There is a good step by step guide here:

http://wiki.datsun1200.com/index.php/Engine_Troubleshooting_Overview

Sounds like ignition timing or valve clearances, but by working through it step by step you can gradually eliminate each possible cause till you find the one that is the problem.

I think ignition releated causes are the most common for car wont start, or car runs like a bag of #### issues...

Rofl it seams everyone has a different idea

ill chuck in my 2 cents

exact same thing happend to me recently under similar circumstances.

turned out to be my exhaust was blocked and had to replace the muffler as the motor couldnt flow and let the exhaust fumes out

perhaps try putting your hand over the exhaust pipe and have someone turn the engine over. If you cant feel any thing coming out the exhaust then its blocked and wont start or run (like the old banana in the exhaust pipe trick)

good luck

if when you pour fuel down carby it runs (but poorly), spark should be close enough to run. are you getting fuel out of the feed line between fuel pump and carb (maybe krook new pump - happened to me) or try blowing back into the tank from the feed side of the pump it may just be a blocked pickup in the tank. give it a try.

if you have fuel and you have spark, try adjusting the valves. more often than not, as the engine runs the valve clearance gets tighter, eventually causing the valves to actually stay partially open, this would explain the backfire and rough running.
because the engine is cold, set the adjustment at 0.012 in, until it is warmed up and then readjust them to 0.014 in. when hot.

Put a wire direct from the battery to the coil and see if it will run whilst "hotwired"

EDIT: you didn't say that it even tried to fire whilst cranking so this may achieve nothing.

Quote:

Thats what I was thinkin!

rings wouldn't just "GO" like that they slowly wear out over a long time

what about the rings? It may be them.

Sounds weird, 3 things make these things go, fuel, spark and compression.

All you have to do now is get them happening in the right order.

I have just put the A15 in my ute and I can highly recommend it! I have some contacts if you need them, PM me.

check around the jap wreckers, classifieds section here on the forum. as far as legal mumbo jumbo is concerned i am not sure, there is very little in ways of identifying an A15 from an A12 or A14 appart from the numbers stamped on the block which can be ground off in 2 minutes.
Here in WA we don't need RWC so I just put the A15 in and left it at that, as far as rego goes it still is an a12 heck I know 2 mates of mates with big hp SR20DET 1600's still regoed as L16's just need to live in somewhere remote enough to go unnoticed and to look at them they don't look like serious dattos, just dirty old brown things stock as a rock on the out side
sorry for rambling on I guess it's up to you whether you choose to have it engineered or not is what I am trying to say