80 jets in the sec is to big. What is the PV in the sec? Have you checked to see if the gas pedal actually opens both butterflies completely? Many never do, they just assume. Read old school books, Alex Walordy's "Super Tuning Holley Carburetors" and Dave Emanuel "Super Tuning and Modifying Holley Carburetors".
I have considered that I might have a vacuum leak, but in my opinion that normally requires a much bigger primary jet and idle screws backed out dramatically to run, I run 66 in the primaries and my idle screws are out a turn and a half. What kind of vacuum leak only shows up at 30% throttle? I do not run a vacuum advance distributor, mechanical only - supposed to be a turbo car eventually. I did pull the plugs and none seemed oil fouled from an internal intake manifold leak. The PCV is also new and seems to be functioning properly. I was surprised by how strong of a vacuum signal I was getting at cruise (15-17.5 inches) and my lean condition starts right under 10 inches and goes away as soon as I hit my PV opening at 6 inches. Wouldn't high vacuum negate the possibility of a vacuum leak? I am just wondering, I am not that well versed. I do have to say that I am getting suspicious of my ignition system, I backed off my total timing when I noticed the lean condition until I solved it because the combination of a good amount of timing and lean AFR seemed like a bad recipe. I am running 10 initial and 31 total with light blue springs. I agree that the 80 is too bit, that's what the carb came with and I haven't touched it because I don't care about running rich at WOT, at least not until I solve my lean condition, I will probably to down to a 76 or 75. No power valve on the back metering block. And yes, I did check that the butterflies open all the way with the gas pedal.
This might sound dumb, but would scavenging affect carburetor signal dramatically? I do run full length smallish diameter headers (1 5/8) and a 2.5 inch x pipe exhaust, both of which are supposed to promote scavenging. I also run a tight quench .040 and AFR heads have a pretty effective combustion chamber and I am wondering (maybe foolishly) how much that plays into my carburetor tuning. The air velocity through both my exhaust and my intake should be pretty high right?
Good news guys, put the 8.5 valve in and it is much cleaner at part throttle, AFR starts at 13.5 and falls to 12.5 and stays around there. I retorqued my intake manifold and carburetor one more time and I do have to say that with the engine hot and thermal expansion doing its thing I could easily turn the bolts and extra 1/8 to 3/16 of a turn - I just torque them to whatever my wrist can turn over the head of the ratchet. I also torqued the carburetor down evenly. I plan on advancing my initial timing to about 14 which will raise my idle and allow me to use up less of the transfer slot and I am hoping it will change the behavior of the accelerator pump some as well and maybe get me back down to a 30cc pump.
After you get off idle, that t-slot is your friend until the booster kicks in, so having all of it available is good. Sounds like that 8.5 power valve is giving you that missing enrichment though. I am going to remember the vac gauge usefulness should this haunt me in the future. Let us know of anything else you do to dial it in. Your info is of particular interest since you got that snazzy AFR gauge, lol.
With valve now installed, it does if vac below 8.5". A good crack of the throttle at low RPM will drop vac even lower.
With 388 cubes and 238* cam I doubt he's below 8.5 inches of vacuum at part throttle. If he is, he has other problems.
Well guys I am doing a rare thing here, giving you an update: the Maverick runs like a champ and my carburetor problems have been fixed. There were multiple issues at play and it took me a hot minute to wrap my head around all of them. First of all the fuel bowl level was too high, at the very bottom of the sight glass is where it is happy, not the middle. Second, the primaries I ended up going with were 69, I was having an issue with the accelerator pump discharge nozzle being drawn on and it would add fuel at random events, sometimes idle, sometimes cruise and it was throwing off my AFR constantly at random times, I would make a change and from one moment to the next it would do two completely different things. My cruise AFR is 13.8 and I might lean it out some more in the future. I did have to drill out my power valve circuit restrictor to compensate for the smallish mains and to keep the jets “square” on all four corners. The power valve size didn’t affect my part throttle AFR as much as drilling out the restrictor did, so I ended up with a 8.5” valve and my AFR never goes above 15:1 at tip in and through a pull. WOT is 12.3-12.7 and my secondary jets are 80s.
