Type Half Fuel Pump
For additional information on this topic see VW Type 1 & 2 Fuel Pump.
Using Pulse Pumps
Pulse style pumps by several manufactures may be used. These are the same type that is used on snow machines. Based on the information provided by Mosler, it is uncertain whether taping into the crankcase venting is a good idea. It may be possible to safely do this by using a snubber valve between the case and pump. (A snubber valve is simply a piece of metal with a restricting orifice of proper size.)
The Mosler manual mentions the use of the Mikuni pump if necessary, but says it should NOT be connected to the crankcase vent; instead connect it to the intake manifold. They feel the crankcase develops far too much pressure. The Mosler manual also says a pressure regulator must be used, set at no more than 3 psi. You can buy a new Mikkuni clone fuel pump for about $18 on ebay.
Fuel Flow Required
At the time of this writing an attempt was made to varify what models of pumps would provide the satisfactory GPH fuel flow for VW's but no specs or information could be found. It is estimated maximum takeoff fuel flow of 4-5gph for 1/2-VW's and 7-9gph for 4cyl-VW's would be needed.
An accepted rule of thumb for using SFC (spacific fuel consuption) is to multiply horsepower by .10 (naturally-aspirated motors) or .12 (force-induction motors) to come up with a fairly accurate guide to how many quarts per hour of fuel you will need to feed the engine..."
A 2300cc VW at full throttle might get 100hp * 0.10 = 10gph
and economy cruise might be 50hp * 0.10 = 5gph
Mikuni says to keep the pulse line under 13". Make sure you use tubing that is rated for vacuum or is designed so it will not collapse.
The recommneded tubing is thick wall polyurethane tubing sold as "pulse line" from the aircraft suppliers. Blue urethane fuel line has good resistance to damage from hose clamps, but has a very short lifespan in hot climates with direct sun and heat.
Braided 1/4" vinyl tubing works well if it's not too long, but it's not as stiff as the pulse line. But the gasoline WILL attack it eventually; vinyl tubing is NOT nearly as resistant as the red plastic gas tank which is made of polyethylene. Vinyl tubing should not be used for fuel unless it's specifically formulated as fuel line (like the yellow Tygon) and even then it only lasts a couple of years before needing to be replaced.
Another option that has been prooven to work well is automotive Fuel Injection line. While it is designed for high pressure it is also designed to hold up to the blended fuels so will not breakdown or come apart.
Facet Cube Style 12 Volt Fuel Pumps rated at 15gph (40106, 40108, 60304, etc) are available at any desiried pressure and cost about $50. 10gph inline pumps (477060 are about $100.