Where to start diagnosing power loss/startup problem
I have a 1978 Datsun 280z and am having some trouble figuring out where to start diagnosing its first engine issue. Got the car about a month ago and it started and drove just fine. A few days in I drove it a little hard and it suddenly started stuttering and hesitating around 2500 - 3000 RPMs. Took it home and it was idling at around 500 with a bit of white/grey smoke coming out of the exhaust. The level of exhaust smoke is increased when pressing the accelerator.
I thought maybe I had blow a head gasket, however, during the next week I did a chemical test which showed negative for exhaust fumes coming through the radiator. Let it sit for a bit longer (not a lot of time to tinker because of work), still running at around 500 with a small amount of smoke through the exhaust. I then did a compression test which showed 130 psi across all cylinders. Note that the spark plugs are black so I suspect it's running very rich.
That leads to this week when I was planning to do a wet compression test to rule out worn piston rings. Start engine and the idle is down to 250. Give car a bit of gas, and car stalls and refuses to start up again.
So now I'm stuck and wondering where to continue with diagnosing this problem. Maybe it's a busted fuel pump, or a major vacuum leak? Timing? I am planning on doing a leakdown test tomorrow to see if air is escaping somewhere and then checking the fuel pump but after that I'm a bit rudderless.
Any tips you guys have would be immensely appreciated!!