The Carburetor Shop LLC
204 East 15th Street
Eldon, Missouri 65026
Selection and synchonization of triple carbs on a six cylinder inline engine
Since we receive more inquiries concerning 235 Chevrolets, we are using this engine as our example; but the selection process and the synchonization process are independent of make.
For best results, the very best thing is to do one’s homework BEFORE one purchases anything. A triple setup MAY have clearance issues. There are several major criteria in the selection of one’s puchase, but the first criteria is how the unit will be used. Consider that 50~60 years ago, triple carb manifolds were sold for RACING! Today, while a very small percentage will submit their vehicles to the race track, most are interested in triple carbs for either LOOKS ONLY, or looks with a modest increase in performance. These two uses have vastly different requirements in carburetors.
Typically, the manifold sold in the period would be drilled for three carbs the same size as the original (a 216 Chevrolet would have 3 S. A. E. size 2 carbs, whereas a 235 Chevrolet would be drilled for 3 S.A.E. size 3 carbs). By using this arrangement, the user could order two addition original carburetors from the dealer to go with original carb on the engine. At the same time, the user would install a full-race cam, a magneto ignition, headers, high-compression pistons; all to go with a numerical higher rear-end ratio BECAUSE THE ENGINE WOULD HAVE AT BEST A VERY HIGH IDLE, AND VERY LITTLE LOW END TORQUE. This is a good selection for a trailered race car, but a poor selection for the “cruiser” on the street.
The second criteria is to decide if solid linkage, or progressive linkage will be used. We highly recommend solid linkage unless this is strictly a “show” item, and the outer 2 carburetors will be “dummys” (in place for “looks”, but not used). The reasoning for this recommendation is really quite simple. If one uses progressive linkage, then the center or primary carburetor must be of sufficient size to idle well, and run the engine well at normal cruise RPM. Since the manifold is designed for three carburetors, the runners to the outer cylinders will not deliver the same A/F ratio as to the center. To prevent a lean A/F ratio on the outer cylinders, the primary carb will have to be artificially rich, thus reducing fuel mileage. For performance work, it is very difficult to get the end carbs to come in without a lag of a third to half a second. If the reduced fuel economy and the lag are acceptable to the enthusiast, then progressive linkage may be used. Carburetor selection for progressive linkage is easy. Simply use 3 of the original carbs for the engine. I am not saying that progressive linkage won’t work, as many use it. But it cannot work as well as solid linkage. Did you ever see an XK-E or Healey 3000 with progressive linkage? Or the triple YH setup used on the early ‘Vettes?
Since the manifolds of today are basically copies of the manifolds of yesteryear, generally the street enthusiast will need to modify the manifold for smaller carburetors. Example: for a stock or modestly built Chevrolet 235, an enthusiast might choose 3 original Carter W-1 carburetors as used on the Chevrolet 216. These will be marginally on the large size, but can be dialed in without too much effort. A better choice (but possibly more difficult to find) would be the Carter WA-1 carburetors used on the small (202 CID) Husdon in the early 1950s. Two were used on the Hudson; three work well on the 235 Chevrolet. The key in selection is to choose carburetors that are individually too small for the engine. The manifold would be drilled for size 3 carbs (2 15/16 inch mounting pattern), but the 216 carbs and the Hudson carbs are size 2 (2 11/16 inch mounting pattern). There are three methods of doing the conversion: (A) use size 3 to size 2 adapters (extra cost, and looks “hokey”); (B) slot the holes in the carburetor (no additional cost, but looks even more hokey); or (C) have a good welder fill the original holes in the manifold, and then drill and tap for the correct size (extra cost, but looks much more like a factory installation, and weren’t looks the major criteria?).
If you plan to use on a trailered racecar, use the larger size.
The third criteria for selecting carburetors is that the EASIEST AND LEAST EXPENSIVE good results will be obtained by selecting either (A) carburetors which were originally designed for used in a multicarb environment (example: Carter WA-1’s used on the Twin-H Hudson) or (B) carburetors with a mechanical (as opposed to vacuum) power system. Carburetors with a vacuum power system may be used, but the tuning MAY be more difficult. If you have a spring winding kit and feel comfortable hand winding small precision springs, you may ignore this paragraph. The Carter W-1 units have a mechanical power system, and the Hudson WA-1’s were designed to run in a multiple carb environment.
The next criteria is the one that gets the most arguments – the brand of carburetor to use. After almost 50 years of working on carburetors, we recommend Carters for most applications (readily available, reasonably priced, and parts readily available). For the high end user to whom cost is not an object, but perfection is the goal, we suggest either Strombergs are Zeniths. Other brands may be used, but there are no others that we recommend. In any event, one should choose a brand with which the user or the mechanic of the user is extremely familiar. In any event, ALWAYS use matched carburetors by tag numbers. Trying to use non-matched carburetors is simply asking for trouble.
If you start with used cores, acquire good rebuilding kits (we would suggest the ones we make); and rebuild the carburetors to absolutely stock calibration. By building to the stock calibration, you build a repeatable “baseline”. Calibration adjustments, if necessary, may be made later.
Once the carbs are rebuilt (or new carbs), one is ready for the installation and synchonization procedure, which is independant of brand, type, and size. Solid linkage will be required (unless you have some funky home-made manifold that has both carbs feeding into a centrally located plenum). Progressive linkage is not an option.
Synchonization (solid linkage)