An intriguing question...?
#1
09-10-2008, 02:08 AM
An intriguing question...?
I am sure you have all noticed that motorcycles tend to have one carburetor per cylinder. Has anyone stopped to questioned why? This query of mine has been one I have come to ask whenever it comes to mind to do so. I seem not to be able to get a straight answer or a logical one at that. The general retort tends to go something like this: "Well thats because thats what motorcycles are s'pose ta have" or simply "Because they're motorcycles", and of course the elaboration ends there. I have googled the question sparingly but to no conclusion.
It would seem that a single carburator would not only be ownership friendly but cost efficient as well, not to mention the wieght that would be saved. As a former yet proud owner of a Detroit mopar, I have seen conclusive evidence that a single carburetor is sufficient to power a demanding powerplant, or are the circumstance different? I have read in a few documentaries on the history of motorcycles that at one time it was standard for inline engines to have one carburetor. So, why is not the case in these times? Looking introspectively hasn't been too productive either amid this plethora of condescending opinions and unvalidated ideas as you can understand.
I am looking forward to get an answer, but be sure you substantiate it.
An inquisitive bike,
volvo9de40
It would seem that a single carburator would not only be ownership friendly but cost efficient as well, not to mention the wieght that would be saved. As a former yet proud owner of a Detroit mopar, I have seen conclusive evidence that a single carburetor is sufficient to power a demanding powerplant, or are the circumstance different? I have read in a few documentaries on the history of motorcycles that at one time it was standard for inline engines to have one carburetor. So, why is not the case in these times? Looking introspectively hasn't been too productive either amid this plethora of condescending opinions and unvalidated ideas as you can understand.
I am looking forward to get an answer, but be sure you substantiate it.
An inquisitive bike,
volvo9de40
Last edited by volvo9de40; 09-10-2008 at 02:11 AM. Reason: gramar
#2
09-10-2008, 04:49 PM
Join Date: Sep 2006
Location: La Costa, CA
Posts: 807
I can't substantiate it with theoretical knowledge, but I have plenty of the empirical kind.
My first bike was a '93 Sportster 883: one large carb feeding two, big air-cooled cylinders. The bike got 50mpg if I rode it gently OR if I rode the pi$$ out of it, (though it has considerably less **** than our 500R.)
The one big advantage the Harley had was intake turbulence! The rapid oscillation between the two intakes meant pretty solid fuel atomization in stock form. I had a lot of fun with that bike because everyone in Southern Colorado was getting their intake tracts machined smooth and even polished on their big-twin Harleys.
On the surface, it seems reasonable that smoothing the intake tracts would allow a greater intake flow rate, but that doesn't take into account the intake turbulence, intended by those engineers who intentionally designed sharp edges and course surfaces on the aluminum tracts.
Less turbulence = less fuel atomization = poorly carbureted 'globs' of fuel making it to the chamber, which didn't combust as energetically or as efficiently as it should.
The result was that my bone-stock 883 Sportster was competing with (and frequently beating) these 1370-cc, heavily modified Harleys! Of course many of these guys accused me of running a 'sleeper' 1200cc in 883 disguise, and I just assumed that I got one of the stronger bikes from the factory. (Until I learned the real reason, haha.)
The biggest advantage that single-carbed Harley had was low-rpm torque. But it quickly got winded at higher rpm. I've had my 500R up to about 125mph, but the fastest I ever got that 883cc Sportster was 110; chin on gas-tank, WFO, and even going down a slight grade--the bike would go no faster.
But that Harley needed that extra low-end torque, because multiple carbs also give noticeable quicker throttle response. I assume this is because of the huge volume of area necessitated by joining two cylinders into one carb. A smaller volume (with a more direct, but still turbulence-inducing path) means more immediate throttle response.
About the only down-side to multiple carbs I can think of is that you have to synchronize them occasionally, so that they are working equally. But a $50 vacuum meter and a screw driver is all you need to enjoy balance and efficiency, so meh.
I just got my motorcycle mechanic's textbook back from a friend who'd forgotten to return it. I'll have to look this up...
Good question.
-CCinC
My first bike was a '93 Sportster 883: one large carb feeding two, big air-cooled cylinders. The bike got 50mpg if I rode it gently OR if I rode the pi$$ out of it, (though it has considerably less **** than our 500R.)
The one big advantage the Harley had was intake turbulence! The rapid oscillation between the two intakes meant pretty solid fuel atomization in stock form. I had a lot of fun with that bike because everyone in Southern Colorado was getting their intake tracts machined smooth and even polished on their big-twin Harleys.
On the surface, it seems reasonable that smoothing the intake tracts would allow a greater intake flow rate, but that doesn't take into account the intake turbulence, intended by those engineers who intentionally designed sharp edges and course surfaces on the aluminum tracts.
Less turbulence = less fuel atomization = poorly carbureted 'globs' of fuel making it to the chamber, which didn't combust as energetically or as efficiently as it should.
The result was that my bone-stock 883 Sportster was competing with (and frequently beating) these 1370-cc, heavily modified Harleys! Of course many of these guys accused me of running a 'sleeper' 1200cc in 883 disguise, and I just assumed that I got one of the stronger bikes from the factory. (Until I learned the real reason, haha.)
The biggest advantage that single-carbed Harley had was low-rpm torque. But it quickly got winded at higher rpm. I've had my 500R up to about 125mph, but the fastest I ever got that 883cc Sportster was 110; chin on gas-tank, WFO, and even going down a slight grade--the bike would go no faster.
But that Harley needed that extra low-end torque, because multiple carbs also give noticeable quicker throttle response. I assume this is because of the huge volume of area necessitated by joining two cylinders into one carb. A smaller volume (with a more direct, but still turbulence-inducing path) means more immediate throttle response.
About the only down-side to multiple carbs I can think of is that you have to synchronize them occasionally, so that they are working equally. But a $50 vacuum meter and a screw driver is all you need to enjoy balance and efficiency, so meh.
I just got my motorcycle mechanic's textbook back from a friend who'd forgotten to return it. I'll have to look this up...
Good question.
-CCinC
#3
09-10-2008, 06:14 PM
I can understand why V-twins benefit from it, but never understood why my Ninja 250 with a parallel twin needed two carbs.
When cylinders aren't parallel, it would be much harder to make the path from the carb outlet to both intakes equal in length. It's possible, but difficult. This could affect throttle response.
Parallel twins don't present that problem.
When cylinders aren't parallel, it would be much harder to make the path from the carb outlet to both intakes equal in length. It's possible, but difficult. This could affect throttle response.
Parallel twins don't present that problem.
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