Anyone run a single carb?

[kyle.quamme]

They all came this way from the factory. Most were snowmobiles, but I had a Triumph (650cc) and my Harley (1000cc) are also this way. Yes they all ran pretty good for what they were. Nothing by todays standards. Most of your carb'ed cars were this way as well.

I currently use a single 42mm Mikuni on my race bike.

Do you think I'm going to need that big of a carb to get the neccessary flow for a 550?

[Dan Ruddock]

Single carb, not a good idea. You will have to run very mild cams or it idle like a pop corn machine. Single carbs are for tractor engines like a harley. Dan

[KGB]

HAHA, more or less for a CC reference, since most HDs run a single carb setup from the factory, heck I dunno of an HD model that doesn't come with anything but a single carb.

The 883 head from the factory is almost pefect as far as flow goes.
Jerry Branch actually uses(d) a 883 head on the 1200cc motor, due to the better flow rate.
Something to keep in mind, flow rate and we/you have 4 valves?
As stated CFM, cubic feet per minute is your concern.
The Triumph 500cc family had a single carb, dual carbs were an option, back in the late 60's early 70's. How much more HP? Not sure but enough to earn the label Daytona!

So what is the bottom line on this idea?
Just because?
or ease of tuning and ridablility ?

[lecroy]

Do you think I'm going to need that big of a carb to get the neccessary flow for a 550?

There's an easy way to find out.

[kyle.quamme]

The 883 head from the factory is almost pefect as far as flow goes.
Jerry Branch actually uses(d) a 883 head on the 1200cc motor, due to the better flow rate.
Something to keep in mind, flow rate and we/you have 4 valves?
As stated CFM, cubic feet per minute is your concern.
The Triumph 500cc family had a single carb, dual carbs were an option, back in the late 60's early 70's. How much more HP? Not sure but enough to earn the label Daytona!

So what is the bottom line on this idea?
Just because?
or ease of tuning and ridablility ?

for the ease of tuning, as long as the loss in HP is not too much, then i don't care all that much, i just want a setup that is easy to maintain and service.

[lecroy]

I had a T120 and a TR6. The TR6 was a 650cc and had a single Amal carb that I doubt was over 30mm. My Harley is 1000cc and came with a 42mm but now has a 36mm Mikuni and runs pretty good with it.

[kyle.quamme]

I had a T120 and a TR6. The TR6 was a 650cc and had a single Amal carb that I doubt was over 30mm. My Harley is 1000cc and came with a 42mm but now has a 36mm Mikuni and runs pretty good with it.

But the issue has been brought up about the CFM of a Harley vs the CFM of an inline 4, and consensus is that the inline 4 will pull a lot more CFM. Maybe start with a 38mm Mikuni and go from there?

[Commodus]

But the issue has been brought up about the CFM of a Harley vs the CFM of an inline 4, and consensus is that the inline 4 will pull a lot more CFM. Maybe start with a 38mm Mikuni and go from there?

No, that seems like the wrong way to do it. Instead, there must be a way of simply measuring the CFM your engine is using. I bet there is someone on this site that could tell us.

[kyle.quamme]

No, that seems like the wrong way to do it. Instead, there must be a way of simply measuring the CFM your engine is using. I bet there is someone on this site that could tell us.

On Vintage-Suzuki.com, they have a VM 38 for a 460cc I believe, and a TM 38 that they say should work on a 500, so i dunno for sure, but I'd think something in the 38-40 range VM style would work, the thing would be getting it to work perfect.

[Commodus]

On Vintage-Suzuki.com, they have a VM 38 for a 460cc I believe, and a TM 38 that they say should work on a 500, so i dunno for sure, but I'd think something in the 38-40 range VM style would work, the thing would be getting it to work perfect.

Yeah, but as drhermanstein (I think that's right) says, displacement isn't really the issue. And carbs are expensive, so you probably wanna get it right the first time.

AND I'm really interested in the answer, heh

What size is your engine? Is it a GS550 four?

[49er]

Have you considered using a single twin choke, side draught carb like a Dellorto or Weber.

The advantages of using such a setup are:

1. You get a strong scavenging pulse between 1&2 and 3&4 inlets, as the inlet timing is always 180 degs seperated at each branch.
2. It is easier to fabricate a manifold that keeps the inlet tracks at the same tuned length, than for a single choke carb setup.
3. From your CFM calculations, you can further calculate the choke diameters required to deliver optimum performance for your peak HP. By using a Dellorto, you have a range of chokes available for any given carb model, ie, with a 40 Dellorto you can run a range of chokes from 25-32mm diameter. A 45 Dellorto's choke size range is 28-36mm.
4. These carbs are fitted with an accelerator pump and are relatively easy to tune.
5. Changing jets on these carbs is a breeze. No need to remove the carb from the bike.
6. Once tuned, they stay in tune with no need to do individual balancing, as the butterflies are fitted to a common shaft.
7. Velocity stacks are available that can be enclosed in a purpose built airbox.

