Don Terrill’s Speed-Talk

Just wondering about the feasibility of S&S Super E style Harley carbs with an inline engine of similar cylinder capacity. This would be three carbs on a siamese port six, basically a smaller version of a 250 Chev. The carbs are quite compact and seem to cope well with the vibration and uneven induction cycles of the HD vee twin and jets are available. They use a circular float with the mainjet in the center and the accel/decel forces would be in the same directions as on a bike. I think they should work OK with the old six but can't find any examples of prior usage.

Some years back, I considered fitting 3 Harley S&S carbs to my Chevy inline 6. Got in touch with Dan DaVinci and found out all I could about the Super G version of S&S carbs.

My interest then shifted to 42 HSR Mikunis. But put the project on hold whilst changing jobs and have only just now taken it up again since retiring. Have some Weber DCNF downdraught carbs here, so will use them.

Only sliding valve carbs I have really tinkered with were SU clones. Built an intake for a 2.4 litre Celica OHC engine in the early '80s. Mounted a pair of Datsun 240Z Hitachi carbs on the Celica engine and dropped it into a '68 Triumph GT6 chassis along with a 5-speed transmission and mounted a '72 Spitfire body on it with the GT6 front sheet metal up front. The car ran well and having no experience with sliding valve carbs up until that time, I managed to get them adjusted, sync'd and balanced. Following that, as long as you kept the oil reservoirs topped off, the carbs worked flawlesly.

Good luck with your project,

Harry

I wanted to do something similar with a flathead ford, I was going to use a b series . Essentially a b is a e without a accelerator pump. In stock form you have a idle,intermediate ,and a hi speed circuit. All coming in at wot. You can tune the timing on the hi speed with a adjustable air bleed, there is a spot to tune the air bleed on a b and d by the throttle shaft for the intermediate circuit if you fit it with a adjustable air bleed jet.
Look into a thunder jet, zippers performance makes them. Essentially another circuit added to replace the hi speed and make the main jet another intermediate circuit. 4 circuits instead of three.
I have used as many as three on one carburetor, with air bleed timing you can dial in a nice fuel curve.
The G series has a nice size bore but the venturi has a strong signal,part throttle has a surge of fuel that takes a little bit to drive through.
The most successful use of a g was a bored out Venturi to cut the signal to the main.
In the thunder jet paperwork is some good tuning tips,check out there website to see some of the d and b modifications they offer.
Nothing a creative mind and a mill can't do,just some good ideas

Consider the size of them. The E is 1.875" the G is 2.065 roughly. They are decent simple and tunable carburetors.

Those S&S carbs based on a Linkert. For a cool factor get a few of those. Their bodies are all Bronze w/ Zinc bowl. The Bronze polishes out beautifully. I had a panhead w/ polished Linkert & chromed bowl.

Johnno, is this one of the 9-port Holden red engines? If memory serves me well, I believe the 215 cu. in. Rover V-8s did quite well with two 1-3/4" SU's or Zenith-Strombergs? If your inline 6 is near to this displacement, an alternative might be to work up an intake that will accept 2 SU's and position them so as to provide equal fuel distribution to the 3 siamesed intake ports.

Just a thought,

Harry

Can the S&S carbs deal with a few PSI of fuel pressure ? They are easy to find at swap meets for reasonable prices and they look the part......Personally, I think Mikuni's are a better choice although the numerous jets and needles can be a bit confusing for tuning...Mikunis are also taller than the S&S if that matters...

