On the bespoke air filters I have fabricated for the Super E—and the Super E design generally:

I noted a phenomenon with both of the filters I’ve made, but it’s been so long since I ran the OEM S&S teardrop cover that it may well have presented itself back then, too. That is, on warmer days when the bike is sitting after running at operating temp—like on errands—there is often a cloud of fuel vapor built up inside the filter element, requiring a couple of extra kicks to clear before the engine will fire.

It seems to me that the reason this happens is S&S’s design, which vents the float chamber directly into the air filter housing—inside the element—thus creating a cloud of vapor surrounding and inside of the carb throat.

Most side-draft carbs I have used over the years (I am thinking of the SUs I’ve modified for forced-induction running and the Mikunis I recently fitted to my ’71 Bonneville) have a float chamber vent that is attached to an external hose routed away from the intake manifold (and also the exhaust manifold on some engines). The purpose of an external vent is to avoid fuel vapor from a hot float chamber causing an over-rich mixture at startup.

S&S has an auxiliary vent plug, shown in the attached image (#14), but I need to find out where that passage leads to, as it isn’t clear from this image. If it leads directly to outside the carb body, that would solve the problem—but for the lack of routing vapor away from a hot engine.

However, looking at the casting in these photos, it seems like it might simply lead into the hole I’ve marked with an orange arrow. If that’s true, then I’d be right back where I started, only arguably worse, as the point of emergence would be immediately before the butterfly instead of an inch away from the throat’s opening.

The only permanent solution would be to drill and tap the casting to add a nipple to attach a hose that would vent the float chamber externally—i.e., without introducing a cloud of vapor into the throat just ahead of the butterfly, causing hard starts on warmer days when the engine is sitting while hot.

If I’m looking at these photos correctly, the tapped hole for the small nipple would go where the red arrow is. Then, I’d have to tap and plug or drift a flush (allen) plug into the existing vent.

Since I have to pull no 1 head next week to correct what I suspect is a displaced or damaged intake valve stem seal, I may well try this modification—which of course is reversible by simply inserting a threaded plug into the tapped hole I would drill for the nipple. But I think it’s worth it to try, as this is the only thing making the bike a joy to ride.

The only reason not to do this is if S&S intended to have something less than atmospheric pressure in the float chamber when the butterfly is at idle position or immediately after—i.e., before the butterfly is cracked open and vacuum in the manifold drops dramatically. That doesn’t make much sense though, because you want low pressure above the venturi to draw out fuel through the idle circuit and of course the venturi itself.

So, the only reason I can come up with for S&S to put the vent where they do is to avoid an external vent hose…. but why? For aesthetics?

 

S&S float chamber mod - continued:

Hmmm… but if I open up the auxiliary vent circuit, I’d not only have to plug the default vent hole; Id also have the even more challenging job of tapping and plugging the auxiliary passage in the carb’s throat.

So, it might be easier to simply tap and plug the existing vent hole in my bespoke base plate, and then either drill laterally into it somehow or drill into the default vent passage in the carb’s casting. I’ll see if the latter is possible, as it looks straightforward from the above L/H photo, when I have the carb in my hands, as it’s hard for me to confirm from the above photos.

But I’d like to skin this cat, as the only time I have to kick more than twice is when the bike has been sitting for a few minutes hot on a warmer day. I’d like to never find myself thinking about an e-start option if possible...

 

I believe what you have marked with the orange arrow is the opening for the enrichner in front of the throttle plate. That allows air and fuel to be pulled in with the throttle closed. The blow vent is the hole on the front of the carb that the air cleaner covers.

From the S&S (510-0251_super_eg_series_shorty_carbs) carb Picture 32 (below) shows main discharge air bleed metering jet.

Adjustable Air Bleed for Super E and G Carburetors. The main air bleed passage in S&S Super “E” and “G” carburetors is fitted with a replaceable .040" jet. See Picture 34. The replaceable jet allows changing the size of the main air bleed. Carburetors with this feature can be identified by a serial number that begins with the letter E or higher.

Notes
• The standard .040” diameter air bleed is the optimum size for most engine combinations, and should not be changed under most circumstances, regardless of intermediate and main jet selections.
• Changing the main air bleed size should be done only after determining a mid range driveability problem cannot be corrected by changing the intermediate and main jets.
• For tuning the main air bleed, S&SŽ recommends an initial increae from the standard .040” jet to an .048” jet as a starting point. Available jets and part numbers are listed in the S&S catalog.
• It is never necessary to reduce the size of the main air bleed below .040”.
• Shifting the start of main jet operation to a point higher up the rpm scale can lessen the effects of mid rpm driveability problems caused by mismatched cam and exhaust systems, but will not allow the engine to perform as well as it would with a well designed exhaust system.

 

Excellent, thanks for catching my error.

It looks like your keen eye has solved my issue altogether. The photo you added seems to show a carb where the auxiliary bowl vent plug has been removed. Compare your photo, added again here, to my photo, also reposted—and I’ve marked the same hole in both.

So, S&S’s default is to vent the bowl into the air cleaner housing adjacent to the carb’s throat—which isn’t working for the reasons I’ve stated—but the auxiliary vent option would vent to the atmosphere outside of the air filter housing (immediately behind it), which is exactly what I want. I guess due to the overflow with hose routed safely away from the engine, no chance of a fire when using their aux vent option.

