Effect of non return valve on engine running

Appreciate any comments....I am running the engine outside of the Dino after a top end rebuild...but find it's not running great ...shorting out the plugs on one side one at a time don't seem to make much difference...I then noted that I do not have the tube that goes to the brake servo non return valve connected to anything..(it's with the car being painted) ...it's just open and it's that side of the engine that seems to not be pulling its weight....

Could this be due to that non return open pipe. ???

Thanks...always learning

 

Great...thanks