Fuel line routing - question

lostpilot28 · #1 03-06-2010, 05:19 PM

I know there were some previous posts about this - I've reviewed them over and over...but I would like to get an opinion on my setup. First a little background: I've been flying my RV-7A for the past year with the fuel line from the mechanical pump to the carb running very close (too close) to the exhaust for about 5 inches or so...probably about 1 inch away. I had a 90-degree fitting off the carb and the line went aft and down about an inch to the outside of the engine mount. I had the fuel line attached to another engine mount tube as the fuel line curved up to the fuel pump. I also had 2 heat deflectors on the exhaust to prevent the fuel from getting hot - mounted about 2 inches apart (so there was a gap between them). As in the picture below, I also had adhesive-backed aluminum wrapped around the fuel line as an added measure to help keep heat off the line. No clue if that helped, but I wouldn't think it would hurt. I had 2 different instances last summer on very hot days where if the engine heat soaked for 5 minutes (to refuel, for example) that when restarting the engine it ran very bad...I'm guessing the fuel was boiling and I had get it through the carb for it to start running well.

So, that didn't sit well with me! I rerouted my fuel line today, as in the pictures below. I used the aluminum 45-degree fitting (I may buy a steel one eventually) and now I only have about 1 inch of line that's an inch away from the exhaust, and I have the heat-shield directly under it. The rest of the line moves aft and up very quickly and adds good distance between the fuel line and the exhaust.

Is this acceptable? I've been trying to figure a better way to route the line, but this is it. Unless I buy a longer fuel line and get some really sharp angled fittings I don't think I've got many alternatives. What do you all think?

http://www.flickr.com/photos/2250766...83048/sizes/o/

http://www.flickr.com/photos/2250766...n/photostream/

Bevan · #2 03-06-2010, 07:49 PM

I haven't done my engine install yet but a couple notes:

I think you will get more distance between the fuel line and exhaust by putting a 90 fitting on the carb and angle it aft and slightly up. The fuel line will then be postioned to go over the engine mount tube futher away from the exhaust.

Keep the heat shields on the exhaust. Image the exhaust as a cherry red color when flying.

Make a longer section of orange thermal tubing to include covering the fittngs and secure at both ends with stainless safety wire.

Secure the fuel line near the carb with an adel clamp to relieve vibratory stress on the alum fitting which would be better in steel.

My 2 cents.

Bevan

lostpilot28 · #3 03-07-2010, 12:17 AM

Hi Bevan,
Well, I can't put the 90-degree fitting on it and angle it up without having a banjo fitting. Both 90-degree fittings I've tried both index at the point where they point aft and down when they tighten up. Anything less tight (to point up, even a 6th of a turn) is too loose and it'll leak fuel. My only alternative in this regard would be to double up on the copper washer under the fuel screen inlet.

Without going into some major modifications with getting longer fuel lines, etc, I just want to know if others have the same fuel-line routing that I've got pictured. It seems like that's what the plans have so that's what I changed my setup to be like. Any other thoughts?

lostpilot28 · #4 03-09-2010, 07:32 PM

Bump to the top...hoping someone could tell me if my setup is unsafe or not!

As an alternative, does anyone know if doubling up on the copper washer at the carb's fuel inlet is OK to do? Any help is greatly appreciated.

apkp777 · #5 03-09-2010, 08:08 PM

Looking at the responses to your posting, I can tell no one wants to touch this one. Sorry I don't have much to offer. I have yet to install my engine.

Here's my take on your situation. Clearly you've tried to find a routing that would keep you away from the exhaust. I think your heat shields are going to be very effective. I see you have about 1 inch of separation from the exhaust. Though not ideal, I doubt that you are heating the fuel too much.

As far as adding a second copper washer (I suppose to clock the fitting differently), I don't see a problem with that. Copper is used as it is pliable and will conform to any casting abnormalities. A second washer shouldn't make a difference.