I know you've asked specifically if anyone has tried S+S carbs on an inline, and I havn't, not on an inline, but I've tuned more than I can remember both on and off my dyno. They're an OK carb, but a bit crude and basic. The circuitry is fairly simplistic and the three circuits, idle/low, mid, main, don't overlap especially well and the more rpm range and powerband your trying to cover the harder it will be to get the S+S to work precisely. On a Pan or shovel, or even Evo's they can work fairly well given these engines are not especially sophisticated and are relatively slow turning torquers that spend the majority of their hours dronning along within a fairly narrow rpm range. And thats' not a knock...that is what these engines are built to do and they do it better than most. The S+S carbs will also work pretty well for drag racing. In that situation the carb will be working off only the main (actually the combined fuel flow of all three circuits) and will be tuned by main jet changing only, pretty much. If either of these scenarios fit what you're doing with your engine or describes the engine type you've got. The S+S carbs would likely work out alright. Just don't expect a perfect fuel curve. And before any of you start sending comments about how wrong I am about the "tunability" of the S+S carbs and how you and most of your buddies have no trouble at all making them work just as sweet and responsive as Fuel Injection, and I must just not know how to tune them, well a quick look at all the devices like the Thunder jet and similar circuit enhancers available for them I think speaks for itself. Again, I'm not knocking S+S carbs. I've installed a ton of them and wouldn't have any qualms about bolting one up to a Harley. But they wouldn't be, and aren't what I use on my own stuff, neither for street or racing. For sure, the Mikuni, or Keihin are superior mixers and are backed by endless amounts of tuning parts. There's a reason you see these on so many engines, both street and racing. My problem with both of these brands is that the way the mid range tuning parts, especially the metering needles are ground will almost never allow you to target a speicic part of the needle taper without having to settle for a change at some other part of the needle that I might want to leave as is. If I have an engine that fuels almost perfectly except at, let's say 2/3 to 3/4 throttle, and I need a different metering needle, one that is the same at all positions except the last few mm's before the end, they pretty much don't excist. If I have a 36mm Mikuni using a 6DH2 needle, and I only want to change the mixture at around 2/3 throttle but leave everything else the same, that needle doesn't exist, at least not in the standard Mikuni parts list. With either the Mikuni or Keihin I've found I have to spend a lot more time and buy a lot more tuning parts before getting the results I want. The carb of choice for me has become the Dellorto round slide, either the PHF or PHM. They are as sophisticated as either of the japanese brands, have accelerator pumps built in, and the needle assortment is, in my opinion, superior and allows tuning at specific needle positions without having to settle for changes along the rest of the needle length. I run these on my two 350cc racers and have fitted quite a few to Harley's and other motorcycle engines with extreemly good results. They're not as well known or as readily available as the Mikuni or Keihin, but the national distributor, Herdan Corp. in Pennsylvania, has never not had the carb or parts that I've needed and their customer service is as good as it gets. Again, I'm not knocking the S+S and have sold and tuned a lot of them. And I'm certainly not calling out either of the Japanese units. Have sold and tuned a lot of them as well. I've just found that at least with the engines I've worked with, I can get just as good a fuel curve in less time with less expense and hassle with the Dellorto. Others, of course, may have had a different experience.

Thanks for a detailed and well-explained first-hand recommendation of the Dellorto carbs and for pointing us toward the national distributor, Herdan Corp. in Pennsylvania.

enigma57 wrote: ↑Sat Jan 04, 2020 6:16 am Johnno, is this one of the 9-port Holden red engines? If memory serves me well, I believe the 215 cu. in. Rover V-8s did quite well with two 1-3/4" SU's or Zenith-Strombergs? If your inline 6 is near to this displacement, an alternative might be to work up an intake that will accept 2 SU's and position them so as to provide equal fuel distribution to the 3 siamesed intake ports.

Just a thought,

Harry

It is indeed a Holden 9 port. Triple SUs work very well on these engines, better than twins, and for anything other than a fairly mild build the 2" SU's make more power than the 1-3/4" versions. DCOE Webers seem to be the popular choice for circuit racing while SU's seem to have the edge for strip or street/strip usage. Single Holley 4 or 2 barrels are used as well, but distribution is usually less than perfect. The compactness and simplicity of the S&S appeals to me, hence the question.

oldjohnno wrote: ↑Sat Jan 04, 2020 4:16 pmThe compactness and simplicity of the S&S appeals to me, hence the question.

When a carb must fit inside a 45-degree V-twin and between one's knees, compactness and simplicity are paramount; on an inline six, not so much.

