Possible to run a single carb?

[memper]

Just for shits n giggles Im curious to know if a single carb like an S&S could work assuming a custom manifold was made. Or does nothing really match the performance of FCRs?

[Dry Martini]

Run? Yes. Optimal? No!

[Speeddog]

I suspect if you talked to a couple Paso wingnuts, one would likely *give* you a Weber carb/manifold setup.

[brad black]

i was thinking it might help a 400, but i think it's just too much fab time required for me to try it on mine.  i don't know that it would neccesarily hurt it.  thinking about it, reasoning below.

if the horiz inlet opens 15 btdc and closes 70 abdc (1mm lift), the vert inlet opens 270 degrees later which is 75 abdc horiz which is as the valve is just less than 1mm open.  so the vert may benefit from the flow already coming through the carb maintaining some of its momentum.  maybe.  but i can't see them charge robbing at all.

the horiz opens 450 degrees after the vert, so the flow will have stopped by then no doubt.

manifold design is probably the biggest hurdle, but it could be done.

it may put a stronger vac signal on the carb in general, which might help the low speed response and general response from a closed throttle.  which would help reduce the need for an accelerator pump.  maybe i'm hoping too much on that one.

i wouldn't go bigger in size to start with.  but it could work.  try it and see.

[memper]

I just know that older HD motors run very well on one big carb. Granted the HD engine is very different than my m750. My reasoning was centered around aesthetics and the *possible* ease of tuning (1 vs 2).

[Dry Martini]

I just know that older HD motors run very well on one big carb. Granted the HD engine is very different than my m750. My reasoning was centered around aesthetics and the *possible* ease of tuning (1 vs 2).

Yes but no better than the XR750 Harley flat track bike or the XR1000 race bike. Those bikes have dual carbs and a different intake arrangement.

It also improves their perceived liability. Can you imagine the typical Harley knuckle dragger bolting on two carbs and trying to get it to run well? They have enough trouble with getting one setup properly.

[JoeB]

You'll have problems with reversion using a single carb and manifold. The manifold design will need to be correct for volume / length and the plenum size.

Then jetting a carburettor correctly, matching air correction jets and emulsion tubes, is going to end up costing you more than the original outlay for a high performance FCR setup, or dare I suggest it…  Electronic fuel injection.

In this day & age, I do not understand why you would bother going backwards in design / efficiency.

You could reprogram an ecu from a later model 2 or 4v engine, use the throttle bodies and gain a truckload of fuel efficiency and rideability from it.

and that would probably cost the same as an FCR kit too...

plenty of options, but a single carb is really something that belongs on a stationary engine, or a Harley. 

[Langanobob]

One of my bikes is an old Triumph twin, not one of the new Triumph  bikes, but built back in the days when Britain ruled the seas.   Triumph made two versions of their vertical twin, one with a single carb and one with dual carbs.  The single carb version (Tiger) was quicker out of the hole and the dual carb was faster top end but only barely faster.   The main advantage of the dual carb model was the bling factor.  Although it was probably termed something like "snazzy" in those days. 

Of course comparing the performance of a single carb Triumph twin to a Ducati twin with a single carb is apples to oranges.   The Triumph vertical twins were long stroke pushrod engines, designed for low speed torque (or maybe what was high speed power at the time, but considered low speed torque now) and couldn't really take advantage of the additional air/fuel flow from dual carbs.  And, the intake arrangement for a vertical twin is pretty simple compared to the plumbing necessary for a single carb on a Duc engine.

I personally don't see the attraction, especially the esthetic side of it, unless for some reason one wanted to own a Duc that  looked like a Harley.   Beauty being in the eye of the beholder,  I'm all for out of the box thinking and  doing it and getting it close to right would be an educational process.  I'm with Brad that if you want to, go ahead and try it.  Not like it's an irreversible change.  The real consideration that comes to mind is the possibility of one cylinder running too lean and running hot.

Bob

[Langanobob]

I suspect if you talked to a couple Paso wingnuts, one would likely *give* you a Weber carb/manifold setup.

I didn't know Paso's are single carb?   Do you know what the reasoning was?   Never owned one a new Paso on the showroom floor caught my eye and was pretty much what got me interested in Ducatis.

Bob

[Howie]

The carb used on the Paso was a Weber DCNF, a 2 barrel carb, both barrels identical, one barrel for each manifold.  Our carby monsters have 2 carbs that are mated together, so not that different.  Big difference is the Weber carb Ducati used was not constant velocity, as commonly used on motorcycles.  They were probably too big for the engine, being 44s  I know someone who runs a 40 on his Paso.  More or less power?  Dunno, but throttle response is much better.

[Langanobob]

Thanks Howie.

[krista]

Interesting!!!

I'm starting to work on Pongo again... was the crazy 104hp 904 bored 3mm over with MBP heads and FCR singles. I have since parted out the go-fast parts and found out that the crankcases were cracked.

Soooo... 3 or so years ago I got a 750 engine on the cheap, so it is going in Pongo and I'm making Pongo run again.

And now, back to this thread. I was thinking I really don't want to put stock Mikunis on it. And it's a 750, so dual FCRs are kinda a waste. Next idea: hey how about a single FCR?! Like on Hardley Ablesons!  And I'm googling and find this relatively current thread. And fuel injection is mentioned...

Oh hmmmm... I've got a TON of fuel injected junk laying around in my shop. And embedded controller stuff. So why not build a single throttle body efi system for it!

I'm so screwed...
Chris

[brad black]

now there's an idea.  let's take something simple and overcomplicate the complete make the beast with two backsing shit out of it.

i still think the single 38 has merit on a 400 at least.

not that i'll get to try it.

[Cloner]

Gotta love that Aussie sense of humor.   

As to the Paso, I rebuilt the carb on a 906 late last year and it was one of the smoothest running carbureted Ducatis I've ever ridden.  Strong?  No.  Fast?  Absolutely not.  But it's a touring bike as far as I can tell, and for that it'd be a blast.  It's damned comfortable, to boot!

[krista]

Hahahaah! That's awesome. At the least I'll try to come up with a Y manifold. I'm pretty sure one FCR (or a Harley carb) can more than handle the M750 engine's output.

The more I thought about the EFI, the less I want to go that way...
» Will need a throttle body with TPS, injector mount, and cable on it.
» Will need a signal for the ECU.
» Figure out the base map, then tune accordingly.

And actually I thought of the answers to these:
» A HM1100 throttle body sets I took apart has the cable and injector mounts & I should be able to graft a TPS on it and make that work. I've got lots of experience dicking around with TPS making my test bench for them.
» This will need testing, but I can keep the kokusans and wrap a wire around one of the spark plug cables. The Arduino should be able to catch that pulse.
» The next issue is how often to fuel. The throttle body/EFI can act like a dumb carburetor and just feed fuel to the intake tract. Even though the pulses on one cylinder are timed perfectly, if I dump fuel into the intake with each trigger (remember it uses wasted spark, so it'll fire every crank rotation), then it might well behave. Not multiport at all, but if it works??
» For tuning, I could install a EGT sensor and monitor that ... probably that would work best only near idle?

And I read a couple links about Arduino's and home made EFI. Seems do-able...

So I reckon the next step is to come up with a Y manifold to start with. I'll make it so EFI or carbs will work... and go from there.

Chris