Actually, not so much on a 4160. It just has no secondary accelerator pumps and the vacuum control merely allows the throttle mechanism to engage the secondary throttle plate when conditions are "right" . There is NO secondary metering plate, per se, on a 4160, as the 4150 has. Totally different animal to tune. But YES, Correct on Vacuum drawing the fuel, but so is the 4150. So many HATE the 4160 and declare the 4150 the "way to go" it drives me crazy.
Post some pics of what you have. I kinda had this on Pickle when I first bought it. Turns out, the, well, whats a good polite word for "jackass"?.........anyway, mounted a screw into the mechanism to make it act like a "mechanical secondary" Seen this mod on the net as well. Not a good idea.
4150's have their place. 4160's do as well. Sounds to me, and just thinking out loud from reading this a few times, That it is either a carb linkage problem, as Electrowoman pointed out, not allowing the carb to return to "idle" or "reset" state, OR a needle seat problem. Not much else can cause secondary problems on a 4160, short of warped bowls, throttle plates, vacuum leaks, etc. The normal crap we deal with on any of the Holley's.
Please get this, that BOTH the 4150 (Double Pumper) and the 4160 HAVE primary accelerator pumps. What they do is when the throttle is Mashed, off or near idle, or "hit aggressiveley" is dump a bunch of fuel in nearly immediately. The 4150 has the ability to do this even on the mechanically operated secondaries (Meaning it CAN do both at the same time, if necessary). The 4160 does not have this ability. The metering blocks on a 4150 are there to SPECIFICALLY measure and meter fuel on both ends of the carb. Not all four corners, that's what a Dominator does. Why the 4150 requires a LOT of plug reading, and tuning.
4160 works on a VERY different principle. Secondarys can ONLY open, controlled by the diaphragm and spring, when vacuum is where you want it. The butterflys will then open relative to throttle position, BUT fuel will only be introduced as vacuum says it's necessary, based on the spring used on the secondaries (Hopefully set up after a few plug readings), the jets used, and vacuum available.
Understand that under a mashed and held full throttle, a 4150 acts the exact same way as a 4160 after the first few seconds. Fuel will NOT be pulled from either bowl unless vacuum exists to suck it out. The accelerator pumps only exist for increasing throttle position changes. No matter how quickly. Yes, the 4150 shines from idle to balls out, because it has two, can open the secondaries imeediately, and...........IF the engine vacuum supports it.........suck the fuel from both bowls. The Dominator does the same thing, but on all four corners being able to be tuned independantly.
Long way around your problem, but you got something leaking from the carb Needle/seat area is where I'd be looking on the secondary side. Could be warped bowl, warped or bent main housing. Could actually just be an old Nitrophyl float so soaked it never actually floats and holds the needle open all the time.
Ray
