Fuel line size for Lycoming installation

[redbowen]

For those that have installed a lycoming in their Kitfox can you tell me what size fuel line you used from the header tank forward and where, if any, reductions you made?

I'm installing a fuel flow computer and have found some things in the fuel system that don't seem ideal. For example the header tank fuel out line is 1/4 to a shut off valve that is reduced to 1/8 then back up to 1/4 to the gascolator, then reduced back to 1/8 to the carburetor. I would think the middle reduction is not a good idea, can anyone give there input on this?

The current system passed the flow test requiring about 15 gph from gravity, but I would like to have a constant size until the final reduction into the MA-3SPA carburetor.

Thanks for the input

[rainbird]

I'm also faced with the same problem, the restriction in the fuel line at the shutoff valve. I will be using a 2276cc VW engine that requires a 1/4" fuel feed line. My shutoff valve ID measures 3/16"..I talked to a fluid engineer about this and he felt the1/16" restriction would cause turbulent flow and restriction. So I'm trying toget up enough nerve to run a1/4" drill or ream through that $75.00 valve. Both the ball valve and the body are brass and only the ball itself is undersized. Any thoughts or suggestions?

[Av8r3400]

I would suspect the ball in the valve is hardened and may not take well to being reamed. If it hasn't been used, maybe it can be returned or exchanged for the larger size?

[N981MS]

IO240 Continental with stock fuel valve. I do not remember the orifice on the valve. I also early on had the facet pump which I think has a small orifice. It was an all stock Kitfox setup for this engine at the time. No problems.

Got a bit worried that the facet pump would not run the engine if engine driven pump failed so I changed it to a pump that would.

YMMV but if it flows 15 gph it flows 15 gph. If you are worried about a chunk of something obstructing something at the 1/8" valve I bet it will have a slightly delayed but similar result at the 1/8" carburetor restriction. I think I would leave it alone. Use the recommended finger strainers and fuel filters of course.

Bottom line is build it the way you want and that gives you that warm fuzzy feeling.

[HighWing]

I think I am pretty much with Maxwell on this one. I checked the early Model IV firewall forward section and I suppose for the slightly higher fuel consumption of the then more popular 582 the book calls for 5/16" hose from the wing tanks to the header tank then 5/16" aluminum tubing from the header tank to the valve and the then recommended gascolator. 5/16" hose then to the fuel pump then quarter inch to the carburetors. Definitely a different system, but suspect the larger diameter lines was to compensate in part at least to the restrictions through the fittings, valves etc. I suspect if your system recommends quarter inch, the engineers that designed that recommendation understood the restrictions in the fittings etc.

[n85ae]

3/8" in mine with IO-240B, mostly aluminum, and braided at the wing
roots.

Jeff

[redbowen]

So I wanted to do an update. The fuel line from the header to the gascolator is 3/8 aluminum with AN6 fittings. The fuel valve was 1/8, AN 4 so it stepped down at the fuel valve then back up to AN 6 3/8 line. AN 6 is ID 1/4". From the gascolator to the carb I have an aux fuel pump primarily used for starting, instead of a primer system, it also comes in handy if the low fuel light comes on it allows me to pump the header nearly dry. The fuel pump has AN 4 fittings in and out of it, so its 1/8 ID. I have not found a alternative pump that would give me the proper fuel pressure maximums and have larger fittings. From the fuel pump it steps up to an AN 5 flex line to the carb.

Things I changed:
I removed the old fuel valve and put in a larger one from Kitfox. All AN 6 fittings, so its 3/8 OD in and out. I put the FT-90 fuel flow sensor between the fuel valve and the fire wall, again all AN 6 fittings.

From the Gascolator forward I left the same, but will continue to look at ways to keep a larger line all the way to the carb.

Thanks for your comments.

[jtpitkin06]

AN 6 fittings and fuel lines are a good size for most 100 to 150 hp engines. But note that some fittings are more restrictive than others.

The photo below shows two AN6 fittings. The one on top is a full flow bend with 3/8 inch ID. The fitting on the bottom has just 1/4 inch opening on one end. Also, the hard 90 degree turn on the lower fitting will restrict flow.

if your MA3-SPA has a 1/8 inlet, you can change the inlet fitting to use Up to AN6 3/8 inlet.

John