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Recently I have seen a bunch of dual carb Flatheads, Knuckles and Pans. They modify the intake port to go 90° from the head and stick straight out from the motor. I have seen Flatties with both on the same side, also seen guys running on on each side. Exhaust pipes remain stock locations. Can be done for sure. Just need to be brave enough to cut **** up and skilled enough to weld it back together. Oh then be able to tune the beast.
Eighteight - you're right that there's very little clearance between the front cylinder's inlet tract and the rear exhaust. Maybe when you're blasting along it's no biggie, but slow-and-go might be nightmarish. And I'll bet the float bowl would be literally boiling after stopping for gas or a burger.
Architect - Hmmm, well indeed if one put the front carb on the L/H side, swept back, or the rear exhaust on the L/H side, there'd be no issue. Or...
BTW, I like the split rockers. Looks kinda like a Brough Superior.
Seems like a fun project and an engineering challenge. I might start hunting around for an Ironhead and see if I can find a place in the garage for one. Not necessarily in that order.
I ran across this two-episode history of the Sportster.. by a Brit. It's actually not bad. The link is to espisode 1, and you'll see the other in Youtube.
Okay, actually multi-part--and quite a lot of historical context (which you can skip through if you like, to get to the part about the bike). This claim is amazing, but he says that in 1965, the 883 XLCH was the fastest production motorcycle in the world at 122 mph. I'll be darned.
They don't say anything about how to accomplish the swap. Just mention Andrews DX racing cams, which are still made for Sportys.
But since Sportys have 4 individual cams, perhaps it's as easy as switching them around? I notice one has what I assume is the tach or dizzy drive gear on it(?), so there's that consideration. But if the two rear cams don't have that feature, maybe you just swap them and then time it...?
I think it could indeed be done--and with a magneto ignition to avoid the necessity of space for a battery, and a custom oil tank so the rear carb could be tucked in nicely via a handmade manifold (with another for the front carb), it could be an elegant-looking, functional setup... and go like the devil.
My apologies for the Photobucket overlay, but here is an example of precisely what I'm talking about--or very nearly so, re: the manifolds and degree of tucked-in air cleaners. (P.S. - the builder claims 331 lbs dry... ah, um, no.)
Also, I wouldn't do the traditional cafe thing re: the tank and tail piece, mufflers and aluminum wheels. It'd be more like the 1930s racing bikes in many ways.
Really fun to think about all of the engineering and stylistic choices, but I do think an earlier Ironhead--with kick-only starting to save weight--is the ideal powerplant to build outward from.
This is a once-and-future project, and who knows if I'll kick the Photobucket before getting to it. But the sort of thing that helps me 'count sheep' at night and makes me want to get up in the mornings.
First - how many Ironhead riders are over 6' tall and somehow don't feel too cramped on their bikes? I had an '86 and it was a bit small for over-the-road travel but was fun for zipping around town--but I'm not into Evos so got bored with it.
Second - and getting to the main point of this thread, I'm attaching this photo not to discuss the overall build, but just one aspect of it--the dual carbs.
I understand from the article that the guy used two front heads to fit dual carbs angled backward--so they don't poke you in the leg, which I find very cool on a compact bike. I think I've seen flat track vintage racing Sportys with dual carbs, so presumably they do the same thing--fit two front heads. Making up an exhaust and intake manifolds seems straighforward. But how do you resolve the camshaft situation? Are there other considerations and fitment issues?
I would appreciate it if someone who has actually done this conversion could list which parts you'd need and the changes one would need to make it work. Take a '68~'70 Ironhead engine as an example. I think it'd be a fun project but would like to know exactly what I'd be getting into.
Thanks for any help.
What if you were to run a front jug installed as the #2 jug, and the rear jug installed as the #1 jug? Wouldnt that make sense if you wanted two carbs so both carbs would be on the outer sides. I would think how they have it set up as two fronts like in the picture that the now #1 jug's carb would have a lot of heat issues like having the fuel evaporate or boil inside the carb and nit working properly, but if you used a rear jug placed as #1 the carb would be in the very front of the engine and away from the exhaust and the heat, and itd be further forwards so itd be away from your leg as well.... Id worry more about the carb in the back burning you and would think youd have to modify where it is positioned..... Or what if you turned the rear jug 180° and used it as #1 so you could have a left and right exhaust pipe, and the carbs would both still be in the middle but facing opposite ways. Wouldnt you just have to resize valves for rear jug that is now #1 jug and 180° the timing so the intake valves could now be exhaust valves and vise versa? Because thatd be sick to have opposite facing carbs with there own intakes and staggered opposite sided exhausts.
What if you were to run a front jug installed as the #2 jug, and the rear jug installed as the #1 jug? Wouldnt that make sense if you wanted two carbs so both carbs would be on the outer sides. I would think how they have it set up as two fronts like in the picture that the now #1 jug's carb would have a lot of heat issues like having the fuel evaporate or boil inside the carb and nit working properly, but if you used a rear jug placed as #1 the carb would be in the very front of the engine and away from the exhaust and the heat, and itd be further forwards so itd be away from your leg as well.... Id worry more about the carb in the back burning you and would think youd have to modify where it is positioned..... Or what if you turned the rear jug 180° and used it as #1 so you could have a left and right exhaust pipe, and the carbs would both still be in the middle but facing opposite ways. Wouldnt you just have to resize valves for rear jug that is now #1 jug and 180° the timing so the intake valves could now be exhaust valves and vise versa? Because thatd be sick to have opposite facing carbs with there own intakes and staggered opposite sided exhausts.
Huh... I guess that I'm too unfamiliar with the cylinders to know if you can rotate them 180°. But I agree that the way this guy has the front intake manifold immediately adjacent to the rear exhaust pipe is no good. I also don't like the positioning of the front carb's mouth, which would try to suck your pant leg into the ram pipe.
Now, a forward-facing front carb is intriguing--well, or I guess a forward-fitted front carb. The intake manifold, air box, and/or orientation of the throat would have to be worked out, but that'd be fun stuff to address.
I still have yet to dive into the research to figure out whether you can switch the cams around, and how that is reconciled with their drive mechanisms and valve timing. I've been immersed in getting my '71 Triumph Bonneville cafe bike on the road, and someone sabotaged my '51 Pan-Shovel outside the store where I was shopping, such that it now needs a complete rebuild (they cut the oil feed line). So, the order of projects got re-ordered unexpectedly...
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