351C where to start?

[boilermaster]

351mach1,
It appears that basstrix and I are a little bit at odds on your main jet tuning.
I would have you richen up the main jet and lean the PVRC (which in your case ,may be a fixed jet)
and not easily be replaced, you may have to compromise here.
A lot of this may depend on where you live, I see you are in Vegas, basstrix in in Arizona and I am in Michigan @ 600ft. above sea level and have nothing to compare that to.
You are too rich at WOT, but your cruise is a tad lean for my liking here in Michigan where my humidity
is WAY different than the both of you.
Time and testing is the only answer.
Boilermaster

 

[351mach1]

You guys are priceless!

I will say that if I can get this tuned "good enough" that that will be good enough for now. I purchased this carb before I really knew anything and it was the cheapest one available. I do plan on changing rear gears, swapping to a manual transmission, and then upping the power of the motor so I imagine I will be changing the carb to a 700 cfm double pumper when I get around to the rest of the mods.

This has been an incredible (albeit frustrating) deep dive and learning experience into the holley carb!

 

[basstrix]

My reasoning is the following: Your HS cruise numbers are 13.5 and 14. HS cruise is primarily controlled by the HS circuit (main jet & HS air bleed) with a small contribution from the idle circuit. This AFR won't get you the best MPG, but it's not bad. The WOT numbers are 11, 12, and 13.....all over the place. The 12 and 13 numbers are not bad, but the 11 is rich. Let's assume you're OK with the HS cruise numbers, the only alternative to leaning out the WOT without affecting the cruise number is to lean out the PVCR (power valve channel restrictor). That's best accomplished with a tunable metering block and smaller PVCR jets. Alternatively, you could optimize the HS cruise by dropping 1-3 jet sizes, bring your HS cruise to 14.5-15...this would drop the WOT number by some amount and get you closer on that end w/o getting into the metering block.

@boilermaster: From my experience, if the main jets are increased, the HS cruise AFR will go richer. IMO, he's already a little rich at that condition. I agree on leaning the PVCR's to get the AFR at wide open throttle where it needs to be.

My suggestion is to repeat your data collection...maybe record a video of your vacuum, RPM, and AFR so it can be reviewed. I would be lost w/o a data logger.

Make 4-5 WOT runs. Do a couple from a dead stop and run at least through 1 gear shift, 2 if possible and do a couple in 2nd gear starting from a 15-20mph roll.

Make 4-5 LS cruise runs. Keep the RPMs steady as possible and run at 2000 RPM

Make 4-5 HS cruise runs. Keep the RPMs steady. Do 2500, 2700, 3000. You can do these in 2nd gear, if needed.

EDIT: You need to duplicate the WOT runs with the secondaries disables so you can observe the contribution from each half of the carb. This is only needed for the WOT tune.

 

[basstrix]

Thinking about this, we haven't really talked at all about the secondary tuning....and for the WOT tune, this is very important. The easiest way I've found to assess the contribution from each half of the carb is to disable the secondaries and focus on what the primaries are contributing, then move on to the secondaries to bring them in tune.

Is your carb a 4150 (secondary metering block between main body and float bowl) or 4160 (float bowl directly connected to main body)? If you have a 4160, they are not as convenient to re-jet.

What about the secondary vacuum canister? Is it adjustable with a screw? I'm asking because we want to disable the secondaries for a few WOT runs and see what the AFR is. If it has the screw, you just close that up to disable.....if not, then I use a piece of wire about like what's inside a bread bag tie.....and tie from the slot on the left side of secondary throttle shaft to the nearby bolt holding the carb down. The wire needs to be nice and tight.

When the secondaries are disabled, you'll get a little bit richer AFR than if the secondaries were open, so just be aware.....from memory, I tend to see 1/2 to 3/4's of an AFR point richer...but I can look at my data to give you an accurate number.

It may be that what's really needed is to lean the secondaries a little....but testing WOT with them disabled will tell that story.


EDIT: I found the link you posted for your carb model....4160, standard type of secondary pod. You can either disconnect the secondary diaphragm (I don't like doing this, the throttle could open and cause a runaway condition), or wire them shut, to disable. I made a quick picture to show what I mean. I took a fender washer and drilled an offset hole for the wire, but you can wrap it around the stud.

 

[boilermaster]

Was wondering when this can was going to get opened.
I really like the QFT-63-1 vacuum pod with the screw adjustment, additionally, I use a small hitch pin clip on the rod to housing to tell what rpm I am actually starting to open the rears.
agreed that there may be an opportunity to lean this by opening the rears just short of a lean bog.
Guessing Holley has a black spring in there now.
hitch pin clip works way better than a paper clip.
Boilermaster

 

[351mach1]

I realized I misspoke in an earlier post. You are correct that I have a 4160 with out a metering block. I will go ahead and order some smaller jets as well and find a day to do all of the above. I don't have a data logger but that's what the girlfriend is for