The VT600 has two carbs. No VLX in 1995 in the states.
I would also check for exhaust leaks as a lean fuel mixture or a exhaust leak can cause a deaccleration back fire.
I see the you have a lean spark plug that is what is hard about a single carb with twin cylinders to make both cylinders run well with one fuel source.
Or you could have a air leak. you would need carb clean and spray it on the intake manifold area while the bike is running. If you get any substantial increase in RPM you will need to pin point the place the air is leaking for in the intake track and repair the leak. the common areas of failure are the in between the intake boot and cylinder head. the intake boot its self will crack.
also a weak cylinder can cause a lean condition as a worn cylinder needs more fuel to run correctly. this can be verified with a compression test.
this is what I see for a shadow 600
DO NOT KNOW WHAT IPC IS COULD YOU HELP ME UNDERSTAND?
carb specs are:
Float level: 7.0 mm (0.28 in)
Main jet: #115
Slow jet: #40
Pilot screw initial opening: 2.5 turns
Idle speed (+/- 100 rpm): 1200 rpm
try this link it should give you the info you want. If not let me know.
You are correct the VLX is a VT600CD that is its model code and it has a single carb.