Feul pump and filter questions

[Alk-3]

I'm having bit of a vapor lock issue (I think), similar to what's being discussed in another thread. The truck starts up fine, first crank every time when cold, but if I leave it sit for ten minutes or more it becomes hard to start. I have to crank it for 10 seconds with the pedal on the floor and then it will finally start, and send out a small cloud of smoke.
I wonder if it's a vapor lock issue, and so I've watched the clear fuel filter and there seems to be some air bubbles coming up from the pump.
i have an electric pump as well as the original mechanical pump installed, and have them both running. I would like to take the mechanical pump out of the equation.
can I just bypass the pump with a new line, and let the pump just stay attached to the engine? Is there a proper way to remove the original mechanical pump from the system?
secondly, I want to put a return line back to the tank from the fuel filter. I will buy a filter with two outputs, and one input, but is it as simple as running a line from the pump to the inlet of the filter, and then running one outlet line back to the tank, and the other outlet line to the carb? Should the filter be as close to the carp as possible?

[gudjeon]

Mechanical pump can just be left or make a blanking plate to cover the hole in the crankcase. Using two together is not a good idea anyway as a a diaphram failure of the mechanical can have the electric one pump the crankcase full of fuel. or not work becase air is sucked in before the electric pump. Electric pump made for low pressure and return line works a treat. No vapour lock and easy starting when its hot. Modern fuel is not stable in an open carb system. I used a 80's Chrysler vintage fuel filter and made a bypass hose back to the tank. Fuel is kept cool and constantly filtered as a bonus.

[Alk-3]

Perfect, this is what I was hoping.
I have never used the electric pump until yesterday. One of the previous owners put it on, but it was disconnected when I got the truck. I will disconnect it until I get the mechanical one bypassed properly.

[J!m]

Although there is a risk of running fuel into the crankcase if the mechanical pump fails, I have used them in the way yours is set up with a high-flow pump in a high-horsepower application. The (over sized) electric pump and large Fram fuel filter (that looks like a small remote oil filter) sit at the tank and push the fuel up to the mechanical pump at the engine. The mechanical pump then acts as a 'regulator' so you don't flow too much fuel to the carb which may get past the needle valve.

This works very well and thee are no starvation problems ever.

Loop systems:
If you return the excess fuel to the tank at the filter, you may actually set up a slight vacuum at the carburettor that will prevent proper fuel flow. If you are planning on a modern loop-type fuel system, you should flow through the filter to a banjo bolt with two fittings right on the carb, and run a smaller diameter return line than the feed line. This ensures a slight restriction at the banjo bolt so that fuel is always available at the carb. If there is less resistance back to the tank than into the carb, you know where the fuel will go... This is how the 'factory' does it these days, although they keep a fuel rail filled at high pressure for injectors. You may be able to find the banjo bolt you need at the scrap yard off a 'newer' carburetted car. If the fittings are the same size on your found bolt, use a brass tubing reducer barb to reduce it somewhere before the tank, or worst case (with best adjust-ability) install a needle valve in the return line to get the restriction.

Set up can be a bit tricky as you have to determine you have enough fuel available at WOT yet the pressure is low enough that it does not get by the needle valve at idle. This can be the true cause of 'loss of power' cruising on the highway, and not simply the anemic engine... Get a low-pressure high flow fuel pump. Carter pumps are the brand I relied on for the big cars.

[gudjeon]

The bypass filter has a small brass orifice to restrict fuel flow on the return line and it is a 1/4" dia, versus the main 5/16" dia fuel line so it has a built in flow restriction. It is made of metal ta' boot. Once shut off, no pressure is left on the needle and seat. Also heat soak will not have gasoline expand and flood the engine silly.

[J!m]

Sounds good!

But you said it is metal, so you don't se when it is clogged up. The way I suggested allows the use of any filter (from any part of the world) and those details I try to keep in mind with my Rover mods.

For a grocery-getter, it soulds like the simplist way to do the loop mod!