I wonder if my fuel pressure is too high at 8 psi. Either way, its a single plane manifold on a 496 making 7-8" of vacuum at a 1000 rpm idle. What am I missing? Apparently the stock jetting of 80/80 should be very close, but it appears to be quite far off. I'm going to go with Larry's approach of finding the right primary jetting to get a 13.5-14.5 cruise, and go from there
I also have a very restrictive air filter on the carb right now. I think I'll continue to tune the car with the air filter off and just use the hood scoop for cooler air
Secure the base of the air cleaner to it if you're going to do it that way. That'll affect the flow into the carb.
Are you sure of the vacuum level? Have you monitored vacuum while driving the car? That's where I would start.
Well, I can’t go lower on power valve. Vacuum has no effect on part throttle cruise, unless my cruise rpm somehow generates less than 3.5” of vacuum. What I can’t understand is how I have two opposites. A rich cruise and a lean WOT
Drive the car and extend the vacuum gauge into the car. Write down the cruise vacuum, and how it changes as you progressively open the throttle. You might be surprised at what you'll see.
The a/f bung is in the reducer off header, up from centerline? Readings seem wacky. Maybe clean the sensor.
You need to check your vaccum like Larry said. At cruise, at light then moderate acceleration and the at WOT. Running a power valve that small there may be a chance it is not opening soon enough or at all. You may still have vaccum at WOT. Not to get in a pissing match but I found what worked for me to select a power valve was taking my highest steady cruise vaccum and divide by 2 (starting point). I know Holley wants half idle vacuum. I tried that and it made me go a bit lean and slightly stumble When accelerating briskly at highway speeds on the primaries. The Holley method gave me a 6.5. Checking vaccum when going lean, I observed about 9 inches of vaccum. This means my 6.5 was not opened so it was no help. So the method I used with 21 inches at 65mph landed me at 10.5 power valve. Solved my issue. It opened sooner when my engine wanted it. I always read that high power valve openings are for high vaccum cars like stockers and lower power valves are for "high performance". But some folks forget that the different valves open earlier or later. Hope you get to the bottom of it.
Ran 74/94 6.5 power valve. Still 12:1 cruise, but as I got into the throttle, it would go dead lean. Dead lean at WOT Ran 82/94 6.5 not much better, 11:1 part throttle. Still somehow dead lean at WOT. What is happening? I can’t even get the WOT mixtures right. Even when you may expect the mixtures to be rich
That makes no sense at all. Either something is wrong with the AFR gauge/sensor or there is a major problem with that carburetor. Try a known good carburetor. Maybe you can borrow one for testing.
