Take the rocker cover off and check the intake pushrod is going up and down as this is what drives the pump.

Disconnect the pump from the "carb" and see if it pumps then if it does, then the blockage is in the carb, if it still doesn't then something isn't right with the pump. Bypass spring may be broken or pump valves may have crud in them

Very carefully pull the pump apart and check the valves don't have any bits of stuff in them. Take your time, don't break any gaskets or diaphrams and enjoy learning the mechanics of the engine.

My 170 has a funny characteristic where it feels like either an intake or exhaust valve (or both) doesn't completely close when turning it over by hand sometimes as you can't find the compression stroke. Valve clearances are correct, has one hour (8 flights) on the clock and runs like a swiss watch with 15%nitro 20%coolpower and 16x14 APC (in a sport airframe for running in) pulls 8k +- 50rpm on the ground and 2k tickover.