Got a question about a tank setup.

[Paul Taylor]

In the picture below I have a yellow circle around the fill tube. It shows a yellow cap, that I remove when I fill the tank. I leave this cap off so it will get air pressure on the tank.
The red circle is on the overflow vent and I normally take this cap off for flight.
When I fill the tank sometime fuel will run out of the over flow so I leave the cap on until I am ready to fly.
Well yesterday as I got ready to launch, I checked the RPM and they were still set. As I got ready to stand up, the engine RPM change a few hundred. I tach’ed it again and opened the needle a click to get it back down.
I had a great run and nice flight. As I was looking at my computer screen today I have a picture of my Twister as my desk top, I noticed the filler caps. And I just remembered that I forgot to take the cap off the over flow vent.
Did I just get lucky on my engine run?

[Charlie Pate]

I,ll take a stab at it!
 If its a uniflo tank, the overflow tube (bottom ) must be plugged after filling.
 If its a regular tank,the bottom ,overflow, does not have to be plugged for flying.
However, I reccommend it.
If its a uniflow and you do not plug the overflow it becomes a regular tank.
That ought to do for now.
Oh ! try it both ways and see ! I,ll bet you will see a difference and will fly with it plugged from now on (provided your fill vent is hooked(facing the wind).

[Wynn Robins]

that is pretty much it.....you should always cap your overflow vent on uniflow tanks....

You should consider changing the vent caps you have there too.....they leak air and do not seal particularly well....a piece of fuel tubing with a plug of some description is a better option