Tank Vents

[RES]

I have several Stihl 020av's some fairly new, some old. From my observations they all vent through the fill cap. One of the caps has a screw that threads into a soft plastic insert in the cap. The others seem to have a hole in the cap with some internal workings that prevent the gas from leaking out. My 038 has a plastic tube with a screw in it. I am curious how the screw vent works. Does the air work its way around the threads to vent. How do you know if it is venting properly? Should this screw be bottomed out?

 

[Lakeside53]

I have several Stihl 020av's some fairly new, some old. From my observations they all vent through the fill cap. One of the caps has a screw that threads into a soft plastic insert in the cap. The others seem to have a hole in the cap with some internal workings that prevent the gas from leaking out. My 038 has a plastic tube with a screw in it. I am curious how the screw vent works. Does the air work its way around the threads to vent. How do you know if it is venting properly? Should this screw be bottomed out?

It works, kind of, because their is a tiny gap between the threads and the plastic. Air can get though the gap, but liquids get hung up... Not the best design and no longer used (EPA). The plastic tends to swell over time and block the thread gaps. best was to make sure it vent properly is put a vacuum pump on the gas line and make sure it lets air into the tank slowly.. Symptoms of a vent not working are varied, but reluctance to start, running lean after a few minutes, or won't hot start, are common.

 

[RES]

Thanks Andy
I think I will run a tap thru the thread and clean it out a little.

 

[Lakeside53]

Thanks Andy
I think I will run a tap thru the thread and clean it out a little.

I think it's a "Special Thread"... if you get the wrong thread you may end up with a leak (more then normal!). Check it with pressure or vac...

 

[RES]

Believe or not it was a 6-32. I tried the set screw on a 6-32 nut and it fit perfectly. I was surprised that it wasn't metric. The tap didn't make much differance. It does let some air thru but not quite as much as the older style cap.