Husqvarna 335xpt Fueling Issue

[Snap]

My 335xpt runs fine until it gets to about half a tank of fuel then it peters out, acting fuel starved. If I remove the fuel tank cap briefly and let it sit a few minutes it fires up and runs again. Sometimes it quits twice per tankful. The filter ( fairly new) appears to be down in the bottom of the tank. The spark plug shown no signs of problems; good color, not wet nor sooted. Carb is fairly new and has been adjusted. I wondered perhaps if the gas fill cap or tank might need a vent of some sort. Any ideas?

 

[SEAM]

There is a vent (sintered metal strainer and spacer, P/N 503 60 04-01 and 501 62 98-01 on page 4 in the IPL) behind the bar attachment side plate, which most probably is blocked by soil... To access the vent for replacement quite a few parts need to be removed, if I remember correctly (sold both my 335XPTs a while ago).

IPL: https://www.google.co.jp/search?q=335+XPT+ipl&ie=&oe=

A vented cap might be an alternative solution...

 

[old guy]

I drilled a hole in the cap for a rubber duckbill, problem solved.

 

[Snap]

I drilled a hole in the cap for a rubber duckbill, problem solved.

What does a rubber duckbill look like?

 

[Snap]

There is a vent (sintered metal strainer and spacer, P/N 503 60 04-01 and 501 62 98-01 on page 4 in the IPL) behind the bar attachment side plate, which most probably is blocked by soil... To access the vent for replacement quite a few parts need to be removed, if I remember correctly (sold both my 335XPTs a while ago).

IPL: https://www.google.co.jp/search?q=335+XPT+ipl&ie=&oe=

A vented cap might be an alternative solution...

Would it get soiled from inside or outside the tank? If outside, where is it seen?

 

[SEAM]

The vent may get clogged by drying 2-stroke oil when the saw is in storage (fuel vaporizes with the oil remaining), or the clogging could be caused by dust in the air vented into the tank.
I once resolved clogging by spraying excessive amounts of oil (Jap. version of WD 40) in the vicinity of the vent from inside the empty tank and outside in between the bar mount and the case on one of my 335XPTs... may have been purely coincidental, but the problem never recurred.

Another possible cause might be a clogged strainer in the carb (loose particles)...

 

[Snap]

The vent may get clogged by drying 2-stroke oil when the saw is in storage (fuel vaporizes with the oil remaining), or the clogging could be caused by dust in the air vented into the tank.
I once resolved clogging by spraying excessive amounts of oil (Jap. version of WD 40) in the vicinity of the vent from inside the empty tank and outside in between the bar mount and the case on one of my 335XPTs... may have been purely coincidental, but the problem never recurred.

Another possible cause might be a clogged strainer in the carb (loose particles)...

New strainer on the fuel line and the tank looks clean.
Will try spraying the vent filter but lan on adding a vent in the filler cap. Seems to be the easiest thing to access.