550 fuel venting?

[celeriac]

While I'm wrestling with my winch problem it occurred to ask about another brain teaser. How is a 550 fuel tank supposed to vent? I've had a rash of problems getting the machine to start after it sits overnight or longer. There would be air in the fuel system, usually the filter. Round about we discovered that the fuel tank seems to be under vacuum after the machine runs a bit, or after the appropriate temperature changes. If I leave the cap unscrewed a bit when parking the machine it starts right off. I cannot see any way for the system to vent, what am I missing??

[KenP]

deleted

[srs_mn]

I cannot see any way for the system to vent, what am I missing??

Look under the fill cap in the tank right up at the top... there should be a tube running all the way through the tank and coming out the bottom of the tank... it may be hiding under the plastic filler screen flange (if it's still there)... sometimes mud wasps build a nest in the tube and plug them up...
That's the way my 350C's and 450C's were vented - I'm pretty sure a 550 is the same.
srs/MN

[celeriac]

Thanks! I see the tube and where it should come out at the bottom of the tank. I tried to run a wire through and it's blocked at both top and bottom. At the top there's something about 5" down and the underside is blocked right at the bottom with something tougher than mud. Is there some sort of packing or steel wool in there?

[mini kahuna]

sounds like a mud dauber got you,those mud wasps love vent tubes on jd crawlers!!!!