<VV> Single Carburetor

[Mike McCrae]

This was my letter to “Corsa “ RE: use of single carbs....perhaps there are some words in there that may help with your problem....
Regards, Mike McCrae

09/08/2010



Dear Larry,

I found the four barrel manifold article interesting, but what always gets me is that no one, VW, GM, etc. has ever made a remote carb work well without applying heat to the manifold. Remember the Grand National....they had to plumb the turbo intake manifold to accept heated water from the radiator. There is a very simple answer which I provide, and solves these problems. The bottom of the four barrel intake manifold is machined away, and an aluminum box is fabricated and tig welded in place to carry engine oil. The oil comes from the oil filter log which I machine off....A remote filter is then used on the return line from the heater box. This system not only heats the plenum, it cools the oil as well. The oil leaving the manifold is generally 10-12* cooler.

Exhaust could be used for heat if one wants to replumb an AIR exhaust manifold. The perfect example is the single carburetor V W engine. 

 All carburetors become refrigeration systems, due to the Fuel/Air (F/A) compression in the venturi and idle systems and later expansion in the plenum. All modern engines compensate for this phenomenon by locating the carburetors over the oil valley in a V-8-6, or over an exhaust manifold in inline engines. Corvair engineers wisely mated the intake manifolds directly to the head, keeping the F/A mixture warm, and in suspension.  The lack of heat to the remote 4-barrel manifolds we use allows the F/A mixture to condense on the sides of the frozen plenum, creating a very lean situation, and resultant hesitation (lean skips). Winter operation becomes almost impossible due to carburetor ice formation with resultant frozen idle circuits. Most folks compensate for the problem by using the 50 cc accelerator pump and fire-hose nozzles. The result being poor gas mileage and extreme dilution of the oil at the top compression ring. With my system, one can use the stock Holley accelerator pump and normal nozzles.

My suggestion for initial carburetor settings in the Holley 390, 4160 series is as follows:



Stock accelerator pump (NOT the 50cc)

.031 Accelerator pump nozzles

.057 primary jets

.059 Secondary plate jets

75 power valve

Electric choke

Purple secondary diaphragm springs





Best wishes, Mike McCrae

619-466-0014