Thanks very much for all the information--really great stuff, as I think that if indeed I do the dual-carb shuffle, I will use your X-head setup. Very cool!

On the carbs: I have Mikunis, though smaller and jetted for the 650cc power plant, on the '71 Bonny (in the photos in post no. 21 and 27, there were still Amals, sold to buy the Mikunis and a filet mignon to cook up for Sunday dinner). The Mikunis' attachment appears to be identical to the Dellorto 40mm, shown here. (These show the cable-operated choke, but you can get them with the 'flip lever' chokes, too.). Dellorto sells short 'manifolds' which have molded grooves to match those on the carb body casting. However, the 40mm Bings on my old BMW 1,000cc just used what appear to me to be slices of fuel-filler hose, and after being clamped on for a while grooves formed in the rubber.

Now, I should say that I need to measure the length and width of comparable Mikunis, as they appear to be far cheaper than Dellortos. The main difference appears to be that the Dells have an accelerator pump. But I also need to find out the availability of tuning parts for Dells, as Mikunis have a vast array of needles and jets available.

Manifolds: okay, good info on the runner length as extrapolated from plenum volume. As I've said--and I'll have to dig this up--there is extensive data people have compiled on intake runner length (and by implication, volume) and torque at [x] rpms. I know that Vizzard, the author of the definitive A-Series hot-rodding 'bible' did flow bench studies using various carbs, including dual-throat Webers--which on the A-Series meant one runner per carb throat but merging into two intake ports on the weird 'siamese' A-Series head. That's a whole other discussion due to valve timing and one cylinder 'robbing' the intake charge from the adjacent cylinder via the siamese port--and which wouldn't apply to a one carb-per-cylinder Sporty setup.

But the runner length impacting torque output at [x] rpms would apply. So, I'll bone up on this (the old slant 6 American auto engines used long runners to good effect, as did the 2,000 Toyota Camry 4-cylinder, etc., etc...). At any rate, as you point out, two carbs may be a wash re: ultimate performance, but that isn't the primary criterion for this project--and especially in view of your experience with the dual carbs at least not being counter-productive, the other criteria which do matter to me may favor trying this out.

Those criteria are: (i) maximizing narrowness of the V-twin engine & netting knee-to-tank riding posture (I hate the R/H bow-legged posture); (ii) having a unique Ironhead hot-rod; (iii) novel tinkering/fabrication challenge.

Finally, I'm thinking that I'd use short rubber pieces to connect the carbs to aluminum runners, and to connect the runner to the head's intake port. This could produce several benefits. First, I could weld mounting tab onto the runners, so they would be relatively solid and stay in place (with loctite, of course!). Second, fabricated aluminum runners means I can position the carbs in optimum position for criteria no. 1 above. Third, I can sand (and if I wanted to, polish, powder coat, or...?) the aluminum runners to match whatever aesthetic the bike ends up with. Fourth, I could also run a flex hone through the inside to produce a really nice flow.

As for your race bike, wow... a sub 10-second quarter is fast. When I was growing up here in ABQ, South Eubank used to dead-end into the landfill. So, it was then a l-o-n-g straight, lonely blacktop on the southeastern edge of town (terminating near the AFB fence line), and we troublemakers used to head out there on Saturday nights to drag race. I was 15 going on 16, with no money and fledgling mechanical skills, so I either rode along or handled the official starting lights (two flashlights). There would be a long line of cars with kids sitting on the hood, sipping beverages (strictly non-alcoholic, of course!), with the headlights on to illuminate the proceedings.

I vividly recall a Camaro that nearly side-swiped me when the tires lost traction, but when warmed up was achieving something like a 13.5-second quarter. One night, he was stomped by (wait for it...) a Chevy van! It was called "Iron Butterfly" (google it), and the blown engine when the headers were uncapped was running 13 flat and on cool evenings maybe a hair better. When that thing went by me, gripping the flashlights and gritting my teeth, it felt like Muhammad Ali was hammering on my chest with both fists and someone was banging trash can lids beside my head.

Then, someone would shout a warning and we'd look north down the road at the 'cherries' flashing in the distance, and people would scatter, dirt flying, engines racing, cars and trucks bouncing across the mesa or rolling at 3 mph under the speed limit up the road toward the oncoming cops...

Anyway, sub-10s are freakin' fast. I can't imagine holding onto the handlebars--but I assume you had a seat that kept the rider from ending up on his butt at the starting line, watching the bike careen down the strip...

 

Well, gosh darn it... that $2,500 Ironhead sold--and I'll bet for less than that. Should've jumped on it...

If anyone sees a good donor bike or engine, please lemme know!

 

1984 Harley-Davidson XR1000 | eBay

 

On ncarbs...Need to remember you need the same size with One manifold or One Each!! each cylinder is Drawing its air thru the Carb...One at a time..two are Never really fed at once! We used rubber ends on Aluminum tapered tubes..for manifolds.
That Particular Iron head was a Hoot...and I never get tired of showing off pictures of it..

 

Yeah, if only I had that much bread....!

 

Good point. 'Charge robbing' isn't an issue with a 360 crank and two cylinders...

Now that is a classic shot. Worth this entire thread to get that one posted!

I'm really bummed that the late-model, low-mileage Ironhead in Nevada got away, but as I've said at $2,500 plus $1,000 for transportation, my shoestring budget would've been blown to crud. I think the sweet spot is going to be a NM, CO, AZ or TX bike, probably later model to avoid the premium that earlier pristine models seem to fetch, as the half- or one-day drive with my utility trailer will keep costs down and leave room to negotiate the bike itself to generate that 'sweaty palm' syndrome. My neighbor says his turbo 6-banger Dodge pickup gets pretty good mileage at steady highway speeds and will hardly feel my utility trailer behind it, so the diesel shouldn't be too bad...

 

FWIW, you can rent a u-haul motorcycle trailer for $15/day. Has a built in wheel chock and ramp for loading. It was worth the money when I picked up my last bike five or six hours away.

 

I have one I mostly just fire up once in a while to listen too.

 

Here's mine.

 

I would decidedly Not be pursuing a low mileage mostly Stock Example for modification...gonna modify anyway,..cheap old Neglected Ironheads are out there...actually literally Everywhere.. Mostly have Not gained much value in 20 years..
This Aint Panheads, nor Shovelheads we are talking about!!
Hell...Get on market place and get one Found right around the Corner..