Thread: Holly 4150 Tuning Problems

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I am running a new 427 Small block with a cam spec of 233/239 @.05 and .544/.55 lift. I ran a 650 Edlebrock performer carb for a while without any problems. I did have to drill the primary butterfly valves. In order to maintain about 10" vacuum I have to set the idle on both at about 1000 rpm. When I put into drive it drops to about 800. The holly seems to want to foul the first four plugs only (1,3,4 & 2) the rear four remain normal. Because the primary valves favor the first 4 cylinders, (dual plane) could I have them set to rich? My theory is air/fuel from the secondary is flowing through the fuel being drawn from the primary idle circut creating a rich mixture. When one of the rear 4 cylinders draw, they are pulling air/fuel from the secondaries but most of the fuel rich mixture from the primaries is falling out. Any tips?

Try running a hotter plug, one size . It should take care of your unburned fuel problem.

Is your primary power valve correct for that much cam? and what is your primary side jetting?

I had this problem and there can be two different problems. First and the easiest test is to check the fuel level in the front bowl. Take the screw out the side of the bowl, when the engine is shut off. If fuel comes out of the bowl you need to change the float level. The fuel level should just be at the bottom of the screw hole. The float level can be changed by loosening the top screw on the bowl and then adjusting the level with the nut. The second problem can be the power valve. The front power valve may not be sealing correctly or be broken. I would try to take of the metering block and make sure the power valve is tight. Mine was loose one time and the idle was completely rich. There needs to be a good seal or the power valve will leak and too much fuel will enter the engine. Also check to make sure the power valve is not stuck open. You can also use a vacuum gauge on it to test the opening point.

I could advise you to put the Edelbrock back on, but won't. Holleys are prone to warping the body when the float chamber bolts are overtightened. This lets fuel suck into the vacuum passage to the power valve, richening the primaries. A fine file and some finesse wil straighten the surface and fix the leak.