Carter AFB 3665S question.

I was wondering if there was some one with some experience with a carter 3665S carb (’64 riviera, 425 CID) and changing the jets and metering rods.

Since I’m planning a major overhaul of the carb I also want to replace the jets and metering rods, but I can’t find any metering rods in the original size (0.0695x 0.063).

No problem finding jets in the original size (Primary -.092,Secundary -.089) but the rods that come closest are 0.068 x 0.057.

No idea whatsoever how this is going to turn out.

Anyone with some thoughts / experience? Other size jets to compensate for the different size rods :confused:.

This article from Mike's Carburetor Parts explains how the Carter metering systems works. Second I think Daytona Parts can make Carter metering rods. See link.

http://www.carburetor-parts.com/AFB-Metering-Rods-Jets_ep_298.html

http://www.daytonaparts.com/

I already read the artice from Mike's Carburator Parts and it looks to me that it comes down to trial and error.

So, before I go that way, and end up with several jets and metering rods lying around, I was hoping that someone already went down that road and could point me in the right direction i.e. the right diameter sizes, jet / rod-combination.

To quote a good friend (Tom V.) from another forum: "Engineers do things for a reason".

UNLESS you have made MAJOR modifications to the engine (a slight overbore to clean up the cylinders is not a major modification), building the carb to stock calibrations is an excellent starting point.

Metering rods in any size are available by mail order, but as most configurations must be custom made, they are not inexpensive.

Standard jetting was used up to an altitude of 4000 feet. Above that altitude leaner rods are recommended.

The use of ethanol-laced fuel MIGHT (or might not) require a slightly richer rod.

The use of ethanol-laced fuel often requires a slight modification to the idle circuit.

Jon.

Marcel - you might find my new thread on Carter AFB tips helpful.

Jon.

Hi Jon.

Giving you a call was on my to do list for next week.

Could you put a number on "not inexpensive"?

Marcel - the price depends on the time spent. Generally 2 ~ 2 1/2 hours for two step rods (pair) up to maybe 4 hours (pair) for 4 step rods with a couple of tapers.

Figure machine shop time per hour in your area. You probably will not be far wrong.

Jon.

Hi Jon.

I don't know what an hour shop time in the US is, even worse, have to figure out what it shop time in the Netherlands is for this kind of work.

I took the rods out and tried to measure them, as good as I was able to. Original would be 0.0695 * 0.063, I measure 0.0685 * 0.0622.

No idea of this difference is of any meaning. It's only about 1.2 %. Maybe it's within the margin.

I'll take the rod to work tomorrow and try to measure it again, so I'm sure about the size.

Marcel.

With both measurements off by almost exactly the same amount; I would suspect the micrometer, and do as you are doing ......try a known micrometer. My guess would be that you are going to find your rods are standard.

While metering jets DO wear, especially the primary jets; rods seldom wear. Generally rods are replaced for one of four reasons:

(1) Major mechanical modifications to the engine

(2) Moving to a much different altitude

(3) Replacing a broken rod because some previous "expert" tried to install the airhorn with the rods in place.

(4) Replacing a rod with high wear where it contacts the piston or rubs through the housing. This can occur on really high (maybe 250,000 mile) mileage engines.

You might also check for the part number stamped on each rod. It should be 16-167. To read this number, a clean rod, a good magnifying glass, and a pair of "young eyes" are quite useful. Look about midway in the length of the rod.

Jon.

Had the rod measured today and it turned out that there was nothing wrong with the micrometer I used. Even found out that the rod was kind of oval instead of round.

This evening I took the other one out and it measured exactly the same.

With an extra good magnifying glass (to make up for my ”not so young” pair of eyes) I could read the part nr. and it was 16-167.

I decided to put the rods back, enjoy the car for as long as summer will last, and take the carb really apart in winter, have it cleaned ultrasonic, and inventorise then what I exactly need. Not sure what I’m gonna do with the rods, but I have some time to think it over.

Thanks for your help.

Marcel, from my experiences, metering rods MIGHT have some wear on them, but that's erring on "the good side of things", for many, yielding a marginally-richer mixture as a result, throughout the total calibration range.

I purchased a Carter Strip Kit for the AFB carbs, years ago, when they were available (i.e., 1976 or so). I played with metering rods, going richer and a little leaner, but my mpg logs showed no significant difference in mpg and no real "seat of the pants" difference in performance. Later, I purchased a similar kit for a ThermoQuad on another vehicle. I still have them both . . . with the little paper spec manual that came with them.

I'm curious why you might consider changing jets/rods as a part of a carb rebuild? Just curious.

In "metering rod carbs", if the total mixture is a little rich or lean from optimum across the full fuel calibration map, then you change the jet. If it's only off in one operating parameter (i.e., low speed, cruise, power), then you change the rod. If the power mixture is a little late coming in, or comes in too soon, then you change the spring under the "power piston" (which holds the metering rod). Additionally, if the jetting requirements of the vehicle have been met, but the (possibly "bigger" replacement cam) has enough duration to result in lower manifold vacuum at idle, a different metering rod spring might be needed to ensure that power enrichment might not happen too soon.

