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Discussion Starter · #1 · (Edited)
Disclaimer: This is not intended to start a discussion on the use of JB Weld, unheated manifolds, etc. It's just what worked for me.

Weary of battling 30 year old carbs on my 83 GL1100A, I built my own single carb setup using aluminum tubing and JB Weld. I figured if PVC, old cutting boards and RTV worked for someone for 10 years, I'd be OK.

There are enough free pix on the net of these manifolds to take the mystery out of the design.

1 3/4" and 2" aluminum tubing from speedymetals.com ($45), a carb flange ($9), air cleaner ($15) and a 34 pict3 carb ($125) from ebay, JB Weld ($20), a bench grinder ($0), a rat tail file (0$), scrap wood for a setup table (0$) and away we go.

The major tools required were: a drill ($0), 1 3/4" hole saw ($5), a 2" hole saw ($5) and a sawsall ($0).

I knocked 2" holes thru the 1 3/4" tubing (you have to work from both sides) to make the tubing mate up to the 2" manifold, 1 hole thru gets you 2 runner "ends", I cut 1 3/4" holes into the 2" tubing for the 4 runners and the main intake. Cap the ends and make a throttle cable holder.

Pretty simple. I used "regular" JB 2 part and JB Steel putty over the top of those joints to pretty it up some although I was more interested in function than eye appeal.

Waiting for the JB Weld to dry up while the carb came from California, I installed a pair of CBR900RR coils that I had.

The result is a bike that started right up, a carb that took 3 minutes to dial in and great throttle response thru the entire RPM range, cold or hot. No jetting changes at all and the plugs are a nice tan after 100 miles of riding.

I'm in Daytona Beach, FL so it's usually warm here and I'm right at sea level or so.

By far the best $225 I have spent in rebuilding this bike.
 

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2000 GL1500SE
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That is a nice setup Bob. Hope it keeps working well for you. Hard to beat the price too.
 

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Interesting and nice to see a different approach.
Can you get some video and put it up?
 

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hey, a thought, I know pulling off the manifold is low on the list
but- I did some oddball homemade exhaust work and the vibration recracked what I'd done.
I pulled it, took it to a welding shop and 25 bucks later they did a GREAT job..made what I did look intentional and professional. 25 bucks....dang, wish I'd thought it was that cheap to start with...I expected a quote of over a hundred bucks. Guy looked at, looked back at the shop and said 25 bucks. wait here!

I like your thinking! cool job
 

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Vintage Rider
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I love it, though I would have actually welded it together.

I keep looking at the fuel injection setup on my LTD, and wondering if it could be turned into a manifold. Just remove the injectors and throttle slides, plug the holes, use the existing cast aluminum plenum and runners, and make a carb mounting base to replace the plastic cover where the air filter goes. Only problem I see is the carb plus an air cleaner would stick up to high. Could just cut a hole in the fake tank for it. Would be interesting having an air cleaner sticking up through the tank. Just a thought. I really do like the idea of a single carb.
 

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I like this type of setup and thinking to do the same to my 84 GL1200-A. But I second the question that esturdivant made about gas consumption with this new carb. I am wondering if does better on millage and or any other benefit to it. I seen a few people that install this setup and then I see it in Craigslist for sale, but they still state that the bike ran well with it. Any comments on this?
 

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Village Whack Job...
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I love how some people keep saying that single carb systems don't work, and how some people say unheated single carb systems don't work.

But every few months to year I see another home built single carb manifold that gets an otherwise crippled GoldWing back on the road for a fraction of the cost of rebuilding the OEM four carb system.
 

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There's really no reason why they wouldn't work . For years car makers made 4,6 and 8 cyl cars with one or two barrel carbs, so the principle has been proven. When a 4 carb'd wing is running, each carb supplies each cylinder with the proper amount of fuel. So as long as the single carb on a manifold is not jetted to big, the mileage shouldn't suffer.The manifold holds the fuel charge for each cylinder. Every time a cylinder inhales a charge of fuel, air is drawn in with a new fuel charge to take it's place. so unless there's a leak, the air/ fuel mixture should be balanced. Heat coming off the motor, and heat being given off by the radiator I would think would keep icing under control. And if it was a problem, insulation of some type I'm sure would cure it.My 2 cents.,,
 

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It's been demonstrated that single carb systems work. However, from my experience with the design of hydraulic manifold systems -- involving hydrocyclones and solids -- I doubt they they can be as efficient as multiple individual systems. It's very difficult to get even distribution of media to multiple outlets in a manifold, and an inline manifold is always less efficient than a circular manifold.

This principle may be less important for dispersion of liquids in a gas (as in a carb) than for solids in a liquid (as in a slurry) because the specific gravities of the two components are closer, but I can say that a single carb in and of itself will not contribute to efficiency.
 

