Carbs
I have seen some of this before. What I did is :
1. Run the gas line directly to the carbs, no vacuum pump, no petcock. See if this runs okay.
You don't want to leave it like this, the idea of the two vacuums is to keep gas from running into cylinder and flooding crankcase when sitting for long periods of time if float bowls don't do their job.
It dosen't need these to work while running. If it doesn't run right, the carbs are a problem.
2. Then try reconnecting each vacuum , one at a time, and running to see if either causes the problem. I had to do all of this once, simply because I ran the tank dry and it sucked air into everywhere, when I reconnected everything again, all was okay.
I have some of these spares if you find them faulty.
I have a 96 monster 900. I changed some fuel lines and now i can't get the gas to flow to the carbs. I checked the vacuum lines that come off the intake manifolds and they have pressure. so far i replaced the fuel filter and spark plugs and swapped in a new battery. even sucked on the line that goes to the carbs still no gas. before i get a rebuild kit for the pump is there anything else i can try. Now just so i have this right the top vacuum line goes to the carb. and the bottom line is the fuel supply. Please let me know if this is correct. the pump does not have arrows.