NOW, if you want to do all of this "seat of the pants, vacuum gauge, and stop watch", then you can download the Edelbrock AFB Tuning Manual from the Edelbrock Carb website. It's about 50 pages, as I recall.

The Edelbrock AFB is very similar to what Carter built, in design and function. You CAN purchase a calibration kit from them (rods, jets, springs) and probably get the tuning manual as a part of that deal. I think their website will also detail the contents of the kit (metering rods and specs, plus jet sizes).

IF there was one area I'd be concerned with, it might be the power piston springs themselves. If the springs might get weak with age and use, that might make a part-throttle enrichment situation happen a little later than usual (or original), resulting in a leaner mixture. But then again, this might not be a completely bad thing either!

You might also be more concerned with throttle shaft wear between the shaft and the carb's body. It could also be that the additional richness of the slightly-worn jets/rods is compensated for by the additional "vacuum leak" from wear of the carb body/shaft interface? I know there's a kit to address this issue on other carbs, but I'm not sure about AFBs. Carbking would know more about this, I suspect.

ALSO, don't forget to get the CORRECT carb base gasket set for that vehicle--period! It can be unique to Buicks and other GM products, but make sure it's of, at least, OEM quality. For some, having a leather accel pump is better than the rubber pump cups.

The other thing is, by observation, unless there was some significant operational issue with the carb, don't expect a big change in how the vehicle runs after the rebuild.

Altering the OEM-spec metering specs to better accommodate ethanol'd gasolines CAN be a little beneficial AND something which can be reversed later on, if need be.

Just some thoughts,

NTX5467

The reason for this is as follows; I bought the car about a year and a half ago, and when I bought it, it ran terrible. First thing I did was taking the carb apart, clean it (there was a lot of carbon inside), new gaskets, new needle and seats and almost everything else that was in the rebuilt kit. Checked also for wear between the shafts and body, but that was really minimal.

I changed a lot the way the engine ran, but it still ran kind of rough. So the other stuff I replaced over the last year are;

new spark plugs

new spark plug wires

new rotor and distributor cap

changed the point for a pertronix

new distributor chain

new fuel pump

checked for vacuum leaks (several times, no leaks)

checked for air leakage in the intake area (several times also, also no leaks)

fiddled around with different weights and springs in the distributor

…..hmm, that kind of sums it up, at least, the stuff that is related to the running of the engine.

Still the engine runs kind of rough. I’m comparing it to the 350 in my ’68 Lesabre that runs much smoother. Problem is, that it isn’t easy to find another ’64 Riviera with a 425 to compare it with. At least not here in the Netherlands.

Anyway, this made me decide that I would take the carb apart, have it ultrasonic cleaned and change whatever there is to change so I can rule out that these things would still cause the rough idling / running of the engine. Since I have to order the stuff from the US, and have to pay the shipping to Europe anyway and parts like jets, springs, etc. don’t cost the world, I wanted to, like I said, replace whatever is available to replace.

In my search for those parts I stumbled across the metering rods, and since some site’s offer them for about $13 a set I thought to replace them too. But I couldn’t find the right size, which made me post this thread.

After your reply, and the replies from Carbking, I probably keep using the ones I have. Nevertheless, I learned a lot about metering rods, jets and carter carbs the past weeks.

One thing you haven't checked is the compression. Variation in compression between cylinders can cause rough running.

I was afraid I forgot to mention something, and that was that I also checked compression.

Compression turned out to be as follows;

1-185 2-175

3-170 4-170

5-170 6-180

7-170 8-180

Also placed a new vacuum advance unit (forgot to mention this also).

It’s not just the rough idling but there is also a slight hesitation when accelerating (acceleration pump is working, vac. advance is working), so this is something that maybe can be fixed by changing the spring underneath thepower piston.

Something I just have to try and see what the effect of changing the springs is.

contact Ted at http://oficlassiccars.com/

He rebuilt my carter on a 64 Riv and did a superb job. He really know his stuff.

Do you run ethanol gas in the Netherlands? I have a slight roughness at idle only with my Buick. Had the carb rebuilt by a reputable local shop, check compression, electrical. vacuum, etc. Everything spot on. I blame it on the gas available in our area and live with it.

contact Ted at http://oficlassiccars.com/

He rebuilt my carter on a 64 Riv and did a superb job. He really know his stuff.

Well, I'll first give it a thorough shot myself. Shipping it to the US and back to the Netherlands won't be cheap, so this will be one of my last options.

Do you run ethanol gas in the Netherlands? I have a slight roughness at idle only with my Buick. Had the carb rebuilt by a reputable local shop, check compression, electrical. vacuum, etc. Everything spot on. I blame it on the gas available in our area and live with it.

Yes, we do have about 5 percent of ethanol mixed with our regular fuel, on the other hand, the fuel in Europe has a higher RON number than the fuel in the US. We're having fuel with 95 (or even 98 RON). But the European RON number is measured differently than the US RON. To cut a long story short, European fuel with 95 RON would be US fuel with around 90 RON.

An acquaintance of mine has a 59 Pontiac that only idles nice with 98 RON fuel.

Haven't tried the 98 RON fuel yet, only the 95. But it is something I want to do as soon as I have to fuel up again. But at around $ 9.00 a gallon I try to be really economical.....with a 425 hahaha.