Motor won't run at throttle

by Ray
(Lusby, MD)

I have a 1987 Glastron with a 2.5l GM inline 4 cylinder.
The motor is hard to start and once it does start it idles ok. When you try to give it more throttle the motor tries to shut down unless you feather the throttle or take it back to idle. Total tune up on motor and it seems to be getting fuel. Any suggestions?

Thanks