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Offline Jt550

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Riddle me this, riddle me that, a four into one carb could it do that!!
« on: March 24, 2011, 07:36:46 PM »
I've been BACK & FORTH with this....  ???

I got this bright idea to do 1 34mm Mikuni on a 71 CB500 ::)

My guru of a friend an bike tech & racer of almost 35 years swears up & down it will work......

Yet everyone I told doubts this.... Some say it won't start, some say it won't rev over 4K....

But FTW Who's right???

Im dying to know if it will work & have the "I TOLD YOU SO" moment when it does......  Or just punch & scream and cut the plenum in half & add a second carb..... But its 1 for now.....

What say you??? There's gotta be more then one of you out there has a background in this......... ;D ;D ;D
« Last Edit: March 24, 2011, 07:38:24 PM by Jt500 »
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Offline kslrr

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #1 on: March 24, 2011, 09:37:19 PM »
I figure that the fuel delivery passages will not be able to keep up with the demand.  Another reason for 4 carbs is that the path to the intake valves is as straight as possible.  And, 4 carbs vs. one carb on a manifold is more compact.
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Offline scottly

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #2 on: March 24, 2011, 10:05:44 PM »
Dyno-test your bike with 4 carbs, then again with the 1 carb log manifold, then decide for yourself if it "works".  ;)
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Offline Motoguy23

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #3 on: March 24, 2011, 10:21:49 PM »
I could see 2 carbs working much better. 

And now I hate you for putting ideas into my head.  ;D
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Offline scottly

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #4 on: March 24, 2011, 10:38:20 PM »
Thoroughly read "The Scientific Design of Exhaust and Intake Systems", by Philip H. Smith.
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Offline TwoTired

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #5 on: March 24, 2011, 10:45:11 PM »
It can work.  For some value of work.  Don't expect the high RPM of the original four carb set up, or the power.

4 - 22mm carb throats give 1520 MM squared  area.

1 - 34mm Carb will only have 908 mm Squared area.  So, breathing will be limited.

The log manifold will also have turbulence due to four inlet pulses disturbing upsetting smooth flow.  As pictured, I expect the outer cylinders to receive different mixtures than the center cylinders.
You may well get excellent fuel economy with the approach, though.  Just don't expect to go 98 MPH as the original did.

Cheers,
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Offline BLUE71TURBO

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #6 on: March 24, 2011, 11:03:04 PM »
 I would think the two outer cylinders would run leaner than the inner two cylinders because of the longer distance of fuel travel.   ???
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Offline turboguzzi

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #7 on: March 25, 2011, 12:00:01 AM »
will work, will limit performance compared to four separate runners, that's all. plenty of cars built like that.

limit by how much? hard to tell, but have a look at the airboxes that students develop for the CBR600 powered cars in Formula SAE. they are limited to one point of entry too.

 
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Offline Jt550

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #8 on: March 25, 2011, 02:36:36 AM »
Quote from: Motoguy23 on March 24, 2011, 10:21:49 PM
I could see 2 carbs working much better. 

And now I hate you for putting ideas into my head.  ;D

Sorry man, had to do it... I've had a Triumph 650 for the last 8yrs & it only had the one carb.... So it got me thinking, plus the 70's 750 chops with 1 side draft carb always blu my mind....
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Offline Jt550

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #9 on: March 25, 2011, 02:40:21 AM »
Quote from: TwoTired on March 24, 2011, 10:45:11 PM
It can work.  For some value of work.  Don't expect the high RPM of the original four carb set up, or the power.

4 - 22mm carb throats give 1520 MM squared  area.

1 - 34mm Carb will only have 908 mm Squared area.  So, breathing will be limited.

The log manifold will also have turbulence due to four inlet pulses disturbing upsetting smooth flow.  As pictured, I expect the outer cylinders to receive different mixtures than the center cylinders.
You may well get excellent fuel economy with the approach, though.  Just don't expect to go 98 MPH as the original did.

Cheers,

Am I allowed to say "I love you" ........ This is the type of statement Ive been looking for!!

But NOW I have to REALLY think if I wanna go the 1 carb route....cause SLOW is not always very fun......
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Tyler Durden: You're not your job. You're not how much money you have in the bank. You're not the car you drive. You're not the contents of your wallet. You're not your f*<king khakis. You're the all-singing, all-dancing crap of the world.

-78 CB550k with a BIG #$%* Eating Grin-

Offline Sam Green Racing

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #10 on: March 25, 2011, 03:15:18 AM »
Quote from: BLUE71TURBO on March 24, 2011, 11:03:04 PM
I would think the two outer cylinders would run leaner than the inner two cylinders because of the longer distance of fuel travel.   ???

