One carb vs duals, theoretically speaking

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Maintaining fuel atomization is important to making power and is why wet fow benches and earlier attempts at stopping liquid fuel by using ink paid off in horsepower. Liquid fuel gathers on the wall when the port shape is not right and causes turbulence. Getting rid of the liquid fuel and hence the turbulence will allow better filling of the cylinder and a more homogenous mixture.

Changes in measured fuel mixture make minor changes in output power. An engine at full throttle will make nearly the same torque if the fuel mixture is 10-1 or 13-1. Combustion and exhaust temperatures dictate the needed fuel mixture more than power.

Modern street engines fuel mixtures are dictated by emissions and drivability. To meet emission standards the fuel must be added to each cylinder on a per stroke basis. The needed injector opening time is calculated individually for each cylinder on every intake stroke. The processor stays busy. Port fuel injection is the only thing that can maintain this tight of control over the mixture. Jim
 
We maybe need reminding at this point of Suzuki's Twin Swirl Combustion Chambers (TSCC) ?. In the early 1980s, Suzuki introduced this in their GSX1100 engines. Folks sometimes say you need a long stroke and small valves to produce good torque - this thing was a short stroke 4 cylinder with 4 valve heads - and put out more torque low down in the rev range than the same year Harley 1300cc (80ci) big twin. And the Suzook then went on to rev to twice the revs than the HD, making power all the way. Sidecar racers love this engine.

More to making power than just getting air into an engine any old how....
 
Single modern carb set up seems a very good idea for bikes which are ridden on a regular basis, with reliability and rideability being more important than maximum power. For max power, I would imagine an EFI linked to an inductive ignition system, with twin throttle bodies and a properly designed plenum chamber/air box, using a cylinder head with modified valve angles and re-shaped ports, would work very well.
 
Carbonfibre said:
Single modern carb set up seems a very good idea for bikes which are ridden on a regular basis, with reliability and rideability being more important than maximum power. For max power, I would imagine an EFI linked to an inductive ignition system, with twin throttle bodies and a properly designed plenum chamber/air box, using a cylinder head with modified valve angles and re-shaped ports, would work very well.
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Thats called a Ducati, isn't it ?
 
Rohan said:
Carbonfibre said:
Single modern carb set up seems a very good idea for bikes which are ridden on a regular basis, with reliability and rideability being more important than maximum power. For max power, I would imagine an EFI linked to an inductive ignition system, with twin throttle bodies and a properly designed plenum chamber/air box, using a cylinder head with modified valve angles and re-shaped ports, would work very well.
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Thats called a Ducati, isn't it ?
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The 749/999 and 1098 throttle bodies and injectors look pretty sexy, I almost scored some of the shower injectors off ebay, not really much space to fit them in the commando frame though, the ends of the throttle bodies I have point at the frame tubes.

Carbonfibre, what is the difference between having dual throttle bodies fed from a plenum (resonator) to having a single throttle body on the in let side of the same plenum and individual runners?
 
You can conect the dual body plenum to the cold air intake , and pressurise it . gaining B.M.E.P.

The Dcoe would produce near the output of the fuel injection , the econmy mightnt be as optimised , nor the ommissions .
but for raceing , or an existing machine its irrelevat , and it can be done in the shed if you have a few tools .

At Full throttle & Maximum r.p.m.s whowever , it wont make full Horsepower unless at the optimum mixture , ordinarily erring dry .
maximum torque requireing a bias damp / rich .Two Injectors , gee , we thought you meant per runner . four total . good idea .
Bends in the induction passages below four times the port dia. will impede effecency though seperation of the denser particals , fuel - inirtia .

Tuned induction on an unmodified frame , the carburators or throttle bodies fit in aft of the crade brace tube top braket / brace , to the top tube .
14 in valve to jet will get Mk 2 Amals in there if care is taken fabricateing the manifolds .The carbs should have the strap secureing as one unit .
Placement dictated by choke actuation . ( starting may be problematic without the choke function )

For us cowboys , throwing a D.C.O.E. or D.H.L.A. up in there is going to be equaly useful , a 45 or larger for circuit (track) use .

