Speedway Motors Stromberg 97 - Tri-Power In Under An Hour - Tech

...as are the 0.045-inch main jets.

Here's a neat cutaway from a display carb showing the details of the main jet location on the bottom of the float bowl.

Changing jets is still tricky with the carburetor installed on the intake manifold, especially in a multiple carb setup.

With the Edelbrock intake bolted to the engine and torque'd to spec, we installed each carb with the mixture screws (the two small guys on the front of each base) a turn and a half out. This is a pretty good baseline setting that we'll dial in later. Each carb was then plumbed to the Edelbrock 3x2 fuel block. Note the absence of any linkage, save for what existed coming from the pedal.

The first step is to get the engine to fire and idle at a decent rpm. After ensuring that the two-end or secondary carb idle speed screws were backed out sufficiently, we turned in the idle speed screw on the primary carb to help bring the engine to idle. Once fired, the idle speed screw is further finessed until the engine hovers around 800 rpm.

The next step is to sync the carbs. This ensures that all three are pulling the same amount of vacuum at idle. A UniSyn Carb Sync Tool is placed over the throat of the primary carb and is adjusted until the ball floats in the center of the gauge.

Next, the secondary carbs are checked using the syncing tool. Both carbs required adjustment on the idle screw, which bumped the idle rpm of the idle speed screw engine up slightly. By going back and forth between the primary carb and secondary units...

...small adjustments were made until all three carbs measured the same vacuum via the UniSyn gauge (synced) and the engine idled at a proper rpm rating. At this time, the primary linkage between the throttle pedal and primary carb can be attached.

Here's the "secondary" or progressive portion of the Eelco linkage kit. This mates the two secondary carbs together and regulates when they open.

The two lock rings on the upper shaft flanking the spring do two things. The left one retains pressure on the spring, which in turn keeps either secondary carb from opening up under vacuum. The right ring determines when the secondary carbs open. The stud attachment point connects to the primary carb linkage and slides along the linkage shaft, maintaining the spring pressure to keep the carbs closed until it contacts the right ring, which allows the linkage to open up the secondary carbs.

With all three carbs sync'd, the secondary linkage can now be installed on the throttle shafts of the secondary carbs. Care must be taken to ensure that the linkage is attached without moving the throttle shafts off their "idle" settings, thereby changing the tuning that was just set.

It takes a bit of trial and error to set when the secondary carbs kick in, we adjusted ours to come on just before the primary carb reaches half throttle. A bit of driving will tell us if that's where we like it. The easiest way to determine this is to set it to when a 4-bbl carb's secondaries would come on but it really just comes down to personal preference.

With the linkage installed, the last thing to do is to tighten down all the jam nuts to ensure that it doesn't come out of adjustment.

It's a bit cluttered due to the placement of the fuel block on the driver side of the intake with the linkage behind but it allowed for the easiest routing of the fuel line from the stock mechanical fuel pump.

With the fuel lines removed, you can get a better idea of what the installed linkage setup looks like. Note that all three carb arms are clocked at the same 10 o'clock setting. It's very important that they're parallel and cannot be opened over center, causing a potential stuck wide-open throttle situation. We bent a piece of tubing to clear the linkage and fuel lines that attach the throttle pedal linkage to the primary carb arm with a pair of Heim ends.

The passenger side, however, is much cleaner, with only the choke linkage, idle screw assembly, and accelerator pump linkage visible on the three carbs. We topped off the trio of carbs with Tru-Helmet air cleaners to give the setup a classic hot rod vibe.

The engine compartment is looking pretty good and, save for a few items, this shot could have been taken in the late-'50s. A bit more tidying up is in order before our driver becomes show worthy, but we're getting there.

Two Quick Stromberg Tips: Taken from a Ford Service Bulletin from 1936, this diagram compares the two new more common Stromberg carburetors being introduced at the time, known in hot rodding circles as the 97 (A) and 48 (B). The 97 gets its name from its venturi diameter (0.097 inch) whereas the 48, with a venturi diameter of 1.03-inches gets its name from its main jet size, 0.48 inch. Another nominal difference was the means of shortening the stroke of the accelerating pump for warm weather on the 97. This setting shortens the stroke by 3/16 inch.