Johnno, I am working up a couple different intakes for my 9-port 292 Chevy inline 6 and was proceeding along similar lines until I ran into clearance issues. With LHD and both intake and exhaust on same side as driver here, I found that my steering column and brake master cylinder precluded any sort of triple sidedraught carburettor setup having proper trumpets and either individual air filters or drawing through a fabricated air box fed fresh air by ducting (trunking) with a remote filter positioned near cold air intake for the ducting. So at that point, I changed the focus of my intake development to the compact Weber DCNF twin throat carbs. This being a concession necessitated by engine layout and LHD clearance issues. Also, this carb being one I enjoy working with...... And having some good spares on hand with nothing else to use them on...... I went in that direction.

However, with your RHD setup there, you should have no such clearance issues and that leaves you many more options including sidedraught fitment, of course. As you noted...... With the right carbs, when running 3...... You can take full advantage of a straight shot right into each of the 3 siamesed intake ports.

That said...... Unless fitting triple SUs, I would suggest taking a long look at the Dellorto round slide carbs recommended by Heinz. He knows them like the back of his hand and I am sure he can point you in the right direction. His experience with midrange tuning parts for the S&S, Keihins and Mikunis leads me to believe that developing application specific stepped needles much like those used in Carter carbs to replace the tapered needles in the aforementioned carbs would need to be done in order to allow precise midrange tuning comparable to what he can do with readily available jets and needles for the Dellortos.

Regarding your intake manifold...... Are you fabricating this from scratch or utilizing one that is already cast similarly to what you need? It will make a great deal of difference regarding carb sizing and setup if you are using a simple log with side draught carb mounting flanges aligned with your 3 siamesed intake ports (shared common plenum)...... As opposed to 3 sidedraught carbs on an intake configured so as to isolate each carb and its paired siamesed intake runners (making the inlet portion of your inline 6 engine functionally [3] 2-cylinder engines). I would say that this would be the more efficient of the 2 designs and you could begin with 3 matched carbs, each sized and set up for same displacement V-twin motorcycle as each of your paired siamesed intake runners supply. That should give you a good baseline to work from. You might consider as well a small interconnecting tube joining all 3 otherwise isolated siamesed intake sections. This being a balance tube connected just downstream of each carb mounting flange. Not large enough to serve as a means of creating a shared common plenum as regards air/fuel mixture...... Small (say between 1/2" OD and 3/8" OD tubing) to smooth idle and slow running by balancing pressure in all 3 otherwise isolated carb sections...... Whilst keeping their respective air/fuel mixtures functionally isolated, one from the other.

Hope this makes sense and gives you some ideas. And if you are anywhere near the wild fires down under, do look to your safety. I have a friend in Melbourne NSW and she tells me the situation there at present is not good. Don't allow the fires to cut off your path of escape if it comes to that. Wild fires can move quickly and can change direction just as quickly.

Best regards,

Harry

A lot has to do with what you are willing to put up with re driving characteristics. All of these carbs can be made to run with a low pressure fuel pump. The S&S is somewhat rudimentary and will be nearly impossible to tune for decent mileage and run smoothly. The aforementioned Thunderjet can help it a little bit, but in my experience is just a main circuit that comes in a little later than the built in main. The Mikuni is going to be a much better carb than the S&S, but if you want performance like a 2" SU, then you would have to go for a 48mm Mikuni or a S&S Super D with 2.15 throat. Both are somewhat expensive and the S&S will turn your car into a bucking Bronco in normal traffic. The SU 1 3/4" would be closer to a S&S Super G or a 45mm Mikuni. The SUs probably won't come on as hard as the rest being vacuum operated, but are probably the simplest choice requiring the least amount of work to make run right. The rest will require time, effort and replacement parts such as jets and needles.

Hammer Performance, a Harley Sportster tuner ,has dozens of dyno readouts online...A modified 1250 cc Evo Sportster with one Mikuni 42HSR can support 110 HP at the rear wheel...The Mikunis are not harder to jet than other carbs...