http://vmoa.net/VMX12-Service-Manual01.pdf
https://www.vmaxforum.net/threads/new-vmax-owner-faqs-new-members-please-read.21240/
We have many threads about fixing long-term stored bikes,
use the search function.
A new powerful battery is probably #1 once you've solved the deferred maintenance items, like brake systems cleaning, carburetors adjusted after disassembly and cleaning; clutch hydraulics flushed, good tires, not 7+ year-old hard as a pair of petrified elephant's balls tires, a clean gas tank, replaced fuel filter, new or at least blown-out air filter, without mouse droppings, etc.
The carburetors need disassembly and cleaning, and the gas tank needs to be shiny metal inside, unless someone used a tank-lining product on it. Cleaning the carburetors without ensuring the gas tank is spotless is wasting your time.
Above, the carb enrichener pistons are way-out of adjustment. Be careful if they are frozen in-place! They can easily break, usually where the forked levers fit to the shaft, the narrowest part of the piston. You will need to separate the carbs into 4 separate ones to be able to replace the pistons, and they are expensive! About $60 USA, each.
Carbs for cleaning may only need to be separated into two pairs instead of being separated into four separate units. This saves you time and frustration in forgetting how they go back together, for the synch screws, being one area it's important to take LOTS of pictures and notes on the disassembly, so you can get them back together. READ the service manual, and be sure you understand the process before touching them! Did I say, take pictures and make notes?
Don't end up being this guy
If you have a hacked-up set of carbs, you could easily spend $500+ to replace parts. The CV diaphragms/slides are $158 each!
1985 Yamaha V MAX 1200 (VMX12N) Carburetor | Ron Ayers Part #10, diaphragms and slides are a single unit, though there are places you can buy aftermarket diaphragms, but they are tricky to replace, and the slides are easily broken.
Note there is overlap on the pics.
Rarely do I find the need to replace the needle valve seat (usually only an issue on high-mileage bikes), but the needle valve itself should be replaced (save the old ones for an emergency) if you tear-down the carburetors. OEM brass or I find the K&L kits are also good, as pictured. Unless someone hacked-up the brass, it can be re-used. Compare the #'s to the chart to see if you have proper ones for your bike.
Invest in a set of analog gauges for synchronization of the carburetors. They can be used on your GF's bike too. A couple uses, and they pay for themselves.
