Fuel Venting from Vent tube

[DesertFox4]

Sorry but I don't understand the reason of DesertFox closing the holes that are outside of the cap's gasket. It seems pointless.

This has solved fuel overboarding for a couple Kitfoxs and also as Lowell stated if the cap integrity is compromised you lose some ram pressure from the fuel cap which may be causing some to experience unequal fuel drain from their fuel tanks. Might seem pointless to some but has helped in some instances. Sure helped my model 3 years ago. Hurts nothing to try even if it has zero effect.
My new caps will get this treatment before first flight. That and the blue Mercedes cap gaskets.

[jiott]

I really appreciate all the good replies and will try to answer the questions asked:

John Evans-Yes I have the fuel return line, the optional kit from Kitfox installed exactly as they say. It does tee off from between the fuel pump and the carbs thru an orificed (factory supplied) fitting. It goes directly to the side of the header tank thru a check valve. It should have nothing to do with the vent line from the header tank to the right wing tank.

Papua Pilot & others-Yes I will admit I quite often fly with 1/2 ball to the right because I need to add a little more right rudder trim tab. If I don't keep a slight right rudder pedal pressure it flies 1/2 ball to the right. Maybe you guys are on to something here!

DessertFox4-Yes I have used Hysol to close those 4 little holes in each cap based on your previous post. However I do agree that it probably is unnecessary.

JPitkin-It is possible I may be flying with the right wing low at times due to the unbalance when the right wing has more fuel in it than the left, which is quite a bit of the time. I will consciously try to avoid this and see if it helps.
I also noticed that my fuel cap vent tubes are close but not perfectly aligned with each other; will fix that.

I will report back after acting on these suggestions. Meanwhile any other advice or comments are welcome.

[PapuaPilot]

I bet if you line up your vent tubes and get your plane trimmed so the ball is centered in cruise the problem will disappear.

[jrevens]

When I leak checked my tanks, I introduced a small amount of refrigerant into the tanks, and pumped them up to 1/2 psi, then used an electronic leak detector to check them (I was in the refrigeration business for years). I have the blue Mercedes gaskets. I never could get a perfect leak-free seal at the caps. That being said, and in taking another look at the caps, there is another possible path to the 4 vent holes that DesertFox4 pointed out. That is from the 2 rivets holding on the latching piece. There is probably leakage around those rivets, maybe more with some than others. I'm going to seal those holes also... thanks Steve!

[DesertFox4]

John- The rivets can bypass also. I appreciate your in depth testing of your caps. Most don't have the means to thoroughly test as you did.
I believe also the original fuel caps two pieces, before the ram pressure tubes are added, are not welded but crimped together. That is why I also sealed the entire way around the caps crimped joint with J.B. Weld. It doesn't show well in the link to the photo in my previous post but it is there. I forgot to mention that little point. Sorry. You could get a leak on the crimped seam anywhere around that edge.
If I recall, these caps were made for tractors and converted for our use. They likely were never meant to be pressurized in their original configuration.

[jiott]

Have double checked the alignment of my fuel cap vent tubes and tweaked them a little; actually they were very close to being OK. Am now working on a better rudder trim tab to eliminate the yaw tendency to fly 1/2 ball to the right. Will let you know how this turns out.

[jiott]

Just installed my new rudder trim tab and also thoroughly checked my fuel cap gaskets and sealing to make sure there are no leaks to bleed off pitot vent pressure in either tank. Everything checked out good. Then went for a test flight with the new rudder tab. After tweaking the tab bend angle slightly it now flies with the ball centered as perfect as I can get it. It made an immediate improvement in evening out the fuel drawdown rate from each tank. The right tank now does not tend to stay full but comes down with the left, not perfectly even, but probably as even as possible. I will have to say I was surprised that 1/2 ball of uncoordinated flight could make that much difference in fuel flow out of two tanks tied together thru a header tank. I need to go out now with a friend who will follow me and see if my intermittent fuel vent vapor trail has stopped.

[jiott]

My fuel vapor trail has stopped. Now only vents fuel if I do a somewhat aggressive slip with nearly full tanks.