dolmar 420 pressurizing fuel tank

[holeycow]

My little Dolmar is slowly running lean in continuous running. The fuel tank is pressurized (vaccumed) over time and the saw gets really boggy.

It has built vaccum in the fuel tank since new, but lately it is becoming a problem.

My guess is tank vent?

Maybe someone could point me to likely culprits on this particular saw.

I looked under the hood. All my lines are black.

It is about a 2010 saw...

Thanks for any help

 

[blsnelling]

A faulty tank vent is the only think that can allow vacuum to build in the tank.

 

[holeycow]

Thank-you!

That is what I will persue.

 

[lenbates]

A faulty tank vent is the only think that can allow vacuum to build in the tank.

Solved the venting problem on my 7900, after replacing the vent with a new one. I was able to order Echo Part#13131406320, and just installed and tested it. Problem completely gone. Not surprising that an Echo part would do the trick; I never have such problems with my Echo gear. The design looks identical. Maybe the problem is down where the Dol/Kita nipple sits. This vent takes a 1/2" hole, cleaned up. Presses in with a smooth low profile and holds tight. I made a few cuts, idled a while... no leaning out. Wish I could find the post where it was suggested so could thank him.