Hey Ebike, I responded to your other post about this too. I just used some heavy pliers to squish the top of the cap and pull up. It's fine to deform it, but definitely don't hammer on it!!
Now don't take any offense, but diesel AFR's are different than gas AFR's. This is super important. On a diesel, a richer AFR means hotter EGT's. A leaner AFR means cooler EGT's. I think your motor will be happiest and safest around 19-20AFR or leaner. You could run richer for short bursts. Definitely don't run 14.5 or you'll ruin your motor!!
Second thing, when you start tuning the spill control valve screw, turn in for more fuel and out for less. Do tiny bits at a time. DO NOT turn it in more than 3/4 turn total or the engine can go into run away. Rev the engine a bit with your hand on the throttle lever to make sure it does not hang or go into run away. If it does go into run away, just screw the spv screw back out until it stops.