Tuning your Stromberg 6×2 for the street
It’s not hard to see why every hot rodder loves a Stromberg 6×2 system. It’s an eyeful from every angle. And it hauls ass too. But don’t forget that 6×2 systems were generally designed for racing, so making them work effectively on the street is another question altogether.
Now, we’re not going to be talking about which Stromberg 6×2 kit to select for your intake here. We cover that in another tech article. We’re talking about setting up your 6×2 to work better…
No leaky carbs.
First off, we better remind everyone that a 6×2 system is no place for worn out old 97s. You need good reliable carburetors with good fuel metering, no play in the shafts and no air or fuel leaks. One air leakers is a problem for good idle. Six fuel leakers is a problem for your personal safety.
Racing. If you’re genuinely using six 97s to go racing then buy a Stromberg 6×2 direct linkage. And set the pedal link to open all six at the same time – quickly.
On the street. We can’t give you a definitive answer for every application. But we can say that, whatever you do, you’re probably going to look at a linkage based around two Stromberg TwoStep 3×2 progressive linkages, plus a Back-bar kit to join the two banks of carburetors together. We cover that in another tech article.
So let’s look at some basic principles, remembering that one setting does not fit all applications, and the weight of the car, gearing and rearend ratios, engine tune and drivability, your favored freeway cruising speed, and more, can all play a part.
Pedal response. As a rule, you want smooth throttle operation with a slow pedal ratio. A throttle like an on/off switch is no fun on the street. Now, your pedal ratio and travel are probably fixed, so being able to change things at the linkage end is important.
There are three adjustment holes at the top of the long back bar levers. And if you link your pedal to the highest hole and set the link to the carbs in the lowest hole, you will get the slower throttle response. Remember, of course, that you must never hit Wide Open Throttle (WOT) with any travel left under the pedal, as forcing it further could damage the linkage, stress all the links and, worse, break it and leave your motor uncontrolled. Believe us, we have had snapped linkage arms returned for warranty!
Six carbs working. Ok, so you want the full 6×2 street experience? Let’s talk about linkage adjustment. With the progressive sliding links on the top adjustment holes in the center carburetor levers, and the sliding stops adjusted so that all three carbs on each bank reach Wide Open Throttle (WOT) at the same time, the system will run on the center two carburetors from idle, bringing the outer carburetors in from around half throttle. On a 3×2 you have a lot of versatility on bringing the outer carbs in earlier or later, but on a 6×2, it’s not that easy because the slider rod MUST be attached to the top hole in the long center lever because the bottom hole is taken by the link to the back-bar. And if you swap them, those back-bar links hit the back carb fuel inlet.
Even then, we’re not completely out of the woods. On a 6×2 progressive linkage, the sliding rods on each bank must join to the front carburetors because of clearance issues with the back-bar. Why is that a problem? Because the sliding rod rod then causes issues with your fuel supply. Rather than covering this again, check out our tech article ‘Chosing the right fuel lines for your 6×2’. There’s a link below.
One more thing. You can still bring the outer carbs in later, simply by adjusting the rod stops on the sliding rods. You won’t get primaries and secondaries to all hit WOT at the same time, but on a light car with a big motor, that might not be such a bad thing. !
WARNING! Do not use the linkage in any configuration that will cause sticking and binding, which could result in uncontrolled engine speed, property damage, serious personal injury or death.
BIG97 Primaries. We are seeing a lot more folks using two BIG97 Primary carbs in the center of their 6×2 because with 500cfm in the primary location, a lightweight street driven hot rod will pretty much run on only those two carbs, making life easier around town and on the freeway. Might even save you a few bucks on gas too. Just back the progressive linkage off so the outers rarely come in.
Return springs. Make sure all six carburetors snap shut when you lift off at the pedal. We mean it! All Stromberg linkage kits are supplied with our Snapback return springs. They work great and you can get more from your Stromberg dealer (ask for 9154K). Remember you already have the accelerator pump springs helping return the throttle so you shouldn’t need a crazy number of springs. So don’t use springs as fix for poor linkage alignment. If there is any slowness in the throttle return it is probably at the pedal end or because your swivels are misaligned. Eye the system from above and adjust the levers along the throttle shaft or Back-bar as required.
Jetting. We cover jetting in other How-to’s and the message is the same for a 6×2 system as any other. With engine tune, elevation, local gas laws, ethanol content and more, each application is different, so it’s almost impossible for us to guess what you need. So we usually say start with the standard 0.045 mains and see how it works from there. Though as a rule you’ll probably end up with smaller jets and power valves.
In tuning, you might want to try disconnecting some of the accelerator pump lever links (like all outer four at first) to test reducing that top end enrichment and also the amount of at raw gas injected when you pump the throttle. Remember, most 6×2 intakes were designed for racing at full throttle. If you crawl around town and rev it at the lights, you will get hot, raw gasoline in the bottom of the intake. I’ll repeat that. Hot, raw gasoline…
As always, getting the car/engine onto a dyno of some sort will help you measure what is happening and make informed decisions about tuning. One small tip: Once the linkage is set-up, it is often easier to leave it in place and remove the carburetor bowls off the bases to change jets. Keep persevering and you will find a good level of tune that suits your engine and your driving style.
Your link to the pedal. Stromberg recommends a mechanical pedal link for all multi- carb systems. Ideally, your 6×2 Back-bar can be connected to the pedal via one of the long levers that work the two banks of carburetors. But if these don’t line up with your pedal link, you can add a third long lever to the Back-bar shaft with Stromberg kit 9096K (Long linkage arm/swivel) positioned to align with your throttle pedal ‘pull’ point.
As with all our Tech articles, we welcome customer feedback and other input. Email us (firstname.lastname@example.org) with your thoughts and if it adds to the debate, we’ll add it in. Thanks for listening.