Comment

Comment by Peter Bennett on May 23, 2011 at 11:39am

I've ordered new fuel caps from Zenith for a starter. They should arrive any day.  So far I have a few thoughts on possibilities: (1) a partial vacume is created around the fuel caps that effects equal fuel flow from the tanks when in flight, (2) lots of folks are experiencing this issue to some extent, (3) the problem might result in engine failure, and (4) it therefore may be a Zenith safety engineering issue. Remember, I was on an extended cross-country flight and experienced engine failure with plenty of fuel in the right tank, so at least in my case Jimmy's suggestion didn't work out.

 

By the way, I really appreciate all the feedback concerning this issue.  Thanks to everyone for sharing your experiences and ideas.

 

 

Comment by Jim Derickson on May 23, 2011 at 8:57am

Perer, I have the o-200 also. I increased the vent hole in the caps to 1/8 th inch, still had uneven fuel flow. I also notice after a flight you still have unequal pressure in the tanks when you remove the caps. ( they equalize ) I went to the cessna style caps from aircraft spruce, they also don't allow the air in the tanks to equalize. I also changed my fuel lines so they are the same length to the fuel selector valve. I still don't have equal flow from the tanks and don't think I ever will. That said , I have run the tanks down to none measurable in the left and 6 in the right and still running, ( Jimmy stated his thoughts on this )  I just came back from a long cross country and had to extend farther than I had planned for fuel, I had 2 gal in left and 3 gal in right, so when you get down to it I guess I had a some what even fuel flow. I think that Clemens has the solution with the ram air vents, I don't like the looks of them, but I like the engine to get all the fuel it needs!

Comment by Peter Bennett on May 19, 2011 at 3:11pm

It is interesting how common this issue seems, to a greater or lesser extent. The gas caps seem to be the culprit.  I am getting two new caps from Zeniyh, but I now suspect that Clemens's solution will be the ultimate solution. Clemens, specifically, what did you order . . . and, how much?

Comment by Clemens Kramer on May 19, 2011 at 11:53am

I noticed in draining my tanks through the gasloator that the volume of gas drained faster than the same volume of air could enter the tanks to equalize them, an therefore created a slight vaccum an slowed(did not stop) the flow of gas. Take the caps off and there was a release of pressure( my guess is the vent holes are not big enough for 3/8" fuel lines). My cure was to buy from Wag Aero the old style caps with the copper tubes protuding from the top and pointed forward, creating positive pressure on the gas in the tanks. My left tank always has more gas than the right, about 2 gals, don't know why

Comment by Jimmy Young on May 19, 2011 at 4:55am

Let's assume one tank runs dry, the other has 6 gal. left. Wouldn't the fuel simply continue to flow from the tank with fuel, and the dry tank is just another vent line in the system at that point? If so, as long as the lines tee together per plan and you have no selector valves, it seems to me there would be no problem.

By the way Peter, I'm just up the road in Houston, building a 750. We should get together & meet, as close as we are.

Comment by Harmen van der Velden on May 18, 2011 at 6:29pm

my 701 always uses more fuel from the left , than from the right, perhaps i am not flying straight (wings not really level???) may be but another variable in my set up is that the gascolater is on the left, and that makes the right fuel line longer, and therefore more resistant to flow. I have a valve in each line and have considered flying the first half hour on the right tank only and then switching the way we do it in a piper without a "both" setting. Never have run into a dangerously low tank yet , but I happened to have a built in safety feature (aka a 2 hour bladder!)

Comment by Peter Bennett on May 18, 2011 at 4:50pm

Thomas,

 

Interesting comments that suggest I'm not the "only one."  I am ordering two new fuel caps from Zenith for starts.  Then I'll have a couple to experiment with. The Cessna idea also holds possibilities.  Thanks!

Comment by Thomas Richardson on May 18, 2011 at 4:43pm

I am curious about your statement that as soon as you land they even out yet you measured 6.5 in one and 9.5. in the other. My 701 has a tendency to drain the right tank first until it gets to about a half a tank and then the left starts to drain. Might sound silly but I think it is due to a tendency for pilots to make more left hand turns than right and in my case , the airport has a left hand pattern. It seems in my case to be a simple gravity issue. My plans called for a 1/16 hole to be drilled in the top of the caps to help flow. As soon as I did this, the flow issues lessened. Some guys have moved on and bought the cessna caps.

Comment by Peter Bennett on May 18, 2011 at 4:32pm

1. Continental O-200 2. Have to measure  3. Don't know  4.  One, common to both tanks after the feed meets

 

5.  No selector; each tank comes together in a "T" junction.

 

The tanks soon equal out after landing.

Comment by Jonathan Porter on May 18, 2011 at 2:35pm

1. What engine.

2. Fuel hose diameter.

3. gascolator position, type

4. Fuel filter(s)

5. Fuel selector tap type

perhaps info on that will help direct comments...

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