For what it's worth, here's the current state of the spark plugs. This is with easy, light foot, driving. Fully warmed up, no hard acceleration, staying out of the power valve, etc.
Also, this is one jet size down from the stock setting, which is Holley "spec" for my altitude.



A couple of them are turned so the white is showing for contrast, but they're all about the same color. The dark areas aren't shadows.


.

 

Well, the replacement showed up today.
The first thing I noticed is that they sent me a new one and not a refurbished one. It came in a standard Holley box (instead of a regular brown cardboard one). The date code says it was made on September 8th, 2013. Last month! The power valve had the size laser ink printed on the front (luxuriously easy to read in comparison to any other I've seen) instead of embossed into the metal, and the accelerator pump cam was made out of a different material than I've seen before. Completely flat and opaque in color vs. the semi translucent ones I'm accustomed to.
Not that any of it matters, it just looked very, very new. That and everything inside was filled with some kind of cleaner/oil that I'm assuming is to keep it all fresh while sitting on the shelf.

The other strange thing I noticed is it came with 64s again. ??? Holley documentation, and the tech I've spoken with, both firmly say it's supposed to come with 62s. They even sent me a new package of jets to make up for it. So why is a new one, again, coming with 64s? Very strange. I'll ask them about it though.

Installed it this afternoon, and it fired right up and idled nicely. The pop in the exhaust is much less, to non-existent. Seems to be a much tighter carb.
I didn't really have any drivability problems with the first one, but hopefully this one will fix whatever issue was draining my gas. I'm getting horrendous gas mileage. Driving with a baby foot, I've gone 170 miles on around 17 - 19 gallons (not sure exactly until I fill it).

As the pic of the spark plugs above showed, it was at least running really rich, so at least there's a reason.

 

How nice they sent you a new one! I hope this one works much better for you and produces pleasing mpg results.

What I thought would be very educational for both of us would be to try that carb on both the DP and then your engine with the C type manifold, using the open plenum type adapter. I understand the vehicles have different gearing, but it may be educational.

 

Trying different things is the only way to find out how one thing works to the next thing...and is educational.

 

I've thought about trying the carb on the other intake. I might give it a shot out of curiosity once I get it sorted out on this one.

Well, the tech guy said they've actually changed the jet size in that carb and 64s are now the correct size. I wonder why. That's the same jet size as the square bore with a much smaller venturi.

 

The venturi may be smaller, but the amount of air moving through them is the same, and all that air needs fuel metered to it. Albeit, the smaller venturi means the air moving through it is moving faster and should therefore being atomizing the fuel better. That means I'm looking for major mpg here, dude.

Only a AFR gauge will tell the accurate tale. Good luck.

 

Changes happen without any particularly satisfying explanation. They might have run out of 62s on that day...at any rate, whatever the carb comes with is the starting point and not necessarily the end.

 

I'm still curious why a smaller venturi would still have larger jets (not necessarily 62 vs 64). The 390 was smaller venturis and it had size 52s. I would think that it would be proportional to the venturi size. The 650 CFM obviously comes from the massive floodgates on the back end. Dunno, though.

Either way, had some interesting findings.

First, is that I had my first interstate experience since I put it on. I held 65 for about 4 or 5 miles, and on average, my hg at cruise was a good 2 - 3 higher than it's ever been. Normally, it's 9 - 11 depending on the grade, and it was an average of 11 - 14. I haven't ever seen that. I boosted up to 75, and it averaged 10 - 12 in cruise. That definitely should mean good things.

Out of curiosity, when I got home, I let it cool and popped another spark plug.



It's "healthy" and all, but still a really dark burn. So, out of curiosity, I decided to swap out the 61s I had in there for the smallest jets I had on hand, which were size 58s (4 sizes smaller than documented, 6 sizes smaller than what they're shipping them with now). Took it for a spin and it drove no different! I even tried several runs of letting it get down to around 1000 to 1400 RPMs and putting my foot to the floor. Normal experience has told me that too lean of jetting and it would fall flat on its face, but no. It just took off and started accelerating like there was nothing wrong.
If anything, overall, it may have been a tad crisper.

