Fuel Recirculation

[Jim Fierst]

I know there are some postitive benifits about recirculating fuel but I wonder why Lancia did it on carbed cars? I know there was a 'fix ' on the 79 carbed Zag's to cool the carb but they already had the recirculation in place so it wasn't preventing vapor lock. I seem to remember my Scorpion had a return system as well and I used it when I converted to dual DCNF's. The t enginei am building for the LBZ will have dual DCNF's and I will probably use the recirculation feature. I am just wondering if it is really needed or not.

[Will]

It limits pump overpressure, Jim. On the Scorpion, there's one other interesting bit- the pump impeller and motor are magnetically couple so the (stock) pump won't go over 4.5PSI. I did a windshield washer fluid column test with a long pole, and the Scorpion pump therefore doesn't need the return line- or an external FPR.

Recirculating the fuel generally keeps the supply line cooler and thus the fuel, with obvious benefits in terms of det control- the answer to whether it is needed in your application depends on whether your pump- whatever you are using- needs it in order to keep from overpressuring your carbs.

I'd personally make the decision you did and retain it as beneficial, even if not necessary.

[SubGothius]

I seem to recall recently someone here had described a sort of shallow "cup" fixed to the bottom of the tank, into which the fuel pickup dips -- and the return line outlet as well (I presume) -- which prevents the pickup from immediately sucking fumes from a low tank during hard turning. If so, the return line would also keep that cup full.

BTW, when I recently replaced my fuel pump (much easier than on a FI car!), I discovered that a PO had disconnected and capped off my car's fuel return line! However, with that and also an inoperable carb-cooling fan, I can't say vapor lock has been a significant problem, even during the blazing-hot summers here in Tucson, perhaps the occasional warm-restart reluctance now that I think of it.