Jon, does your average V8 have 8 carbs ::)

Riddler, watch out, Bat Man is behind you and he is moving your post to sohc4/bikes.
This forum is about performance related subjects, not how can I de-tune my bike by fitting just one carb.

Sam. :D :D :D sorry. ;)
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Offline Jt550

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #11 on: March 25, 2011, 03:24:18 AM »
Quote from: SamCB750A on March 25, 2011, 03:15:18 AM
Quote from: BLUE71TURBO on March 24, 2011, 11:03:04 PM
I would think the two outer cylinders would run leaner than the inner two cylinders because of the longer distance of fuel travel.   ???

Jon, does your average V8 have 8 carbs ::)

Riddler, watch out, Bat Man is behind you and he is moving your post to sohc4/bikes.
This forum is about performance related subjects, not how can I de-tune my bike by fitting just one carb.

It's all good man,,, sorry I put it in two places.. Had one to many shots... Never drink & post... ;)

Sam. :D :D :D sorry. ;)
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Tyler Durden: You're not your job. You're not how much money you have in the bank. You're not the car you drive. You're not the contents of your wallet. You're not your f*<king khakis. You're the all-singing, all-dancing crap of the world.

-78 CB550k with a BIG #$%* Eating Grin-

Offline cobrajunkie

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #12 on: March 25, 2011, 03:35:12 AM »
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Offline Jt550

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #13 on: March 25, 2011, 04:44:59 AM »
Quote from: cobrajunkie on March 25, 2011, 03:35:12 AM

THANK YOU Cjunkie!!!

One carb 750? Hondamadic??? HELL YES... What type of carb and size was that? An hav you had it on the street yet. I'm dying to see that thing blast off! Yet you might need a pillow suck in your boxers for the pot holes... ?is that seat wood!?

Either way BIG Thanks!!!
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Tyler Durden: You're not your job. You're not how much money you have in the bank. You're not the car you drive. You're not the contents of your wallet. You're not your f*<king khakis. You're the all-singing, all-dancing crap of the world.

-78 CB550k with a BIG #$%* Eating Grin-

Offline tomsweb1

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #14 on: March 25, 2011, 05:00:38 AM »
....Dude, did you listen to the video... That poor girl, she doesn't deserve that! I'd be surprised if it took less than two minutes to get up to 60, if it did at all.

Think about it this way, Honda didn't put the extra cost of having three more carbs on the bike for fun. It is by far the best set-up for power and economy.

 It's going to be a lot of work to do this, and in the end you will get destroyed by bikes half your size. IMO, not worth the headaches or the cost.
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Offline Terry in Australia

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #15 on: March 25, 2011, 05:17:59 AM »
Ha ha, it's fun getting old, (well, I'll probably die before you, so it's not all fun) because on a good day you can remember what was going on back in the day, and back then, having 1 carb per cylinder was a revelation, it was mechanical art at it's best, and everyone who had a crappy old Brit or American bike with only one carb were jealous.

There were single carb kits around that used a mechanical injector that was supposed to be just as fast or faster than the stock set up, but I believe that the speed was measured as the bike was pushed off a cliff by a disgruntled consumer................  ;D 
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Offline wildcatmahone

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #16 on: March 25, 2011, 06:34:22 AM »
You got about 20 yrs on me Terry but it always suprises me when guys get a "big idea". Yeh one 34mm carb will work but not very well. It was an upgrade on some British twins to ADD a carb but not remove 3 from a 4 cyl.
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Offline fasturd

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #17 on: March 25, 2011, 07:13:28 AM »
And those choppers you saw with one weber were v twins... Most vintage CB chopper have two webers one on each side. 'cause its faster!

Anyway the Gold wing guys have been going back and forth over this for years as there are a few single carb conversions out there for guys who are too chicken to rebuild a gl carb set. They all have worse milage and worse performance. Like stated before if honda could have found a performance gain by going to one carb they would have.

Now all that being said I have seen some wierd single and 2 carb setups that "look" cool but I hate riding bikes that don't "work" cool and poor carburation is a pet peve of mine.
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Offline cobrajunkie

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #18 on: March 25, 2011, 08:20:28 AM »
Quote from: Jt500 on March 25, 2011, 04:44:59 AM
Quote from: cobrajunkie on March 25, 2011, 03:35:12 AM

THANK YOU Cjunkie!!!

One carb 750? Hondamadic??? HELL YES... What type of carb and size was that? An hav you had it on the street yet. I'm dying to see that thing blast off! Yet you might need a pillow suck in your boxers for the pot holes... ?is that seat wood!?

Either way BIG Thanks!!!


