Engine running rough, to put it nicely

[M5wanaB]

So I just got done transplanting a M42 into my '75 2002 and everything is hooked up but it is not running very well. It takes a good 7-10 rotations before firing up and it likes to back fire a lot. Once I get it going I can hold it at different RPM's and it sounds decent and will even Idle pretty decently. There is still the occasional backfire and when changing RPM or putting load on the engine the Backfiring gets worse and the engine is very low on power. Heres a little background on the car and engine.

1991 318is engine with 5 speed
Coil on plug conversion
M10 long tube header with M42 flange (thats the entire exhaust right now)
No oxygen sensor
I have the gray/black wire hooked together on the harness to activate the carbon monoxide potentiometer
K & N intake filter on the air flow meter
Throttle body heater and rats nest of hoses deleted

Let me know what you guys think may be causing this. I would just like to construct a list of potential causes and I will start going 1 by 1 and checking them off my list. Anything you guys think of I will check, thanks in advance.

for more info on the car check out
Project Schnitzer

[DesktopDave]

I'd suspect a fuel pump, FPR or one of the position sensors.  Check the temp sensors and the TPS too. Does the CO2 screw or door flap on the AFM need tuned?  I'm not sure if the USA M42 even has one.

[M5wanaB]

I'd suspect a fuel pump, FPR or one of the position sensors.  Check the temp sensors and the TPS too. Does the CO2 screw or door flap on the AFM need tuned?  I'm not sure if the USA M42 even has one.

Ill check the Fuel Pressure and to make sure I have the lines hooked up correctly, Also there is a screw on the AFM for adjustment but it is blocked off. I find it is usually better to just leave them alone, I do however have an extra AFM that has the block removed so the screw is visible. I was really leaning towords ignition or timing with this problem but sounds like it could also be fuel now huh? Guess I will just go through and check everything. What do you think about the Lack of O2 sensor? THat should just keep it in open loop right?

[doitover]

My car has an adjustable fuel pressure regulator that does not hold the rail pressure when off. It always take 6 or 8 turns before starting.

I'd test the AFM, mine had exactly those symptoms. I don't know that the AFM was bad but it turned out to be an AFM off a 6 cylinder car. The problem went away with the correct AFM installed.

I'd also check the fuel pump.