UNLESS sombodys going to go and fit a computor to the thing . Personally , a magneto would be more sense . on the Keep It Simple Principal .
 
I don't think 99% of forum members are remotaly interested in another 5 bhp at 7000 plus rpm, If BHP was in my interest i would take my commando down to a local dealer and trade it for a 170BHP gsx1000RR ,then i could get to my local a bit quicker...and guess what? No body would be slightly interested in it..Now take the MK3 and every one whats to chat....60 bhp or 65...its Bollocks!
 
i am going to replace my Amal Concentrics (2 x standard ones) on my '73 850 with the 2 x Keihin flatside setup from JS in California, anyone think of a reason why I shouldn't?
Regards Mike
 
Brooking 850 said:
i am going to replace my Amal Concentrics (2 x standard ones) on my '73 850 with the 2 x Keihin flatside setup from JS in California, anyone think of a reason why I shouldn't?
Regards Mike
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Nope.
 
I wish I did, not that there is anything with 1 mikuni, but those carbs sound good.

graeme
 
Don't be scared, you got plenty of money.
hehehe.
I have actually sorted the Amals out pretty well now, but am saveing for a set of PWK.
Figure I'll take them off (the Amals) and put them away where they can't wear.
 
AussieCombat said:
Don't be scared, you got plenty of money.
hehehe.
I have actually sorted the Amals out pretty well now, but am saveing for a set of PWK.
Figure I'll take them off (the Amals) and put them away where they can't wear.
Click to expand...

OKO's which are pretty much exactly the same as "PWK's" are $25 each, so and with the addition of a couple of flange to spigot mount adapters and a few jets, are likely to cost under $200............seems a bargain to me!
 
Carbonfibre said:
AussieCombat said:
Don't be scared, you got plenty of money.
hehehe.
I have actually sorted the Amals out pretty well now, but am saveing for a set of PWK.
Figure I'll take them off (the Amals) and put them away where they can't wear.
Click to expand...

OKO's which are pretty much exactly the same as "PWK's" are $25 each, so and with the addition of a couple of flange to spigot mount adapters and a few jets, are likely to cost under $200............seems a bargain to me!
Click to expand...

Except then you have to jet them correctly. Why don't you tell us the correct setup for an OKO and a Commando? :|
 
Carbonfibre said:
AussieCombat said:
Don't be scared, you got plenty of money.
hehehe.
I have actually sorted the Amals out pretty well now, but am saveing for a set of PWK.
Figure I'll take them off (the Amals) and put them away where they can't wear.
Click to expand...

OKO's which are pretty much exactly the same as "PWK's" are $25 each, so and with the addition of a couple of flange to spigot mount adapters and a few jets, are likely to cost under $200............seems a bargain to me!
Click to expand...

Carbonefiber, please send us the link to these OKO 32mm carbs. Please include the jetting requirements, needle dimensions, cable lenth and any particular needed to make these work.

By your firm opinion it is safe to assume that you yourself have done this and that the information is readily available.

What sort of mileage do you get?
 
Here is what Norton or any other twin cylinder engine manufacturer did when they supplied a single carb option as I had on my 1965 Atlas.
Inside each of the inlet ports were sleeves to reduce port diameter, this was to INCRESE the gas flow at low engine speeds. When I removed the single carb manifold to turn into twin carbs, I removed the sleeves, as they were no longer required.

I also found sleeves in the inlet ports on a single carb Bedford van with the 2.3, Vauxhall 8 valve engine. When I removed these sleeves and gas flowed the ports, yet retained the single carb manifold, the result was it would no longer cruise at 30 m.p.h. in top gear, as I had lost that low down power/torque.
Either way a single carb setup is usually slower on top speed than a twin carb setup.
That is basically the gist of it, you pays your money and make your choice, in todays high fuel cost climate I would go for a single carb set up unless you want power at any cost. depends if you want the power at the top end, or more power at the bottom.
 
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