help with my carbs?

Joined: February 27th, 2018, 1:51 am

March 23rd, 2018, 11:33 pm #1

So the motor that goes in my frame is also a '78 cb750. I HATE messing with those old quad carbs on those 750s... And then I remembered a bike I used to own. Albeit it was a 550, someone had made up some big 4-1 intake manifold for it with copper pipe, and it had just one large carburetor. Could such a thing be attempted on my 750? Even just two 2-1 carbs would be better. Does anyone know how Id even begin to go about this? where I could find a large carb, what size the stock ones were? (32? 34?) and what size would be suitable for a 4-1 or a 2-1.
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Joined: February 23rd, 2018, 10:11 pm

March 24th, 2018, 12:04 am #2

I remember some kits with one or 2 carbs advertised in the magazines
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Joined: February 27th, 2018, 1:51 am

March 24th, 2018, 12:13 am #3

I know POSA had a 4-1 carb setup at one time. Super hard to find the manifold for now, but there were some pics over at hondachopper.com of a POSA clone that looked like some black Iron pipe welded up. Cycle X has a 4-2 kit with 2 34mm Mikuni carbs but $500 is a bit pricey for just a carb setup. Im pretty decent at fabrication. Id prefer a 4-1 but id settle for 4-2. There doesnt seem to be too much info on the topic
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Joined: March 2nd, 2018, 11:25 am

March 24th, 2018, 3:49 pm #4

Trust me those 4 carbs are pretty simple. All those other solutions are not going to make it easier. Go over to Honda Choppers or the SOHC websites. Plenty of great information. Get them CLEAN, be willing to do accurate plug chops and maybe take them off and on a few times to change things. Be sure to have good intake boots and soften them first.(wintergreen oil soak ) Get the right size worm clamps. It will cost you about $100 for good kits ( with needle jets and jet needles ). If you do go another route, don't just trash them. That's happened a lot in the past and makes them harder to find. There are guys on those sites that will rebuild them for you. You'll still have to do the finally tuning. Give them your air box or air filter selection and the type of exhaust and they can get you close.
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Joined: March 27th, 2018, 2:14 pm

March 28th, 2018, 3:47 am #5

+1 on keeping the 4-4 carbs. Sometimes just a cleaning and vacuum synch will do wonders if they've been neglected for a while. It's not hard to do, dial kits are pretty cheap and it does make a difference when it's set right. Id try that before you give up.

Honda kept the 1 to 1 carb setup even through the 6 cylinder goldwings, it's hard to beat it.
Keep at it
Lapeer MI, let's ride
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Joined: February 22nd, 2018, 9:01 pm

March 28th, 2018, 5:25 am #6

I used this pore boy manometer for years until I realized that I only owned one bike with lots of carbs and I needed some kindling. It's a length of clear tube with atf inside stapled to a scrap of one by, Takes a little longer to balance two at a time but way better than buying a seldom used expensive tool.
Dusty  
Poorboy Manometer 001.JPG
Driving that train, high on cocaine
Casey Jones you better, watch your speed
Trouble ahead, trouble behind
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Joined: March 27th, 2018, 2:14 pm

March 28th, 2018, 12:56 pm #7

Dusty-Dave wrote:I used this pore boy manometer for years until I realized that I only owned one bike with lots of carbs and I needed some kindling. It's a length of clear tube with atf inside stapled to a scrap of one by, Takes a little longer to balance two at a time but way better than buying a seldom used expensive tool.
Dusty  
Poorboy Manometer 001.JPG
I've had one of these for years and it's easy once you figure out the process. I adjust/check them as part of the spring tune ups.

Sent from my SM-G892A using Tapatalk

Lapeer MI, let's ride
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Joined: March 4th, 2018, 3:40 am

April 23rd, 2018, 12:40 am #8

heavymetalthunder wrote: So the motor that goes in my frame is also a '78 cb750. I HATE messing with those old quad carbs on those 750s... And then I remembered a bike I used to own. Albeit it was a 550, someone had made up some big 4-1 intake manifold for it with copper pipe, and it had just one large carburetor. Could such a thing be attempted on my 750? Even just two 2-1 carbs would be better. Does anyone know how Id even begin to go about this? where I could find a large carb, what size the stock ones were? (32? 34?) and what size would be suitable for a 4-1 or a 2-1.
I am getting ready to pull the carbs, again, from my 82 GPZ550.  Already ordered the DynaJet kit and rebuild kits for the four carbs.  It has only run once since I built it, (it was sitting for about 20 years) constant issues with the carbs and Petcock.  TK 26 carbs.  I thought about trying to do something different too, but, they worked great then, so...
We're gonna hit the road for one last time
We can walk right in and steal 'em blind
All that money
No more runnin'
I can't wait to see the old man's face
When I win the race
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Joined: April 30th, 2018, 12:32 pm

May 1st, 2018, 1:29 pm #9

Here is a 4-into-2 setup for the SOHC:

SOHC
(2) VM34 mm Mikuni carbs (prejetted)
Special cast alloy  manifolds.
Motion Pro turbo throttle (7/8 bars)
Motion Pro throttle cable.
Velocity stacks ( screen and foam type)
Carb rubbers and stainless clamps.
Instruction sheet, Extra jets
 http://www.cyclexchange.net/Honda%20Twi ... 20Page.htm                                                                                                      
$499.00
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Joined: March 4th, 2018, 3:40 am

May 10th, 2018, 4:29 pm #10

Damn!
We're gonna hit the road for one last time
We can walk right in and steal 'em blind
All that money
No more runnin'
I can't wait to see the old man's face
When I win the race
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