tank, or container.
 
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