Not my ride.  I couldn't imagine splinters in my arse and my johnson being sucked into my intake. :o  There I go bragging again.
« Last Edit: March 25, 2011, 08:22:37 AM by cobrajunkie »
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Offline BLUE71TURBO

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #19 on: March 25, 2011, 08:43:11 AM »
Quote from: SamCB750A on March 25, 2011, 03:15:18 AM
Quote from: BLUE71TURBO on March 24, 2011, 11:03:04 PM
I would think the two outer cylinders would run leaner than the inner two cylinders because of the longer distance of fuel travel.   ???

Jon, does your average V8 have 8 carbs ::)

Riddler, watch out, Bat Man is behind you and he is moving your post to sohc4/bikes.
This forum is about performance related subjects, not how can I de-tune my bike by fitting just one carb.

Sam. :D :D :D sorry. ;)

               The car engines are water cooled. I would think that an air cooled engine would suffer way more in the performance department.    P.S.  How many post's do we need on the same subject ?
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Offline BLUE71TURBO

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #20 on: March 25, 2011, 08:46:26 AM »
Quote from: Terry in Australia on March 25, 2011, 05:17:59 AM
Ha ha, it's fun getting old, (well, I'll probably die before you, so it's not all fun) because on a good day you can remember what was going on back in the day, and back then, having 1 carb per cylinder was a revelation, it was mechanical art at it's best, and everyone who had a crappy old Brit or American bike with only one carb were jealous.

There were single carb kits around that used a mechanical injector that was supposed to be just as fast or faster than the stock set up, but I believe that the speed was measured as the bike was pushed off a cliff by a disgruntled consumer................  ;D 

                  :D :D :D :D :D :D :D :D :D :D  ;D
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Offline Jt550

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #21 on: March 26, 2011, 04:45:06 PM »
Quote from: wildcatmahone on March 25, 2011, 06:34:22 AM
You got about 20 yrs on me Terry but it always suprises me when guys get a "big idea". Yeh one 34mm carb will work but not very well. It was an upgrade on some British twins to ADD a carb but not remove 3 from a 4 cyl.

HEY Wild,,,,,
It wasn't a BIG idea,,,, so no need to be snarky..... >:(
Ive got 18yrs in the saddle & 5 sickels in my past... First one BEING a 78 CB550 "which I wish I never sold!!"

Ive just played with more TWINS, be it Brit or HD....

But I was noticing that its getting harder to get the whole bank of 4 for a good price,,,, An I might NOT go 34mm, it was just a # I put out there to get some of ya'll thinking.... It looks like 38mm is a better size...

Its easier for me to weld up a manifold & put the one carb on it... Its alot less BS for me to deal with... An to the "purists" Sorry guys this is the way Im going to do it.....

If you dont like it you can "stick It"... An if Im taking this all the wrong way, its the PBR talking.....
Cheers.... ;D
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Tyler Durden: You're not your job. You're not how much money you have in the bank. You're not the car you drive. You're not the contents of your wallet. You're not your f*<king khakis. You're the all-singing, all-dancing crap of the world.

-78 CB550k with a BIG #$%* Eating Grin-

Offline Terry in Australia

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #22 on: March 26, 2011, 05:19:29 PM »
Ha ha, yep, I think you better stay off the PBR mate, I don't think anyone's intentionally being "Snarky", just pointing out the obvious, our bikes seem to run best with one carb per cylinder.

No harm in you experimenting with one big carb though mate, and hopefully you'll post some pics or a youtube clip of it running, and if the mod meets or exceeds your expectations, a dyno sheet to shut down the "knockers". Cheers, Terry. ;D 
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So I said, "Hey mate, you haven't got any bike boots you don't need, do you?"

"Crazy is a very misunderstood term, it's a fine line that some of us can lean over and still keep our balance" (thanks RB550Four)

Offline Flying J

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #23 on: March 26, 2011, 05:35:50 PM »
I like the "big idea". I think 1 carb on a 750 would look funny just because the intakes would not be the same length. I do like the 2-4 carb set up that cycle x has. not sure how that does for performance but if Twotireds numbers are right you could get more surface area that way.
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Offline BeSeeingYou

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Re: Riddle me this, riddle me that, a four into one carb could it do that!!
« Reply #24 on: March 26, 2011, 05:49:41 PM »
Quote from: cobrajunkie on March 25, 2011, 03:35:12 AM

Haven't seen anything as dumb as that in a while.  Can't wait for the first time it backfires. ;D

I don't get the logic on your idea Jt500.  You state that it costs too much for a decent set of carbs so you want to fab up a manifold, buy a single carb and then have to screw around to get it to run most likely worse than the 4 carb set up. How much time and money will be tied up in that?  Now if you just like to experiment knock yourself out but to do it save money and hassle..... ???
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