Underpressure in gas tank?

[t_andersen]

Hi Guys,

I use a Stihl 064 for chain saw milling. It has been somewhat hard to start so I have bought a new carb that I will mount on the saw when I get the time. I was running the chain saw the whole weekend and towards the end it stopped quite suddenly on a couple of occasions but I could get it back running after waiting for a few minutes. I also noted that there was a slight underpressure in the gas tank when I opened the lid to refuel.

My question is: Do you think that the underpressure could lead to a sudden stop? Is there a ventilation hole in the lid for the gas tank and how do I clean it?

At first, I suspected dirt in the carb but if that were the case I guess it wouldn't get back running after a few minutes?

I have measured the compression some months ago to 125 psi.

Thanks for any advice.

Regards
Tom

 

[Lakeside53]

No "underpressure" in the tank... the tank needs to be at atmospheric pressure. Sounds to me like the tank vent is not working... It is supposed to allow air to enter the tank as your gas is consumed. You pump cannot work against the negative tank pressure so it quits feeding gas.

The tank vent is not though the cap - it is the tube on the left side of the tank that curves out to the front. In the end is a grub screw. Remove the screw and clean it. Best solution is to replace the tube with a new piece as the plastic swells around the screw and stops air leaking passed it.