Stihl screw style tank vent?

[Pioneer]

If you have a Stihl saw with the older style tank vent that has screws in a tube, you may want to consider continuing to use it after a rebuild instead of going to the newer style duck bill vent. The new style will not release pressure from the fuel tank, and it may build up enough pressure to overcome the popoff setting on the carb and flood the saw. This is what happened to me on an 025, flooded the saw badly when it went from cold to warm conditions. Put the old vent tube back in, no more problems. This may be carb dependent, it is happening on a Walbro, whereas the ms250 I have that uses a Zama does not have any issues with the new style vent.
This could be solved by going to a stiffer needle valve spring on the Walbro, but then it may adversely affect carb tuning, so the simple solution is probably the best.

 

[SteveSr]

If you have a Stihl saw with the older style tank vent that has screws in a tube, you may want to consider continuing to use it after a rebuild instead of going to the newer style duck bill vent. The new style will not release pressure from the fuel tank, and it may build up enough pressure to overcome the popoff setting on the carb and flood the saw.

This is unlikely unless the carb is defective. Get out your MityVac and try to get one to pop off under 15psi.

This is what happened to me on an 025, flooded the saw badly when it went from cold to warm conditions. Put the old vent tube back in, no more problems. This may be carb dependent, it is happening on a Walbro, whereas the ms250 I have that uses a Zama does not have any issues with the new style vent.
This could be solved by going to a stiffer needle valve spring on the Walbro, but then it may adversely affect carb tuning, so the simple solution is probably the best.

Did you actually measure the pop-off pressure on the Walbro? It is much more likely that you have a needle and seat leak which caused your flooding. These older carbs used welch plug sealant that was not impervious to ETH fuels and would chip off and get stuck in various places, including the needle.

The RVP (Reid Vapor Pressure) of gasoline is only in the 7.8 - 9.0 psi.
https://www.epa.gov/gasoline-standards/gasoline-reid-vapor-pressureSo the carb should hold 10psi indefinitely.

BTW, I have retrofitted at least one 025 with a Walbro Wt-215 with an echo duckbill without having any kind of flooding issue.

 

[Pioneer]

Quite possible there is a tiny flaw in the seat, close inspection under magnification shows nothing however. There is a new needle in place, so no problem there. I noticed that the spring is very light in pressure, I'm using the old one so age may have taken its toll.
The saw holds fuel in the carb overnight, starts easy and runs perfect with the old vent in place, so in this case I choose not to mess with it.

 

[stihltech]

So if you think the new style vent may cause problems, why use it. Clean the two screw inserts, replace the vent hose. PUSH the inserts in the hose, do not screw them in. Worked for 30 years. Still does.

 

[RedneckChainsawRepair]

I've done old 025 and others with them and never a issue. How I started replacing the grub style here.

Both work. I even make my own grub. Push in.

Sounds like you have seat issues to me.

 

[Okie]

.as stihltech says:
PUSH the inserts in the hose, do not screw them in.

I've tested with a vac/pressure mity/vac screwng the grub screw into place in the vent tube vs pushing them in.
If if you screw one into tygon it will not vent and may stop venting anyway after awhile due to the tygon being soft.
I use grub screws for the vents but I use a harder type vent hose.

 

[SteveSr]

.as stihltech says:
PUSH the inserts in the hose, do not screw them in.

I've tested weith a vac/pressure mity/vac screwng the grub screw into place in the vet vs pushing them
If if you screw one into tygon it will not vent and may stop venting anyway after awhile due to the tygon being soft.
I use grub screws for the vents but I use a harder type vent hose.

This is another good reason to use the Echo duck bill... Unlikely to clog up and lead to fuel starvation.