Fuel Lines on a Rotax 503

Published by: Garrett Porter on 6th Mar 2018 | View all blogs by Garrett Porter

Yesterday I went out to my hangar after work, and during my preflight inspection, I found that my fuel line bypassing the bulb hand pump was completely broken in several spots and rock hard (this is the line between the fuel tank and the pulse driven fuel pump).  I am posting about it because it seems to have gone from functioning to obliterated in a very short time period.  I understand that fuel lines have a 5 year lifetime but I have also read folks recommending to change them every year, and even others saying that they go beyond 5 years before replacement.  I have already ordered a new hose to replace the failed one but I noticed that three options are out there.  Does anyone know of any reason to go with one over the other, other than price? Also, has anyone had an issues with their fuel lines or experienced anything similar? 

1. https://www.cps-parts.com/catalog/eppages/rotaxhosereplace.php?clickkey=3763

(This is the hose I originally bought and it is not actually fuel line)

CPS Hose

2. http://www.aircraftspruce.com/pages/ap/fuel_line/bingfuel.php

Bing Hose

3. http://www.aircraftspruce.com/pages/ap/fuel_line/fuelline.php

Polyurethane Hose


Here are some photos of the broken line on the aircraft:



A little background: This aircraft is a Pegasus with a Rotax 503 so the line interacts with fuel (including alcohol), oil, and air.  I live in Truckee, CA at 6,000' elevation where the Winter days are around freezing temp and Summer days see large temperature fluctuations between daytime and nighttime. I fly about twice a week typically.  I do not know how long it has been since this line was installed.



  • Damien B
    by Damien B 3 months ago
    >> Does anyone know of any reason to go with one over the other, other than price?

    I always like the see through blue fuel lines as it gave me a level of comfort being able to see the fuel in the lines. I always got it from CPS and got a few extra feet just in case.

    >> Also, has anyone had an issues with their fuel lines or experienced anything similar?

    I tried to change mine out when I had a 503 yearly. It was quite a cheap thing to do. When I had the Sabre trike, the fuel line entered the top of the tank and dropped in (I liked this style tank as the only opening was in the top so chances for leaks due to plugging the tank from the bottom were slimmer I felt). I would remove and do that line inside the tank as well. basically every line that could change was changed. Also the Mikuni Fuel Pump rebuild as well, that was cheap and easy to do, and the Primer Pump too, they can fail.

    I do know of one student whos fuel lines where clamped on too tight to the Mikumi Fuel pump and when you jiggled the line fuel came out of the cracks so be careful of going too tight with the clamps.

    I never had an issue with Ethanol in the fuel. I am at 5,834 elevation so the same temp range as you most likely.


  • Frank Dempsey
    by Frank Dempsey 3 months ago
    I use automotive black high pressure fuel line up to the fuel filter, then Lockwood purchased blue line from there to the carbs which lets you see air bubbles if they appear. So minimize the blue line as much as you can. Get the clear pulse (harder) line from Lockwood. CPS will send you the clear (soft) line for the pulse line. I think the parts guy doesn't understand the difference. Also, when you use plastic tube on plastic fittings, use a plastic clamp. Plastic on metal you can use a metal clamp. As far as the diaphram pumps, get a new one. It's an inexpensive part. Pay the extra 15 bucks. I used to rebuild them but the last one leaked because the cheap aluminum they use loses its flatness over time and they leak. Not a good thing. My 2C
  • Paul Hamilton
    by Paul Hamilton 3 months ago
    I like the blue lines because you can see the fuel but trash those hose clamps for the blue hoses - they are not round for the small diameters and can cause air leakage into the system.
  • jeff trike
    by jeff trike 3 months ago
    instead of clamps for the blue fuel lines, I use a double wrap of safety wire, then twisted off as usual to secure.
  • Gregg Ludwig
    by Gregg Ludwig 3 months ago
    Garrett, number 1 pictured is not fuel line, not intended for fuel line and not sold as fuel line. #1 is "rubber hose" sold as replacement tubing for the CarbMate (TS-111) instrument used to synchronize carburetors.
  • Paul Hamilton
    by Paul Hamilton 3 months ago
    I was never a fan of the safety wire clamp/attachment but now I also feel it is one of the best options for the blue lines.
  • Ted  Bailey
    by Ted Bailey 3 months ago
    Blue or yellow as long as it is alcohol resistant and for the last few years we have been using a zip tie designed for fuel lines, they work great and are easy to install. I like a black rubber fuel line only for the primer bulb bypass.
  • Doug Smith
    by Doug Smith 3 months ago
    My 2 cents after many attempts at the colored fuel lines. For a long time, I also thought the clear blue visibility was helpful. I even found Red at a hot rod supplier here in LA to match my trikes color. But after more than a few replacements of dried cracking hoses, I have switched over to good old black fuel hose. You know, fuel actually goes through it just the same. The air bubbles and dirt I thought I was looking out for are not there either. I have 2 fuel filters that are doing their job. Even if, the injector filter failed, the engine performance would tell me what’s going on before you actually see something in the line.
  • Garrett Porter
    by Garrett Porter 3 months ago
    @Gregg Ludwig
    Thank you so much for pointing this out. It came up when I searched "fuel hose" and in the description it said "High quality "santoprene" fuel and oil resistant hose" which led me to believe I was onto the right item. I see where I screwed up though. Luckily a friend has some extra of the correct blue fuel line to get me going again soon.

    Thank you all for all of these suggestions. For this year, my plan is just to replace the blue hoses with new ones (the correct kind) and to use either zip ties or safety wire to secure them as suggested by most folks. Based on how long the blue lines last before needing to be replaced will decide if I go black lines after that or not.
  • Frank Dempsey
    by Frank Dempsey 3 months ago
    Fuel Filters - I used to use these small glass filters with a metal screen on my 912 in the past. They can get dirty faster than a larger filter because of the small area so I switched to a large area filter after having one leak on me. I'm wondering whether an oversized filter could cause a hard start in cold temperatures for lack of fuel. I can see that the large filter has some air in it all the time. I've noticed that the new Apollo 912S trikes (like mine) now come with the small AutoZone Glass filters.
  • Doug Boyle
    by Doug Boyle 1 month ago
    When using the glass filters try and find the metal nipples vs the nylon ones. I've seen the nylon ones develop leaks/cracks. I think Napa sells the ones with metal nipples. Also, the blue line should be switched every 1-2 years; I sold my 582 but would experiment with the yellow line (Tygon?) for less cracking/leaking problems next time.
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