Pulled a spark plug when I got home... still dark.

I'm not sure what to think at the moment.

 

AB--there were a few things I wanted to mention. I read that plugs don't color to the use right away. They need a few hundred miles. Also, I'm looking at those plugs, and in the photos it may be difficult to tell. They look new, but they don't look bad.

I'm not surprised you are finding the oem jetting rich or unneeded. That carb is replacement for a v8, is it not? That explains it. Let me illustrate my point by saying that while I was doing QJ's, I pulled three off sbc's, 327's or 350's. All those had right around 72 jets with 43 or 44 metering rods, all about .030 difference.

Then I got a QJ on ebay out of a 305 (iirc) pontiac. That, I found, had 72 jets with 52 rods, a difference of .020, and oem in the book. It doesn't/ didn't mean it ran leaner, but that a smaller engine required less fuel (along with less air entering) to be metered. That was a lesson for me. Good luck. You have to get an AFR gauge.

 

Ah, that may be. I thought that it only took a few miles to do so.
The plugs are about a year old, and I agree they don't look bad at all. It's a good, healthy burn. Just really dark. I've heard with today's fuels, you can almost get away with a perfectly clean plug. My other 300 with the square bore on it has a nice light tan spot, so a spot as dark as I'm getting is telling me that a lot of extra fuel is flowing through. Just means I can lean it out.

Here's a pic I found of a healthy burn, for comparison. Just a nice, gentle tan:



I thought jetting wasn't related to engine size, just the carb itself. A 600cfm Holley on a 300 six needs the same jetting as one on a 400 V8. The accel pump and stuff is how you tailor it for the engine. At least that's my understanding.

Either way, it seems quite happy with the 58s. Just a slight lean accel here and there which I might be able to fix by upping it a notch to a 59.

Definitely want a wideband. I take it you're liking yours.

 

I was wrong. I went and read an article on carb adjustment. I guess newish plugs color quickly. I'm never sure about what I read online.

I love my AFR gauge. If I turn a mix screw a fraction, I see the result on the gauge. It is amazing. k

 

Hi Guys..along these lines, I remember recently jetting a 1.01V 2100 with 42's..and it ran fine,(on another Ford product) just "slightly lean, switched to "44's" and for that venturi size, found the sweet spot, just out'a the power valve and a clean exhasut pipe..

At least with a carb YOU have choices..not like the situation where a pewter makes the decisions...carry on.

 

Hey John, out of curiosity, what were the stock/original sizes for those carbs? I'm curious how much of a change you made for both.

Isn't it great finding the sweet spot on a carb? It's a fun, fun feeling.



Well, been driving around now for 2 days with the 58s in there. I can finally see what people mean by dropping 2 sizes for gas mileage, increasing 2 sizes for power. I can feel less power with this size, but that in no way means a lack of drivability. Just less power. It accelerates great, responds great, and is nice and snappy. Just...not as OOMPHY.

Before, whenever I did that, I'd kill all the drivability, and every time I'd hit the gas, it's like someone gut punched it and it'd fall flat on its face. I got so tired of it. Kinda cool having a carb that responds to jet size changes correctly.

If the gas mileage numbers improve (which I'm sure they will with six drops in jet sizes), this is definitely the best carb I've had. I love driving it every day and I feel like I've finally found The Carb. Just need some better mpg numbers to make me feel like I'm not paying out of the nose for it.

 

I you're asking about the 101-102 2100's, I've seen mostly 44's-49's generally.

Good 2 hear ur happy with your carb..Even thought the search is fun..experimenting with what you like is even funner..

Keep the faith!..

 

Hey AB, quick question: which NP435 are you running in your bronco? Are you running the wide ratio or close ratio?


sorry for the slight thread hijack