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I have been running dual, Carter W-1s for a couple years now. For the most part I have been really happy with the performance and mostly with the fuel mileage. Over my other set-ups I have run before, this one is by far the best on mileage. I have gained 4-5 miles per gallon over the stock single Mono-jet.

What I didn't like was the lag from cruise to part throttle, such as passing or long up hill runs. The engine felt weak and made a lot of noise for little power. Full throttle was all right, but weak. I lived with it since the mileage was so much better. What I didn't know was weather it was rich or lean.

About a month and half ago I ordered a stand-a-lone Wide band air fuel gauge. I had to install an oxygen sensor in to the head pipe, but the rest of the gauge was a simple install with only a couple of wires to connect.
It didn't take long to see where the problems were with metering. At part throttle it was going lean and full throttle was on the high side of the what is considered the power ratio.

At 65 mph, fairly level ground, I was seeing 14.5 to 14.9 A/F, part throttle was 16.7 and higher, full throttle was in the 13.5 range. I had a makeshift throttle positioning gauge just to see what was happening. Throttle positioning gauge was a simple card board gauge with a spring pull pointer tied to the foot pedal by a long string. I marked idle and full throttle, then divided in half for 50% opening. All my driving around town was at 20% to 25% throttle. Highway was 18% to 20% throttle.

Vacuum readings were at 9 to 10 @ 65 mph, 20 @ idle, 18 @ idle in gear. I was happy with that.

I poured over all the W-1 papers I had looking for metering rods. I found what I was looking for in the Carter #420 W-1, 1939 Chevrolet , I am running dual #574's, the 1946 models. I had been running metering rod #75-485 which has three steps, .067" - .062" - .046". The new rod is #75-342, also three steps, .069" - .059" - .043. So its two steps leaner, three steps richer at mid point, and three richer at full throttle.

This single change made a huge difference in over all performance. Throttle is crisp, idles better, mid range is great, and full power is where it should be. From a dead stop to full throttle, the bog is gone, and power comes on steady and strong. A/F ratio's changed greatly, cruise is now in the 16.2 to 16.8 A/F ratio ( ideal fuel mileage range ), mid throttle dropped back to 13.5 to 14.2, and full throttle dropped to 12.7 to 13.0. I have read a lot lately on A/F ratio's, there are two schools out there, racing ratio's and mileage ratio's. I am leaning towards the mileage side since a stock 250 is not a race engine.

For me, the expense of the gauge has all ready paid off. With one metering rod change, I am really close on ideal tuning. I went back and adjusted the rod hight using a dial indicator just to see how the engine reacted. With a .040" hight change, I changed the ratio's one full point on the wide band. I raised them to move the mid throttle power curve in sooner.

I need some more drive time and a long trip to dial it in further, but for now I am really happy with it. Since it's running better, the awful smells of fuel are gone after shut down, so I can park in the garage without letting it cool off out side. Wife is happy about that!

Here is a link to the gauge I am using, I picked a color close to the '37s gauges. With more money involved, they would add a face to match just about any gauge you can think of.

http://www.speedhut.com/gauge/GL258-AFWB-09/7/Standalone-Air-Fuel-Wideband-O2-gauge-8-5-18

Joe

I've made dozens of road tests with an OTC 4-gas exhaust analyzer running off a 115 volt inverter, and you're right about getting some amazing results. There's nothing that beats actual numbers on the road that not even dyno testing can provide.

The theoretically ideal air/fuel ratio (called "stoichiometric") is 14.7 parts air to 1 part fuel. That's what all closed-loop computer systems are looking for to give the catalytic converter the best shot at controlling exhaust emissions. Best power happens at about 12.5-13:1, and best fuel economy at light throttle comes in at around 15.5:1 or so. It looks like you're pretty close to ideal with the current setup. Adding CO and CO2 readings to the oxygen percentage and air:fuel ratio helps to fine-tune the diagnosis, but that takes a $2500.00 machine the size of a small toolbox!
Jerry

Great post Joe!!!!!

I have always liked the Carters because of their metering rod technology, and you are proving why!

While the extra effort in tuning can be intimidating to some; use of the proper tools, and testing can be so rewarding in all phases of performance.

I have "pushed" the W-1's for years in multi-carb setups because the metering rod is physically connected to the throttle.

The later YF's can be a bit better because the vacuum level of the steps can also be tuned by changing vacuum piston springs (if one has them), but this just adds another variable (challange) in the tuning process.

Jon.

"I have "pushed" the W-1's for years in multi-carb setups because the metering rod is physically connected to the throttle."

Jon,

Is there a source for good W-1 metering rods and main jets except by buying NOS carb kits or used carbs to get them?

Like Joe I have a 420S with '37 Chevy jetting on my '36 PU engine. It runs great with that jetting but it's always tempting to get it running even better. I've owned this PU since 1965 but no project is ever complete.

Ray - the 420s is the factory suggested carb to replace the original on the 1937 216. Calibration should be about as good as it gets.

If you really want rods, they come up on ebay fairly regularly; and I am told the grumpy old hillbilly in Missouri can custom cut them to any specification.

A bit of trivia: we sold a set of 574s W-1's to a gentleman that was tired of the Johnsons on an early V-12 Cadillac. He stated the car had never run nearly so well on the originals

Jon

Jon,
Thanks for your input. Do you only sell full carbs? I had emailed you about the brass ball underneath the plunger on the Carter YF2100s and no help - I had to buy another YF2100s and the other one is sitting..Any takers?

Jon.

Thanks for that pointer on the application of the 420S. With 1939-40 jetting it didn't work well on my '36. Trying various main jet and metering rod combinations, keeping detailed notes on the effective jet open areas at the rods' large and small diameters and keeping detailed notes on performance brought me to a 94 main jet and a 1-step lean 1937 Chevy metering rod. With that combination the 207 cid engine ran well but had a very slight surge at barely cracked throttle openings. Going slightly richer to a standard 1937 Chevy metering rod yielded a "just right" seat of the pants feel accelerating, cruising at a steady speed and climbing some of the steep hills around here. I wonder what Joe's air-fuel ratio instrument would show?

If you really want rods, they come up on ebay fairly regularly;

Yeah, a guy with the handel "Ice racer" has them but he's selling those carburetor parts in fairly large lots, not individually. I'm a geologist, not a professional carburetor rebuilder like you. What would I do with 10 or 20 of the same jet, metering rod or check valve?

and I am told the grumpy old hillbilly in Missouri can custom cut them to any specification.

Missouri? Would that be you?

I got lucky when I needed metering rods, "ice racer" had the ones I was after in a set of three for a decent price.

What surprised me the most, is how much of a change in A/F ratio a little change in metering makes. At idle, a 1/4 turn of both mixture screws will change the ratio 3 to 5 point. I am getting good at very slight adjustments.

Joe,

Do you have the pointed rod that is used to measure the distance between the main jet and the metering rod bell crank? It is used to adjust the length of the linkage between the throttle arm and bell crank. If not, I can send you the measurements of its length and point angle.

Ray - please see new topic - Carter metering rod technology

Jon

No, I do not have the rod, but since I can tune using the wide band, I can get really good results without the setting tool.