All very good suggestions. I recommend trying them all before doing what I had to do.
The problems stated above are typical from what I have read. However, it is also typical of Valk that has set for a long time without running. Floats stick, slow jets clog, bad gas from condensation in tank....I had the same problem after my bike sat for two months in a garage in cold weather. Full charge on battery and jumpers from my truck (truck ignition off)....would crank but not fire. Here's what I had to do to get mine running:
Fully charged battery
Drained all carbs
Drained fuel tank
Fresh gas with Seafoam
New spark plugs
Checked for strong spark at each cylinder (yes)
Checked for fuel flow from petcock (yes)
Checked for fuel in each carb bowl (not all). Right side cylinders firing but not left...kickstand side.
Still would crank but not run.
Removed carb bank an cleaned with carb cleaner. Focused on all moving parts and all jets
Pulled floats and checked for leaks (none)
Replaced all the gaskets....do this or else!
Used this video as a guide. It really helped me. Clymer's manual had you do extra steps definitely NOT needed. But, it's good to have for re-assembly diagrams.
https://www.youtube.com/watch?v=eDLTpQCTBscReassembled
Full choke (all the way down...not up)
Bumped starter and it fired up on the second try.... ran like a champ. But had fuel leak and vacuum leaks. My mistakes. Should have replaced fuel/air rail "O"rings and fittings and intake "O" rings while carbs were out. Pulled and replaced and runs great...until I hit that patch of sand. Recommend redeye's kits for all gaskets and "O"s...I'm sure there are other's.
Good luck. Hope it's just a weak battery. Either way, report back and let us know.