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Discussion Starter #1
So I seen this posted today on craigslist near me and it got me to thinking about fuel economy. I wonder how this thing actually does and what if any thought went into where to place the card and if any thing was done to the inside to help with flow. Back in my day i used to alter and polish the insides of the intakes to improve flow. I also added divers in some making them dual plane which worked great on circle track cars.
 

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I think the rough edges help to disperse the fuel/air mixture better than smooth bore polished.


for the 4 cyl bikes, I doubt you can tell the difference while riding it.
True, intake ports should not be polished, don't know if it would matter on those long runners.
People just do those 1 carb conversions because they can't make the 4 carbs work right. Not much chance it would do anything better than the original setup when working properly.
 

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My single carb seem to run better than the original 4s.. I did the SCC for about $125 versus $1200 that was quoted to me for a 4 carb rebuild!
I sank too much money into those dinosaurs, for NO results.. They are just to finicky. If have the knowledge to get then running right, Great. I just got so sick and tired of dealing with those boat anchors. Just my thoughts. Im wasnt looking for fuel economy... I want this bike to run down the road, not a door stop!
 

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Sounds like my experience with carbs in general. I used to restore and run vintage Farmall tractors, and what finally made me sell everything off and go "modern" was futzing with the [email protected]# carburetors more than enjoying the tractors. Same with snowmobiles, I sold the two-smoke versions and went four-stroke and fuel injected. I just got tired of needles, floats, slides, and just generally smelling like gas more often than enjoying the equipment.
 

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Discussion Starter #7
Sounds like my days as well, either they work and work well or DONT, LOL! Me and my Kawasaki have a love hate relationship it loves to hate me, I usually end up re-synchronizing at least every other year. Have no problems out of the Goldwing though since I rebuilt them. I do use non-ethanol even though some say its a waste. Too me its cheap insurance for labor.
 

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If I could get the old carbs to work I would use them. (I still have them in a box) But, it seems like they would mysteriously break a slide, (how that happens, I dont know). Its not like I hammer on the throttle. Most Ebay sellers want $100 per, and they dont have the 755A's. I dont think they can be mixed with the 763's. (1976 and up) I like the single carb idea. (no syncing) Im still working out the kinks yet, but Im further along than the old 4s. All the posts seem to dead end just before the last hurdle. Info is somewhat scarce on the net. I mostly talk to the "OLD TIMERS" at work, but most havent touched a carburetor in decades. So the quest goes on.
 

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I have no problems making the Keihin work the way they were intended. Most people forget the valve must be adjusted before the carbs are sync'ed. On my 1100, the carbs get out of sync, I set the valves and the carbs are back in sync. It took a little work to understand how to bring back the carbs on my 450. They are basically the same carbs as the GL1000 which is one generation earlier than the GL1100. The GL1200 carbs are basically the same as the CB400/450 SOHC series. It is silly to sell a motorcycle just because you don't like carburetors.
 

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Original poster, that looks like a Hitachi two barrel, probably the smallest of progressive two barrels used on early Datsuns. Same design was used on many Subaru and Mazda but with larger venturi. The smallest version was a 20mm primary venturi with a 26mm secondary venturi. It should be stingy on fuel but have a decent punch when you crack the secondary. The small venturi should help keep the mixture moving faster through the setup. Like any conversion, some tweaking is likely necessary.

I am not a fan of the log-type manifold but there are lots out there. To me there are too many places where fuel could pool and cause a potential explosion. A few, quite a few, guys have made them from PVC pipe. Some have exploded. No one hurt, just extra laundry.

The ones using a VW type two barrel collector probably are safer as everything is sloped towards the intake runners and if the mixture is too rich, fuel wouldn’t have as much chance to pool enough for the above mentioned kerblam.

Another potential advantage would be ramming effect of the longer paths and an increase in bottom end torque. Would the average rider feel it?? I doubt it, but maybe.

I have two of those carburetors and a wild fantasy of using one on each side. Two years now and it all sits in a box in the garage.

Leaving the original Goldwing carb design out of the discussion, the single carb should see a steady flow through its venturi since the four cylinders take their turns pulling, 1 then 3 , then 2 and 4. The intake valve is open 235 degrees on early models, each intake opens 180 degrees apart, so at some points, the one carb is feeding two cylinders at the same time, but with a single carb the flow through the venturi stays in motion. Slight pauses in flow, but not as much as the stock setup whose venturi see a flow, and then an abrupt stop when the intake valve closes for 485 degrees crank rotation.

Using two carbs, like my fantasy, I will lose the advantage of continuous flow. 1&3 will pull, then a delay of over half a rotation (250 degrees) as 2-4 pull their charges in.

Another comment on the Hitachi carbs. The pic looks like a new knockoff. Cheap knockoffs are available new for just over $50 from China. I bought two. Pulling them apart I found numerous chunks of casting flash and drilling remnants. It would be worth the time to go through it to ensure there is nothing to plug stuff up when these pieces let loose.

There are a few versions available. I went with a standard cable choke but an electric choke is available. The early ones use a counterweight to assist second barrel opening up. I removed it to increase flow capability.

They would be fairly easy to rejet as the top comes off like Weber and others. Two are from the bottom, so proper placement so they can be accessed will aid dialing them in.
 
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