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Discussion Starter · #16 ·
...But every few months to year I see another home built single carb manifold that gets an otherwise crippled GoldWing back on the road for a fraction of the cost of rebuilding the OEM four carb system.
You said it BW, that's exactly what I was going for. I am not overly concerned with fuel economy.
 

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It's been demonstrated that single carb systems work. However, from my experience with the design of hydraulic manifold systems -- involving hydrocyclones and solids -- I doubt they they can be as efficient as multiple individual systems. It's very difficult to get even distribution of media to multiple outlets in a manifold, and an inline manifold is always less efficient than a circular manifold.

This principle may be less important for dispersion of liquids in a gas (as in a carb) than for solids in a liquid (as in a slurry) because the specific gravities of the two components are closer, but I can say that a single carb in and of itself will not contribute to efficiency.
Come on Pete - what are you talking about man? ...

How 'bout this - YOU build us a conversion with a manifold of your design, get the right carb on it, put some time in on it, then post some results with pictures and video.

"less efficient" - than what? ...a professionally rebuilt rack @ $6-800.00 or a rack that has been gone through by its Owner a few times and still isn't right after $2-400.00?

Broke was right. Proven over and over again. It does work, and it can be made to work more efficiently than you realize.

:waving:
All subjective.
 

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Come on Pete - what are you talking about man? ...

How 'bout this - YOU build us a conversion with a manifold of your design, get the right carb on it, put some time in on it, then post some results with pictures and video.

"less efficient" - than what? ...a professionally rebuilt rack @ $6-800.00 or a rack that has been gone through by its Owner a few times and still isn't right after $2-400.00?

Broke was right. Proven over and over again. It does work, and it can be made to work more efficiently than you realize.

:waving:
All subjective.
Well, Cap'n, you sound as if I've offended you. Sorry if I did. Didn't mean to step on anyone's toes. As I said in the first sentence of my post: It's been proven that they work.

Secondly -- to answer your question -- "less efficient" (mileage-wise) than a multiple carb system designed for the bike. How much less efficient, I wouldn't begin to guess -- maybe not enough to make much difference. And I am well aware that the maintenance aspect makes the single carb system attractive -- the whole point, really in my opinion.

My post was intended to point out the reason why anyone making the conversion shouldn't expect better mileage than they would get with a properly maintained OEM rack. There may be other compelling reasons for making the change.

So please put the pin back in the grenade.:)
 

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Well, Cap'n, you sound as if I've offended you. Sorry if I did. Didn't mean to step on anyone's toes. As I said in the first sentence of my post: It's been proven that they work.

Secondly -- to answer your question -- "less efficient" (mileage-wise) than a multiple carb system designed for the bike. How much less efficient, I wouldn't begin to guess -- maybe not enough to make much difference. And I am well aware that the maintenance aspect makes the single carb system attractive -- the whole point, really in my opinion.

My post was intended to point out the reason why anyone making the conversion shouldn't expect better mileage than they would get with a properly maintained OEM rack. There may be other compelling reasons for making the change.

So please put the pin back in the grenade.:)
Hahha - Not offended. I think you've some conclusions based, in part, in theory and some in written Internet history.
I've a carb system designed for my bike. Designed by myself. I get better fuel mpg than the factory Keihins can provide. I also have more available fuel on-demand that is not dependant on vacuum for its delivery. I also have tuned intake tracts that take advantage of the moving mass within the runners. As a result, I've better throttle response from mid-range upwards than a factory set of Keihins. Admittenly, off-idle is a bit slower than factory but your average rider would not know it. I've a lot of mass to move with the vacuum I have, which is less than a stock engine would provide at idle.
I need no choke to start the bike.
I can fully control fuel delivery. Stock Keihins do not allow for half of the fuel control that I have with a Weber 2-barrel.
Stock intake tracts are heated. So are mine, as is my plenum chamber. Honda provides for heated intake tracts aft of the carburetors (the elbows) so why buck the system? Honda does it and does it for very good reason, others do it, others have done it, ...I'm doing it too. Others may not. Right-On.

Most that are making their way through their own conversion will hopefully know what a good stock set of Keihins are like so that there is something to baseline their effort from. Just getting it to run a lot better than what it did with the factory rack on is good enough for most in reality.
Again, things can get pretty subjective when optimism turns to enthusiasm.
Single carb conversions are becoming the new absurdity for the intellectual.
 

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That's interesting. I knew there were reasons for making the change, but didn't realize how long the list is.

Just out of curiosity, what kind of mileage do you get? With my recently-rebuilt stock rack I've been getting about 39-40 mpg, which is up from about 33-34. There are a lot of 50 mph (3000 rpm) miles in that figure, so that may make the mileage figure look better than it might be with a lot of highway miles, i.e. higher rpm miles. But I'm pleased with the results of the re-build so far.
 
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