Sorry to not understand your reason for asking about a fabricator who made VW manifolds. If you had supplied more detail about what carburetor or carburetors you were planning to try, or that you just were hoping to find a fabricator familiar with Gen. 1's, I might have been able to offer some advice pertinent to your project. Regardless, here are some points of information, below.
Here are some links to threads on the site about different forms of carburetion, though they may not be for Gen. 1's. Perhaps you may find them of use in deciding what and how to proceed, if not, ignore them. They mostly involve replacing 4 carbs with one, unless you're at the Lycoming and Continental applications.
https://www.vmaxforum.net/threads/check-this-vmax-out.30231/#post-325358
Several 4cyl intake manifolds here, start at the thread's first post:
https://www.vmaxforum.net/threads/sohc-750-4-for-the-new-millenium.49457/#post-495204
Examples of 4 into 1's for downdraft carburetors on flat-four engines:
Sean Morley will be one person to whom you can speak to get information on alternatives to the four Mikunis we run, stock.
[email protected] He will tell you that you will probably end up with a big decrease in performance. It will likely decrease your bike's output by 20% or more. That would put our bikes in the high 80's HP.
I understand the frustration of having the fuel/induction system needing constant maintenance, and limiting your riding time to address the bike's need for work to be performed. Riding at a reduced level of that which the Gen. 1 is best-known for, straight-line acceleration, may be worthwhile if you're unable to get the motorcycle to reliably run until you switch to something simpler to operate and to maintain.
An observation, if the bike needs carburetor work every couple of months, instead of blaming it on the fuel, I'd be looking at the integrity of the fuel tank, and if it's rusted inside. One of my friends, who's been a Yamaha dealership mechanic since well-before the release of the Gen. 1 VMax, once told me, "if your tank is rusty, it's cheaper for you to buy a new tank than it is for me to pull the gas tank, clean the insides, coat it, and re-install it. " That was when you could buy a new gas tank for $150, they're a bit more now, $234.31 from Ron Ayres Yamaha. The last time I bought one, Yamaha was back-ordered, and I waited over 2 months to receive it. FYI.
Fuel Tank Comp
1FK-24110-11-33
Yamaha
Fuel Tank Comp
1FK-24110-11-33
Retail Price: $271.99
Your Price: $234.31
https://www.ronayers.com/oemparts/p/yamaha/1fk-24110-11-33/fuel-tank-comp