This sort of dilemma would drive me crazy, I can see you are concerned as well. Keep this post alive and someone with more experience than both of us will chime in.

lostpilot28 · #6 03-09-2010, 09:15 PM

Quote:

Originally Posted by apkp777

Looking at the responses to your posting, I can tell no one wants to touch this one. Sorry I don't have much to offer. I have yet to install my engine.

Here's my take on your situation. Clearly you've tried to find a routing that would keep you away from the exhaust. I think your heat shields are going to be very effective. I see you have about 1 inch of separation from the exhaust. Though not ideal, I doubt that you are heating the fuel too much.

As far as adding a second copper washer (I suppose to clock the fitting differently), I don't see a problem with that. Copper is used as it is pliable and will conform to any casting abnormalities. A second washer shouldn't make a difference.

This sort of dilemma would drive me crazy, I can see you are concerned as well. Keep this post alive and someone with more experience than both of us will chime in.

Thanks, Tony...I appreciate your reply. My thinking is the same as yours regarding the copper washer. Also, from what I can gather, it seems that my new fuel line routing is what Van's intended - at least that's what it seems like when I reviewed the plans and previous posts from others with the same problem. I think the single heat shield was the factory's way of overcoming the fuel-to-exhaust spacing issue.

Either way, it has to be better than my previous routing which did let the fuel boil (apparently) if the engine was heat soaked.

If anyone else has a better idea, I'd love to hear it!

Bob Axsom · #7 03-09-2010, 10:37 PM

I have the metal heat shield on the exhaust pipe where you have a couple of them. I have a fire sleeve on the fuel line. I have no problem with the fuel system at all (~600 hrs). When I start the engine after it is hot as after a hard long run and a fuel stop I do not prime the three cylinders with prime lines otherwise the procedure I follow is the same as when it is cold. I do have a LASAR ignition system so there may be some differences in the startup condition between mine and yours. I don't think your startup/running problem after a heat soak is due to the routing of your fuel line into the carburetor. The fuel that is supplied to the engine comes from the chamber in the carburetor not directly from the input fuel line. I would get rid of the aluminum foil and study the problem more. Due you have an aux. pump in your system? Do you see fuel pressure in the input to the carburetor before you "turn the key"?

Bob Axsom

Bob Axsom

mahlon_r · #8 03-10-2010, 05:03 AM

Check out AD 95-26-13. It is on oil cooler hoses and routing of them. Although not fuel lines per say, the lines are made of the same material and the FAA says maintaining a 2 inch clearance between oil cooler lines and straight exhaust pipes with no heat shield on the pipes and only fire sleeve on the hoses is acceptable. I would think the same clearance would be acceptable with any fluid carrying line and an exhaust pipe, as far as line clearance for proximity to a heat source and line deterioration from it. I think they do want you to check the line for flexibility every 100 hours at that clearance.
Just a point of reference, that might be helpful.
Good Luck,
Mahlon
?The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."

Scott Hersha · #9 03-10-2010, 06:33 AM

Sonny,
I'm not a qualified expert, so maybe someone else can tell me if I'm wrong, but in my opinion you have a couple issues that should be considered. First - the engine shakes, the engine mount doesn't. For that reason, I don't think you should be attaching the fuel line that is connected to engine on both ends to the engine mount. Maybe there's a more flexible way to make this attachment if you have to so that it doesn't hold the line rigidly and cause a stress point. Next, if there's any way you could route the line from the pump to the carb inboard of the engine mount, that would keep it clear of the exhaust and not running above the exhaust for several inches. Cowling interference may pose an issue not evident in your pictures, and for that reason, you may have the only possible routing, but the clamp on the engine mount is worth investgating, I think.

Scott Hersha · #10 03-10-2010, 06:40 AM

Sonny,
If you leave your fuel line where it is, you could use the longer version of the exhaust heat sheat shield. Spruce PN: 08-00051 ($19.85). It's 5" long.