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Carburetion and induction

20 apr 2022

This section covers induction, fuel and air intake: carburetion and EFI. There's a lot of work covered in these pages, most of it foolish. The more exotic research is below, but the two solutions that have worked out best overall, the Carter YF/YFA and two small Weber two-barrels, are covered first. I have also used two larger performance-only Webers, the 40 IDF and 44 IDF, and a Sniper Autolite 1100 EFI system and have notes on each below.

AMC had two general carburetor options for the (pre-1964) American: a single-venturi model (Holley 1931, 1904, 1906 or 1908), or a two-venturi Carter WCD. In Classics, Carter AS or RBS was used, depending on year and transmission. The WCD requires the matching two-hole intake trough cover plate. These setups are somewhat scarce, but available. The WCD provides somewhat more high speed performance.

Carburetor choices

Any of those OEM choices would be fine, if suitable examples could be found and if replacement parts compatible with modern fuels were available. Sadly neither is true today in 2022. The aluminum castings themselves wear (pitting in the venturis, and throttle shaft wear) and worse, lack of replacement parts, and often replacement parts that do not withstand modern fuels.

In my opinion the small Holleys are of poor design, and I will never run one again (easy to say because parts aren't available anyway). The float bowl design has fuel wet on the gaskets; they leak fuel onto the hot engine eventually. The new fuels are both more volatile and more corrosive and old gaskets not fuel proof.

The practical choices for carburetors on this engine are the Carter YF/YFA, The Carter WCD for two-barrel versions of the engine, and the Weber 32/36 DGEV, the most tunable and best performing of the lot.

Carter YF/YFA

Today (2022) for various reasons the Carter YF or YFA is available; used, new-old-stock, and new manufacture, mostly chinese-made. The imported new carbs vary in quality, but good ones from reputable importers seem just fine, there are lots of advantages to new metal, and man, are they cheap.

The YF and YFA (YFA is shorter (hood clearance) and has minor design improvements over the YF, but are interchangable for our purposes) were used on AMC sixes, but not the 195.6. It does bolt right on, but the throttle linkage is usually incompatible and requires fabrication. Most YF/YFA models will need re-jetting and slightly different adjustments. The YF may have hood clearance issues when used in the lower-beltline cars, 1964 and up.

But the Carter YF/YFA is a very good carburetor choice, maybe the overall "best" considering availablity and tuneability and reliability. They are well made and of excellent design. Parts are available, new, including fuel-proof rubber parts. There is much knowlege of them about. It has no dangerous design flaws (fire!).

20 April 2022 Specifics on installation and tuning of the Carter YF/YFA has been moved to the Carter YF/YFA page.

Carburetor parts sources

There are many, but these are my favorites, for quality of parts and quality of business services.

Mike's Carburetors, carbs, parts, rebuild kits, documentation.

Quadrajet Parts, a broad range of parts including alcohol-proof accel pumps.

Top End Performance, I buy Weber carbs and parts from these folk, they're great. Webers are made in Spain. I'll buy cloned YFs but I will only buy genuine Webers -- here it matters, as they are tweaked by hand, jets are individually flow-benched, and the precision requires good quality control.

Holley Sniper Autolite 1100

The Weber 32/36 DGEV

In my opinion this is an ideal carburetor for this engine and the easiest to install and get running -- but it requires rejetting and tuning to be usable. The tiny primary venturi means that this high-torque, long-stroke motor has an accurately metered and tunable mix at speeds below 2000 rpm. The larger secondary is progressively coupled, begins opening at half-throttle. At wide-open-throttle the two venturis are larger than the Carter YF. I found it to be well behaved under all circumstances and easy to tune.

Because the two venturis are different sizes the carb mounts to the trough rotated 90 degrees. Looks funny, works great. There are two adapters available for this carb; both bolt to a "Carter YF" type flange. The one I got from Top End Performance, and the Trans-Dapt version (nearly indentical) need work with a file to fit. The carb-end holes are off and need to be filed/notched to accept the bolts. The large oval hole accommodates the bores fine. Make sure that the gasket seals correctly. I had to remove the manifold studs and use 3/4" bolts to mount it due to tight clearances.

There will be a fair amount of work required to couple the throttle linkage. This is not a bolt-in project. The carb on it's adapter puts the throttle higher than the twist rod. I extended the rod pivot at the firewall and welded up an adapter for the carb end. You could convert to a modern cable throttle, but if you have an automatic with transmission cable you will have to retain that which is tricky.

Redline makes a "Jeep Weber kit" that bolts onto the 195.6 OHV's most common single-barrel trough cover. The adapter raises the carb enough to clear the valve cover (which can be removed with the carb installed).

The 32/36 DGEV will fit under the hood, with air cleaner attached, on the pre-1964 Rambler Americans. I am told it hits the hood on 1964-up Americans.

Here's the kit from Top End Performance that I used. Link valid as of April 2022; it's Kit 550. There's a hilarious note in red that says "this carb is too small buy larger" which is certainly aimed at the sports car crowd. It is the correct carb for our 50, 60 year old, slow-turning engine.

Pressed-in fuel inlets have been known to pop out and pour gasoline all over the hot engine; remove, tap 1/8" NPT, install brass nipple.

Out of the box this carburetor will run terribly. The float level is not set correctly and the jets are chosen for some hypothetical small four-cylinder with big bores and short stroke. The procedure to tune them is very straightforward, but utterly alien to people used to American type carbs. Follow the procedure exactly and you'll get great results.

Here are my Weber tuning procedures.

Here are my settings, use these as a starting point.

low speed jet 55
idle stop screw 1/2 turn
idle mix screw 1.5 turns out
main jet 140
air bleed 170
float level 35mm

Weber 38/38 DGV

The 38/38 is almost identical to the 32/36, but the two venturis are the same size, the carb is not progressive (both open at once). Though intended to be used as one venturi feeding one half of an engine, on the 195.6 and the adapter it will be plumbed as a "one barrel" carb and both V's will feed all cylinders at once. This and the lack of progression make it less attractive for stock engines. If you are absolutely certin you will be keeping RPM up and throttle open in a range that the engine will flow the CFMs, it's a fine choice. It's the carb currently on my roadster. The 38/38 DGV is bolt-compatible with the 32/36 DGEV.

Pressed-in fuel inlets have been known to pop out and pour gasoline all over the hot engine; remove, tap 1/8" NPT, install brass nipple.

Here is a copy of my 38/38 tuning notes if you care. Please refer to my notes on Weber carburetor tuning for details on these carburetors.

Weber IDF series

Less practical Weber carburetor choices are the 40 IDF and the 44 IDF. I have used these on my highly modified roadster engine, which currently has the 38/38 DGV installed. The 40 IDF is great at WOT above 3000 rpm; you will find it undrivable on a stock engine. The 44 IDF was far too large to be tuneable on even my roadster; thr 40 IDF replaced it.

Please refer to my notes on Weber carburetor tuning for details on these carburetors.