Hey Jonfrabitoy, If you are not set on reinventing the wheel - there have been several nice sets of 1100 carbs on Ebay and there are plenty of motorcycle salvage yards that would probably be tickled to hook you up with some parts.
I am sure your project is possible but wouldn’t a single carb setup require that the fuel/air mixture make a lot more twists and turns before entering the combustion chamber ? The added length would sling the heavier fuel particles against the intake wall with every turn which typically requires a richer mixture to compensate for the loss in flow efficiency. Most designs then must add heat to the intake tube surfaces to try and smooth the air/fuel mixtures around the corners.
The only reason I mention some of the problems you may run in to when trying to install a single carb on a flat four cylinder engine is because I was involved in a similar project one time. A buddy spent a ton of money changing over from fuel injection to a single carb setup on one of the old air-cooled fast back VW’s that was a family free-be. The engine actually ran great but he decided it would be simpler to maintain if he ditched the FI. We first tired a intake/carb setup that stood straight up - but was too noisy inside the car. Because the rear interior had a flat panel directly over engine the aftermarket intake and carburetor had to lay on it’s side. With all the above mentioned fueling/ducting issues, that thing turned unbelievably temperamental and burned fuel like 12 cylinder Ferrari.
It is not that you probably can not design an intake/carb setup but Honda would more than likely have saved the production cost of those 4 carbs if it was feasible.
Good Luck, Michael
Of course, both your suggestions, carb distance from the valves and performance of the engine are very valid. The manufacturer (Honda) installs or positions the carbs, a design intent, 6 inches by linear measurement from the head port. The carbs meter the fuel another 2 inches back, to make the distance just to the head, 8 inches. The Goldwing engine is very forgiving, on other inline 4 cylinder bikes, the throat of the carbs are only 3 inches from the head port.
now, carbs respond faster when they are closer to the valve. the velocity of the air/fuel mixture is important as well, sometimes racers restrict or install smaller bore carbs to increase air/fuel velocity into the head port for better faster response. The goldwing is not balanced for racing, just cruising, so performance is important, but not paramount.
Next you mention air/fuel charge turbicity. Yes, there are more turns and a longer distance for the air/fuel mixture to travel before the head port. and this can be a concern for performance. will it cause the fuel mixture to richen??? Hum, I dont think that can happen.
If i install an orifice that can only allow a max flow rate through it, and nothing more, then it is fixed.
Heating? it might be desireable to atomize the fuel early, heating the manifold will cause the fuel to atomize or vaporize sooner, before it reaches the head port. it could help performance, good questions ??