Therefore, my task is easy-peasy: just tap and plug the standard vent hole in my bespoke housing, and remove the auxiliary vent plug from the carb.

Fantastic! I’ll report back on how that works. In fact this is so simple that I may try it this weekend, before the stuff arrives to fix the front valve stem seal issue.

 

The changing of the plug for the carb bowel vent is common for SnS carb when a T-jet is added. I've done it a couple times. In fact didn't do it once when adding a T-jet and the engine had a weird stutter to it when hot.. Took me a while to figure that one out..

 

Oh, okay, good to know. To my mind, so long as there’s a way for atmospheric pressure to enter the float chamber, I should be good to go.

In my blow-through, intercooled supercharger conversion for the A-Series, which requires modification of the SU HIF44 carb, I have people drill out a passage in the casting SU normally keeps blocked off for naturally-aspirated running (cheaper than buying SU’s ’turbo’ version). Then, the snorkel adapter & ram pipe I designed has a corresponding hole to transfer the pressure wave ahead of the carb throat (which is created by interchangeable rings that go into my adapter) into the float chamber—thereby maintaining low pressure above the venturi under boost conditions. (See attached pics.)

Anyway, the other part of the equation is putting a simple, one-way check valve in the float chamber vent hose, so air can be drawn in under NA running but boost is kept from escaping under boost conditions.

If you don’t do both things (I also have them reverse the butterfly shaft seals, a minor but helpful step), when you mash the accelerator, you’ll face plant on the steering wheel.

My point is, just noting that small things like bowl vents can have varied and sometimes significant impacts on driveability. So, I appreciate the help learning about the Super E.

 

I had mentioned last year that I favor the Brough Superior SS100 exhaust—the later model with both mufflers on the R/H side (1st pic). So, I bought some UK-style, symmetrical fishtail tips, thinking I’d someday get some of these Gasbox vintage Sporty mufflers before they sent them to chrome (they agreed to take a pair out of production at that point for me), and fabricate the muffler assembly and lower pipe.

But life intervened and I’ve yet to afford a TIG welder and can of argon (to make the interior of the pipe welds pristine), so this morning I decided to just fit the darned things and pivot them around and see what I got. Can’t get them quite vertical, of course, as my mufflers are directly centered above/below.

I first tried turning them parallel to the ground—like the tips tucked up under the rear bumper on the low rider Chevys around these parts—and that made me giggle. But anyway the subsequent photos show the tips rotated as far toward vertical as possible without contacting each other, which is actually not bad. It’s kind of a ’school of fish’ look, rather than two fish keeping their distance.

BTW - The tips do not extend past the tire (the angle of the first photo is deceptive), and the sound is not like the unmuffled Harley fishtails people like around here, and which I’m not crazy about: too raspy and ‘flat' f'or my taste. The wind’s blowing 45 mph gusts right now, but when things calm down over the next few days, I’ll fit the GoPro on the bike and putt around so folks can hear how they sound. It’s just a skosh quieter—not much—but the quality of the exhaust note is just a little less booming, I guess I’d say. Yet it has not lost that nice, throaty roar these modified Gasbox vintage Sporty mufflers produce on a 74” engine.

I’m eager to see what, if any, performance difference there is—though I’m still taking it easy, as I’m only up to 350 of the 500-mile initial ring-bedding process. I could always dremel out those little connecting pieces to improve flow a smidge if need be…

Anyway, GoPro sight-and-sound video when I get a moment. The experiment is totally reversible, but what fun to try!

 

That looks pretty good!

 

Thanks. Unconventional for sure, but like I said, partly an interim measure and the other part just curiosity about how they’d sound. I kept running across the box from the UK, pulling them out, and getting this urge to fit them somehow…

I do intend to complete the SS100 lookalike system—not just because of the aesthetics but because in building my ’71 Bonneville, and refurbishing my El Cheapo R100RS, I learned some reasons for the balance tubes between the mufflers.

Evidently, in the Triumph’s case, having a balance tube helped meet increasing noise restrictions, as each pulse is technically dispersed through two mufflers, at least to some degree. I don’t understand the back-pressure aspect very well, as there isn’t as much discussion about it. That is, whether a linked system can yield reduced back-pressure due to the staggered pulses with a 360-degree crank (which the Triumph has, too) and firing order, or whether a system of [x] diameter and [y] cumulative length ultimately has the same total back-pressure.

But as to total volume, it seems to me that a linked system would equalize the back-pressure somewhat, so that no. 1 pipe’s pressure would be reduced a bit…?

Anyway, I’m going to restart the conversation with Gasbox re: obtaining a pair of pre-chrome mufflers. And I see that they offer a collection of various 1-3/4” mandrel bends with which I could put together a bottom pipe of the right height to place the tips directly above and below each other, to achieve the narrowest possible setup.

Note: the ’31 BS SS100 cans do not appear to be flanged where the bypass pipes connect. Inside a can, the need for argon may be less important re: flow characteristics than inside a length of straight-line header pipe. But the resulting welds are much more uniform, so I guess it’s conceivable that there’d be less chance of cracking at that point when the miles start racking up….?

 

Nice clean look. They compliment the lines of the bike well.

Paul