Motorcycle Repair: Carb Setup, vacuum petcock, gravity feed

Question
Good day,

I have a 1990 LT160 with an 85' LT125 engine.  According to the parts diagrams, the carb on the 125 motor should have a fuel pump on the side of the carb but the carb that came with this bike doesn't have the fuel pump.  The tank is up high on the backbone so wouldn't gravity feed be enough?  The bike does run intermittently and seems to be a fuel supply issue.  I believe I have set the carb to the factory specs, cleaned it and also the fuel petcock was cleaned as well.  Any ideas if this different carb setup would affect the bike?
Thanks.

Answer
Eric,

sounds like the carb has been replaced with
another model, possibly an aftermarket replacement.
The "fuel pump" you mentioned is a fuel primer,
used to pump fuel down to the carb and help
starting I imagine. Have you checked if the
float bowl has fuel in it?
Is the carb fitting well on the engine, are
there any places it could be leaking air?
Can you feel any suction if you hold
your hand over the carb air intake
when starting?
Will it run with the choke on/off?
The carb you have should work with gravity
feed, does fuel flow out the float drain?
If you have a vacuum petcock, it needs
vacuum to open.