Return line for big 4 conversion ??

[PrestonH22]

I am rebuilding a 1974 914 with a 2.7 liter 4 cylinder engine with dual weber 44's.
Is there any benefit to running a fuel return line (carb to fuel tank) with this setup.

If so what will I need to make a return line work?

[tailwind22]

If you google search 914 fuel line routing with carbs you will find a lot of conversation and a split jury on whether to do a return line. I put a Raby 2270 big 4 in my 914 a year ago and elected not to do the return line and I have not had issues. If I recall the main reason to do a return line was to not have slow moving fuel in the line not overheat in really hot weather. When I researched the topic there were different suggested routing diagrams out there if that is what you decided to do. Others with more practical experience then myself may weigh in.

[John Rogers]

For a while I had a 2.8L four in my vintage race car and we never used a return line. I did have a fuel pressure regulator and also a gauge and if I remember correctly there was about 4# of pressure at the carbs.

[GregAmy]

Cars generally have return lines when they use high-pressure fuel and pressure regulators bypass the fuel to a return line.

However, carbs use such a low pressure fuel and pumps (3-5psi) that can be effectively regulated with a simple valve.

One can argue that blowing off your fuel pressure at the engine compartment back to the fuel tank would go a long way toward reducing chances for vapor lock. However, one can as easily argue that vapor lock generally happens after stopping the hot engine, when the now-no-longer-moving fuel will percolate in the lines in the engine compartment...then one counters that by pointing out that the now-percolated fuel will be purged back to the fuel tank by the bypass system once the key is again turned back on.

I personally don't think a return line is needed for carbs except in extreme cases. However, did the factory use a return line on the carb-equipped 914-6? If so, I'd replicate it. If not, I'd not bother to add it.

[Fly Mach .86]

I have a 2.2 liter type IV with 44idf's for the last 15 years. No return line and never a problem with vapor lock. And my fuel pump is in the engine compartment.