Getting my ducks in a row.... Working towards starting my 21-stud in the B4Cdan...I acquired an Offy Regular Dual intake and will be rebuilding two matching 94s next week with @scootermcrad . The one thing I don't have down pat is power valve selection. I've read several threads on the topic, but they all seem to be for the later 8BA/EAB engines that include vacuum advance distributors. Need to know what power valves to go with (thinking 3.5s in each, but some mention 4.5s) and what jets to use. Any help would be greatly appreciated!
I'm running two 94's on a 200 cubic inch four banger. I use straight non-progressive linkage which I assume you will be doing also. I am using 3.5's for power valves, and started with the stock 51 jets. I had a bog going off idle that could not be cured by fiddling with accelerator pump settings so I went up on the main jet size. I think that compensates for low velocity air flow you have when you add so much venturi to the intake tract with dual carbs. I had some number 54 jets so I put one in each carb and that cured it. It is definitely over carbed but it goes great and cruises at mid rpm's with no issues. The accelerator pumps are set on the middle setting and work fine. I clean plugs more often than I suppose you should because they do tend to get a little sooted up, but I'm willing to trade that for the kick in the pants with the dual carbs. If you wanted all the jets the same size I would try 52's. I am planning the same setup as you for a V8 and purchased 4.5 power valves, but that's for a motor that's bigger at 254 cubic inches. I think I would try 3.5's for the small 21-stud V8.
Better detail shots... Also, has anyone fabbed up their own straight 2x2 linkage (non-progressive) out of salvaged linkages? Pulled this one out of the small parts pile. Its EXACTLY one inch too long...which I'm sure I can fix, but trying to visualize how the rest would look....
Usually you tie the two carbs together on the other side - with an adjustable linkage that lets you tune the air-flow to match (side to side). Then on the passenger's side, you attack the throttle peddle to the rear location that you show. On the power valves, hopefully you purchased them from Daytona - or somebody that has the correct ones with the right sealing surfaces for the older 94 style carbs. If you buy modern Holley ones, they tend to leak around the gaskets. You really won't know which power valve to use until you run the engine - and put a vacuum gauge on it.
Thanks @Bored&Stroked I did not use extended shafts on these, but I don't see why I couldn't. I did find a pre-fabbed linkage from Charlie Price that does everything on the passenger side, but I'm open to options. I also purchased PVs from Charlie...3.5s...AND a power valve plug. Charlie recommends running only one PV as my small flathead really doesn't need double enrichment. I purchased two PVs, we'll see how it runs and proceed accordingly.
I connected mine using the old connectors like you show, be aware that the ends are spring loaded, one of them will be push or pull and will work against the spring to unclip itself. I cut mine in the middle and machined a union to join them with LH & RH threads and put a ball stud in the middle for the gas pedal linkage, mine is in a Model T and the gas pedal linkage is more to the right side than the left.
Dunno who the great minds would be, perhaps they'll come along and make themselves known, until then we'll just have to plod along the best we can.
I've been running two 94s on a stock 239 8BA using stock 51 jets and 6.5 PVs for 15 years with no issues. I would start with 51 jets and 6.5 PVs. (The engine vacuum levels really determine power valve selection) Synchronize and find out how it runs and drives. Make sure both carbs are built exactly the same! I would NOT block off one power valve, or run progressive linkage on a dual setup, two "recommendations" often given, IMO.
Check out Speedway Motors flathead catalog section for throttle linkage parts. They have some reasonably priced double linkage kits that you can probably adapt to your carbs. I used their PN 560-1006 double linkage for carbs spaced at 9", they have two others available for 7" and 3.5" spacing. They have ends that lock into place on the linkage balls so you don't have two worry about pulling against spring-loaded ends. They come with an adjustable ball to connect to your throttle pedal or bell-crank so they can be installed on the original throttle levers without needing to have extended throttle shafts and clamp-on levers on the "back-side" of the carbs. If you buy Model A throttle or spark advance rods for your linkage you can cut off one end and create a wide variety of linkage lengths to fit your application. The rods are 3/16" so they can be tapped for 10-32 jam nuts. I make adjustable links using 1/4-20 barrel nuts and cap screws with the heads cut off as shown in the photo below. I solder the threads and drill through the threaded area for the linkage rod, and through the opposite end for a cotter key. Maybe not elegant, but cheap and effective.
@dmar836 That's kinda what I was hoping to see when I started this thread. Not that these ideas don't hold merit (they're all well done), just looking for what would have been a war-time solution to dual carbs on a flathead. Guess I should have been a little more specific in my request. Keep 'em coming!!!!
A lot of aircraft parts came onto the hotrod scene during WWII. Carburetor linkage parts and other related stuff would come from small aircraft spherical rod ends - which we all take for granted today. You can buy all of this stuff from places like McMaster Carr. You really want as little friction/binding as possible in any carburetor linkage system. If you can, get both a right and left hand thread spherical rod end - with a 10/32 female thread in them. Then you can thread a piece of 3/16 rod with a right hand and left hand thread on each end - this makes it easy to adjust the spread without having to take the linkage off the carb. Here is a link to explore: https://www.mcmaster.com/products/spherical-rod-ends/shank-gender~female/
Received my goodie box with PVs and other goodies. Couldn't resist mocking them up... Still have to imagineer everything from my foot to the linkage ball, but I'll get there!
Not sure why the picts posted twice, but I used the Stromberg brand linkage off of extended shafts. I like the Stromberg linkage for they have a springs at each arm that is somewhat hidden. For the throttle, I just connected to the rear most carb. Works perfectly.
overfueling does a lot more damage than jut sooting plugs, it washes out piston rings and wears bearing through oil dilution.
@banjorear Nice work! Linking the carbs together on the driver's side and then actuating on the passenger side makes for a clean install. Unfortunately, I didn't use extended throttle shafts, so I must do everything on the passenger side!
Thank you. I appreciate it. Good news is you're early enough in the mock up to install them if you think it would help or make the installation easier.
Another note: When using extended shafts and those little die-cast arms, setup the arm angle so that straight up is at the center of the throttle travel (open to close). You'll usually find the arms will be at about 10 o'clock. Also, I've found that the arms we buy today are frequently not of the same quality as what I used to get decades ago - they will "slip" on the throttle shafts. What I now do is once I have the arms in the correct places, then I drill the arms and shafts and put a roll-pin in them. This guarantees that the arms stay where they are supposed too.
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