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Here is the background...
A couple of years before I bought the 1000 I was thinking about doing something with an old wing. I thought sidedraft Weber's would look pretty cool so I came up with a manifold design. After a long time (a very long time) I decided that the tubes I designed were impossible to bend. I sent the design out for quote to a couple of rapid prototype companies. The cheapest quote was $3400 for the pair. That wasn't going to happen.
When looking around the internet I came across Randakk's Weber kit and went that way. The downdrafts are much more efficient than my sidedraft design. Suck, bang, blow.

But I haven't given up on the sidedraft idea.

Since I picked up a decent engine I started playing with the sidedraft design again but with stock carbs. Here is the concept. I'm trying to build composite manifolds. The tubes will be fiberglass and the manifold bases will be aluminum.
Since the plenum is the fuel source for the stock carbs I need to build aluminum blocks that will mount to the carb fronts to emulate the plenum. The air cutoff valve will go somewhere (I don't see any big hurdles with that). I expect the linkage to be a real joy but keeping the stock centerline distances of the carbs will allow the stock synchronizer gizmos (between the carbs) to work. I will have to come up with a synchronizer for the left-to-right adjusment.

Here is the concept (the right side is shown). Here is the jig for aligning the tubes. (I have the left jig mounted on the right side cuz I was too lazy to take the carbs off the engine.) The green foam things are the mandrels that I'll be wrapping in fiberglass. Once they are painted and glassed, I can pick out the foam and fill the glass tubes with paint stripper to get rid of the paint. That part works.

It will be fairly ridiculous. I have no idea if I'll be able to tune them.
It's gonna look cool. I'm showing velocity stacks but they'll need air filters to keep the rocks and rain out.


What you have to remember is...there is no spoon. - from The Matrix

What a fun idea!

Do you remember a post a couple years' back where one of our members stuck the carbs to the outside my just reversing the runners? It looked pretty cool. The carbs pointed out and forward. He said he put it on just for looks but went no further. I happened to see his bike on CL today. I think he had a Valk tank and a monoshock. I was down looking at my boat anchor project and it looked doable. Linkage would be fun, tuning probably more fun. It would leave a lot of room above the engine. Gas tank?

I just found the Valk tank post, gunny,..... it wasn't his post I am thinking of. I have a good memory......it's just really slllllowww. By next week I should remember it.

Remember what I told you about the air cutoff vlalve.

Love the concept!

gregforesi wrote:Since the plenum is the fuel source for the stock carbs . . .

Me confused, I think you mean AIR source? Fuel comes from the carb itself, downstream of the plenum, right? My confessed very limited understanding of CV carbs is that they like a stable isolated air source and is why the plenum or air box is highly beneficial and are difficult to tune with individual pod filters or air source. Not impossible, but very challenging. My 900F with CV carbs had individual K&N filters when I bought it, ran good, but a stock air box would out perform it and got better fuel mileage. Tuning was a real PITA. Eventually put Keihin CR Special direct mechanical lift carbs on. OH BOY! what a difference.

Not trying to throw a wet blanket on your party, just my experience.

I don't want to put words in Greg's mouth but I think what he means is the fuel is delivered to the carbs through the plenum.

gregs concept art shows a black block directly between the velocity stacks and the carb bodys
it has red hoses running into it.

I like this idea, would like to see where it goes. It would look pretty menacing from thr front!

I ran this idea past Robin a couple of weeks ago so he knows what direction I wanted to go. Rob agrees that tuning will probably be an issue. The DCOE Webers would be a piece of cake compared to the stock CV's since jetting is highly adjustable (and available). Re-jetting the stock Keihins may be an issue. As has been noted here numerous times, they are fussy on the intake side. On the other hand, I think I'll be able to prove or dis-prove the design using the stock carbs. A new pair of DCOE's are almost $800. Picking up used ones would be an option, but you never know what you're getting with used carbs. At this point and with an un-proven design, I thought keeping out-of-pocket expenses down was advisable.
Prior to picking up the 76 engine I had never been into the stock carbs (or even thought about them). My recent thread regarding "What am I looking at" was helpful in pointing out what the different holes are for in the front of the carb. As Fish points out, the blocks mounted to the carb fronts allow attachment points for the fuel lines to feed the small holes in the carb fronts. They will also keep the carbs aligned, allow attachment of the air filters, and provide filtered air to the vent holes in the front of the carbs, and (if I go that way) the air-cutoff valve.
Rob mentioned to me that the air-cutoff valve could be eliminated. After staring at it for a while, it's not difficult to incorporate so I'm thinking I'll keep it. I will just need to run an air line from right to left to couple all the carbs together to the valve. For both fuel and the air-cutoff valve, exterior plumbing will replace the internal functions of the plenum.
With the stock carbs I don't think this will be a "max power" design. I may have to limit the air intake to get the things to work without running way lean.
All this keeps my brain busy anyway.

Phenomadreamable ......

Gord

Could you use the the stock plenum and build new sections to mate each half?
That should restore the needed intake structure for the CV's.
You could use brake line pipe for the gas and air runners in the new halves and use stainless hoses to connect between the two sets of plenums.

Also, a question. The stock intake manifolds (between the carbs and heads) seem to get as hot as the head, and thus aid in evaporation of the gas from the carb. How can that be done with the fiberglass ones? Having a longer run, seems to make that point more important.

Interesting idea! I wonder what actual effect the longer intake runner will have?
I don't know what you have in mind for getting rid of the air cut valve but you may be interested to know that 1 of the carbs on my 75 has an extra brass jet under the diaphragm which in this case is just a blanking plug but is threaded the same as the pilot air jets in the elbow. I removed the plug and it enters the pilot air circuit in about the same place as the elbow based one. The extra brass blanking plug is situated on the opposite side to the primary and secondary air jets. On a normal carb there is a non drilled stepped hole there. The only way that it can get air is either round the slide or through the air bleed that comes up under the diaphragm from the plenum. Anyway the point is you could blank off the current pilot air inlets and drill and tap the blanked off hole thereby making sure you are getting filtered air to the pilot.

LikeMike - I was thinking about altering the plenums to almost flat. Then I would use them in place of the fabbed blocks. I don't want to tear up mine. Maybe Cyborg has something laying around. I have to think on that some more. The blocks as designed are 3/4" thick and allow for mounting other stuff (tight, but doable).

Quigon - an air-cutoff valve on each side would work so long as I can alter one of the left carbs to give it a vacuum takeoff. That would eliminate the cross-bike plumbing. I'm thinking on that too.

This idea has been vapor-ware for 5 years. I tried bending tubes full of sand, using a torch, cut pieces of tubing into pie shapes and welded them together, none of that was good. I have one tube almost complete. It looks pretty good. The aluminum manifold base plates should bond OK. they will have a large chamfer on the head side to accept a gob of resin. I'll look at a brace that goes back to the frame after I get the mock up on the engine.

As far as engine heat goes, at least the runners are all going downhill (they are equal length and 9" long). The Randakk manifolds stay cool on cool days until the bike has been running for quite a while. I don't think puddling will be a problem as such - but there might be a problem.

Ok, here is a dumb question. What would the impact be if the manifolds were not the same length? (Like one 3" and the other 9")