Single carb anyone?

[dazbaby]

Hi All,
I am about to purchase my second GS and I am keen to modify it, perhaps not in the obvious way i.e. to go faster, but more along the lines of getting more mpg. Years ago, a lot of British bikes were twins which had only one carburretor and I am thinking of going down the same avenue with mine if possible. The idea being to get a little more torque and grunt lower down, combined with better mpg abeit at the expense of top end power.

Has anyone got any experience of this......could one of the original carbs be used with bigger jets, can one of the original carbs flow enough fuel / air or will I require a bigger one and does anyone know of a company which could manufacture an inlet manifold to suit?

I would imagine a GS set up in this manner would give excellent economy.

Cheers in advance.

Darren  

[ecpreston]

what's the theory behind a single carb providing better fuel economy?    Seems like you could choke off and lean out the two existing carbs just as well and achieve the same thing.

[The Buddha]

OK lets see here. A carb sits idle 75% of the time. A carb works to its max potential only in WFO throttle and even so only in the 10% of the cycles.
A single carb will do nothing, a smaller carb will be more fuel efficient but kill the higher throttle openings. A longer or more twisted without impacting velocity manifold will also be more fuel efficient but more than likely at the cost of top end.
Brits put a single carb in cos they figured it was cheaper to make a Y manifold than a twin carb set. You need the air box to cut down on the air as well, you fit a single carb on a Y manifold and slap a K&N on, there goes any efficiency.
Essentially its this - you cannot just cut down on the fuel that is going in. You need to feed it that 12.5 to 14.1 (if I remember) ratio. The thing you have to cut down on is the air then you can cut fuel too.
Samller carbs yea will work, cos they cut off the air. The limitation in any carb is air. Not fuel. If you took a perfectly jetted carb from 1 bike and moved it to another of different displacement, it will be jetted perfectly but will either be too small or too big ... or perfect.

Like a 750 GSXR with perfect jetting will run on a 1100 GSXR without any jet changes, any changes at all (BTW these 2 were so close they sent them out with 38 and 36mm carbs in US, 38 and 38 in canada and europe and some years of 750 got 40mm). But that is mainly cos the peak flow of those 2 were pretty close. If you run it on a bike that didn't ahve that much peak air flow the carb will act like its too big. Like you're at 3/4 throttle and you are at max speed for the bike, more throttle will do nothing ... and if its too small then you'd hit full throttle and then bike will not have attained its highest speed. but where it runs in both cases it will run perfectly.

Anyway to get back to your 2 into 1 intake - I doubt you gain anythng at all unless you go smaller/farther/twistier ... cut down on the air.
Cool.
Buddha.

[ojstinson]

Trade your GS in on a Honda Nighthawk CB250, it's a twin with one carb, gets 75-80 MPG, tops out at 75MPH, is practically indestructible ( I know a guy that put 140,000 miles on one ),  looks pretty decent---and brand new they are half the price of a new GS.

[fred]

I think you'll find things like final drive ratio and rider habits will be the easier mods to get better gas mileage. I think you'll find that a very well tuned engine, a larger front sprocket and more conservative use of the throttle will be your friends.

[bobthebiker]

simply put, the time, money, and headaches you'll go through trying to make a 2:1 intake with 1 carb work isnt worth the hassle for what you'll get from it. changing how you ride and gearing will make more difference and be much cheaper/less frustrating.

[ohgood]

I think you'll find things like final drive ratio and rider habits will be the easier mods to get better gas mileage. I think you'll find that a very well tuned engine, a larger front sprocket and more conservative use of the throttle will be your friends.

+1

[The Buddha]

simply put, the time, money, and headaches you'll go through trying to make a 2:1 intake with 1 carb work isnt worth the hassle for what you'll get from it. changing how you ride and gearing will make more difference and be much cheaper/less frustrating.

BTW this is a common if not downright easy and everyone does it type of mod in the virago.
1 time pulling the carbs will pay off for the whole damn thing. I am debating on mine right now. But I made some mods to it. I can yank a carb off the virago in 9 mins (my record and it ended with many hurt and skinned knuckles - I ahve pics I put on the virago site, 9 mins with in fact over 8-10 pics) and back in, in 15.
My leisurely pace is ~12 mins for out and 20 for in. Honestly people who charge 80 bucks an hour and call a carb removal on one of those bikes as a 2-3 hour job should be lined up and shot. You pay for expertise, and 80 bucks oughtta buy you a lot of that.
Anyway, a 2 - 1 is a mod for some bikes that shows some improvement ... and virago's especially 1100's show ~10-20% bump in gas mileage, a great improvement in low and mid and it costs them WFO performance - all as expected.
Cool.
Buddha.

[Pigeonroost]

maybe get Edelbrock to make you a manifold for a 650 CF Holly to fit the GS500.



prs