If anybody could help I would appreciate it.

My 750 is nearly complete at as a kit.  When I built the wings I ran the supply fuel lines at the lower fitting and the vent line to the fuel tank on the opposite side on top of the tank. At the time I didn’t consider what type of engine I was going to install. Now that I have decided to install a fuel injected engine, I realize that I need use the vent lines I ran  for the return of the fuel to the tanks. But because there are only two fittings in each of the fuel tanks I don’t know how I am going to be able to vent the tanks at this point. I’m going to be using an “Andair” duplex fuel selector valve to return the fuel from the same tank that it was taken from. What I would like to know is there any way at this point to vent the tanks without disassembling the wings and if not, where do I install the vent lines?

I’m sure by now you realized this is my first build.  I would greatly appreciate any suggestions.  Thanks in advance,      Bob

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Comment by Geoff Klestadt on February 9, 2014 at 12:09am
From my diesel experience DO NOT tee the fuel return line into the inlet line or the top of the gas collated because if you do that, any bubbles introduced into the system cannot clear and the engine will stop.

You need to get that return line back to a header tank or main tank so the bubbles can separate out. The three videos on the rotax owners builders video website explain the problem and their solution in detail.
Comment by Lawrence Van Egmond on January 31, 2014 at 7:13pm

I have the Zenith vented caps and mine don't vent. Check them carefully because some of the caps were pressed to tight and don't vent.

Comment by Marvin W Miller on January 29, 2014 at 8:55pm
You didn't say which fuel-injected engine. If its a Viking looping the return back to the gasolator won't work. I tried it. To many bubbles. A vented fuel cap might just be your best bet.
Comment by Kimbull McAndrew on January 26, 2014 at 10:56am
PS If you belong to Rotax Owners you can view a series of videos on the Sky Tek design for the installation of a 912is in a 750. There are a lot of details on fuel system design there.
Comment by Kimbull McAndrew on January 26, 2014 at 12:46am

I agree with Andrzej that a header tank or venting to the main tanks is required. If you check the Sky Tek Canada design for the 912is they put a lot of effort into venting, using 1/2 inch lines between the header tank and the wing tanks nand venting the vapour return line into the header tank. I have to disagree with Doug's suggestion of venting to the gascolator because if you vent there there is no place for the vapour to escape and it will remain in the line feeding the engine causing fuel starvation due to vapour lock.

Comment by Andrzej Kostkiewicz on January 25, 2014 at 5:27pm
If You decidet to install injected engine You have to instal heder tank for coolng fuel behind sits .. i am flying on 701 with BMW inected engine and this setup works well .
Comment by Doug MacDonald on January 25, 2014 at 1:02pm

Bob, standard Zenith fuel caps are vented.  The additional fuel fittings at the outboard top of the fuel tanks are optional vent/return ports.  On the 750 I built we didn't even use the extra port and filled it with an aluminum pipe plug.  In fact, the additional port was only on the left side tank as the tanks we used were some of the first to come with the new fittings.

One other place you might consider returning your excess fuel too is the top of the gascolator.  I'm not sure if the  Zenith gascolator has the extra port on top but the basic homebuilder's gascolator from Aircraft Spruce does.  With the gascolator ideally being upstream of your fuel pumps, it will back feed to the tanks without having to run a complete set of return lines to the tanks.

Another thing to consider when running fuel lines is the material the lines are made of.  I personally will not use the black rubber automotive grade fuel line Zenith sells for their kits.  You are building an airplane, use aircraft grade fuel lines and fittings (ie: 3/8" aluminum line and AN fittings).  The  additional costs involved in installing a proper aircraft grade fuel system are well worth the piece of mind.  I have experienced the black rubber fuel hose swelling internally and cutting off fuel flow on a classic car I have so figure it is an accident waiting to happen if rubber fuel lines are used on an aircraft.  Maybe I'm just picky but the electrical and fuel systems on both of the planes I have built have adhered as close as possible to standard aircraft methodology.  These standard systems have been developed as the result of accidents caused by systems that did not work as intended.  Yes, genuine aircraft components are more expensive but you know they will work as intended.

Hope this info is of some help.  Best of luck with your build.

Doug M

NW Ontario, Canada

Comment by Bob Fairbanks on January 24, 2014 at 10:21pm
Thanks Kimbull, I never realized that the fuel caps could possibly be vented. I'll check them out tomorrow. I hope your right. Thanks a lot for the feedback so quickly.
Comment by Kimbull McAndrew on January 24, 2014 at 9:18pm
The fuel caps I received from Zenith are vented so you might not need a separate vent line from the tank if you received the same fuel caps. If you check your caps you will find 2 or 3 small vent holes on the fuel side of the rubber seal and 4 small vent holes just inside the outer edges of the underside of the fuel cap if you did receive vented caps.

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