The dis-advantages are:

1. Space would be tight around the rear of the frame because of the length of these carbs.
2. Economy is slightly compromised by the use of a pump jet circuit.

Just another option for you to consider.

[drhach]

Cfm

CFM is not hard to calculate. You need to do some conversion, but it's not that hard. What does CFM stand for? Cubic Feet per Minute. That's volume per minute. Well, your volume is the volume of the bike (750cc, 1000cc, etc), and your per minute is the RPM of the engine, right? Your volume is constant, in other words no matter how fast or slow you are going, the engine is the same size. What changes is the RPM's. So you you need to find you CFM at the max RPM of the bike. Call it 10000.

One cc is 1centimeter X 1 Centimeter X 1Centimeter. 1 centimeter is equal to .033 feet so 1 cubic centimemeter is equal to .033 feet X .033 feet X .033 feet. Or .0000359 cubic feet. Multiply that by the size of the bike. In my case 1000. So 1000 X .0000359 is .0359 cubic feet. Mulitply that by the maximum RPM (10000), .0359 cubic feet X 10000 RPM and you get 359 CFM.

Now there's one other thing to consider. These engines are four stroke engines (intake, comperssion, power, exhaust). That means that for two turn of the crank, they are only drawing air/fuel once. So, you take your previous figure and divide by two. So, theoretically, you need about 180 CFM for a GS1000 to function at 10000 RPM.

Hopefully I didn't bore too many people.

[lecroy]

"But the issue has been brought up about the CFM of a Harley vs the CFM of an inline 4, and consensus is that the inline 4 will pull a lot more CFM. Maybe start with a 38mm Mikuni and go from there?"

I'm just tossing out examples of things I have seen myself. Let's run the same numbers for my bike and we get in the 250CFM range. Add 12 PSIG of boost (where I stopped last year) and you get around 380 CFM at the compressors inlet. All with one little 42mm carb. At 30 PSIG it would be around 450CFM.

BTW, this carb is only recommended for applications in the 210 CFM range. I guess my point of this is that if your not looking for an optimum solution, you can get away with a lot.

Post pictures of your manifold once you get it done.

[Commodus]

CFM is not hard to calculate. You need to do some conversion, but it's not that hard. What does CFM stand for? Cubic Feet per Minute. That's volume per minute. Well, your volume is the volume of the bike (750cc, 1000cc, etc), and your per minute is the RPM of the engine, right? Your volume is constant, in other words no matter how fast or slow you are going, the engine is the same size. What changes is the RPM's. So you you need to find you CFM at the max RPM of the bike. Call it 10000.

One cc is 1centimeter X 1 Centimeter X 1Centimeter. 1 centimeter is equal to .033 feet so 1 cubic centimemeter is equal to .033 feet X .033 feet X .033 feet. Or .0000359 cubic feet. Multiply that by the size of the bike. In my case 1000. So 1000 X .0000359 is .0359 cubic feet. Mulitply that by the maximum RPM (10000), .0359 cubic feet X 10000 RPM and you get 359 CFM.

Now there's one other thing to consider. These engines are four stroke engines (intake, comperssion, power, exhaust). That means that for two turn of the crank, they are only drawing air/fuel once. So, you take your previous figure and divide by two. So, theoretically, you need about 180 CFM for a GS1000 to function at 10000 RPM.

Hopefully I didn't bore too many people.

Yay! I knew somebody would know! :-D

[Nerobro]

While that is "true" that's also assuming zero intake vacuum, and 100% VE.

Most carbs are rated at a certian number of inches of vacuum. While a 180cfm carb may be enough, you'll be looking at signifigant vacuum at 10,000rpm. Vacuum means less horsepower. So you'll want a carb that's much larger than that. dont' ask me for hard numbers, becuase I came up a blank when I last started trying to figure out what it would take to put a single carb on a GS.

Keep in mind, that in comparison to "real" engines, motorcycle engines are almost always disturbingly overcarburated. My little 49hp bike has a 4bbl carb with 1.25" venturis. Though the bike really only breathes through one carb at a time. So if you had a manifold on it.. in theroy a single carb would do it. Still it's a 1.25" carb. :-)