My 1981 Kawasaki car 650

I brought a 1981 Kawasaki car 650 off of Craigslist i pulled the carbs and they were missing some parts of the accelerator pump so I brought a set of mikuni 24ss carbs with out the accelerator pump they have 102.5 main jets in them and they have the pilot/ gas adjusting screws on the bottom/ outside nof the carbs i cleaned them i have the adjuster screws  set at about one. And three quarters out from lightly seated  the motorcycle has the stock air box/ filter on it and a 4 into 1; exhaust pipe on it and some moron drilled  four holes at the end of the exhaust they are about a dime size in diameter and  he drilled them around the original hole at the exit of the 4 into 1 exhaust pipe why I don't know anyways  I can get it running so so but it will only keep running with about a quarter of the choke on  even after it warms up which is very quick the pipes and engine get hot very quick and when I try and give it a bit of throttle it wants to die  so any advice would be appreciated I thought maybe I should go up to 105 or 107 5  main jets ? Also should I maybe get someone to weld the extra holes at the end of the 4  into 1 exhaust? Thanks members and fellow bikers 

Howdy. It sounds like you have the carburetors from a 78 model.  Carb tuning isn't my forte, but you may need to increase the main jets and maybe the pilot jets. The "choke" on VM24 carburetors is an enrichener, so you're cutting the fuel supply from the starting circuit when closed and that may be why it's dying. ???  

1978 KZ650-B2 carburetor parts >>  www.partzilla.com/catalog/kawasaki/motor...-b2/carburetor-parts

The first thing is to confirm which set of carbs you have.  The table in this thread should help you to figure that out.
www.kzrider.com/forum/3-carburetor/59903...sheets-for-kz-models

If you look through that table, you'll notice that the largest jet used with the KZ650 VM24 is 102.5, and many came with smaller main jets.  Assuming you are still using the stock airbox, I do not think it's going to be any help to increase the main jet size.  Drilling holes in the exhaust is not very likely to require a substantial change in jetting.  I don't think closing those holes will solve your problem.  But it may make the bike less noisy.

Also, the main jet circuit has almost no impact on the behavior of the carbs just off idle.  The main jet doesn't really start to come into play until you are at 25% throttle or above.

It sounds to me like your pilot system is clogged and needs to be cleaned. It could also be that the pilot screws need to be tuned to provide the correct idle mixture.

This thread has some photos from the factory service manual for the larger bikes. The factory service manual gives a lot of detailed information about how the carbs work and how to adjust them.  kzrider.com/forum/3-carburetor/614399-mi...re-screw-which-is-it

You should find the factory service manual for the year specific to the carburetors you have and use those instructions to adjust the pilot screws.  Many of the manuals can be found on this site in PDF form.

If that doesn't help, you'll need to do a deep cleaning of the carbs.  This usually involves completely disassembling every single part.