Hi all! I have a question here that is bugging me to no end. I have a 1976 455 LaSabre engine installed in a 55 Buick. My head scratching amounts to this. The mechanical fuel pump has three fittings and/or connections if you will. One, fuel in, two fuel out, and the third is a straight down tube with a very small hole at the bottom. What is the third fitting for??
Vapor return. It circulates hot fuel and vapor back to the fuel tank to keep the fuel in the pump cooler. It fights vapor lock. If you block it off, the pump will make a bit more pressure. When I was running the stock pump, I installed a ball valve in the line so I could shut it off when I was racing.
Thanks to Bruno and Larry for answering a puzzling question. Interesting story goes with that. Last September I replaced the pump (flat out died). Well..........about a 2 weeks ago, the pump starting spitting fuel from this outlet (I do not have a return line to the stock 55 tank). So.......in my distorted way of thinking I assume the diaphragm is taking a dump, since the amount of fuel spitting out on my commute back home was pretty significant. Out comes the old pump and in goes a new one. Started The Beast up and whoa!!!! Fuel is streaming from this third fitting. Now the confusing part for me is that the old pump never acted in such a manner until the aforementioned. In my infinite wisdom..............I assume (once again) that I just bought a piece of foreign junk. So..................off comes the pump..........pick up my refund and head north to the Canadian border (online that is) and order another. Well Hells Bells if the new one doesn't do just what the other did. So scratching my monks head..........I start remembering the 70's, EPA, fuel (sic) efficiency etc. Ah! Block it off. So that's just what I did. Car runs fine. That doesn't mean that I was not checking the oil for trace amounts of fuel. Some old school things just never go away. Moral to the story............. Never assume you have all the answers. Ask around. Nothing ventured nothing gained. To Larry...............I would think The Beast would go a tad faster if I had your setup:3gears: Again..........thanks to all:grin:
