NewZed

You are starting from waaaay behind. That's the coolant hose from the radiator outlet to the water pump inlet that you have your finger on in that picture. Nothing at all to do with fuel. No offense, but you need to be careful before you start messing real fuel lines. Fix the fuel fill hose problem first. It's essentially in the cabin with you so any leakage at all is raw fuel smell. Don't mess around in the engine bay until you spend some time studying. " I also found out that the lines from the fuel fill to the tank leak when slightly overfilled and I am correcting that now." Good luck.

Got curious. One of several - http://forums.hybridz.org/topic/112994-rb25-flywheel-to-l-series-question/

Here's normal sound and normal speed. Don't know who it is.

Mine sounded "cammy" when it was running rich. My neighbor thought it had a performance cam. It doesn't. Raise the idle speed, to at least spec., let it warm up and see what you think. You're off=spec. right now (low idle speed). so it's going to sound off. All engines sound about like that when the idle is too low. You've checked a lot of stuff, might as well change the idle speed to where it's supposed to be.

Idle speed is low. Not good for oil pressure or alternator charging. Beyond that you'll need to define what you mean by "off".

Same head casting number (design/style), and same head gasket?

Seems like there's a setting somewhere that isn't right. The ECU and software adjust timing by changing the coil grounding moment in relation to the base timing. So, the program just isn't controlling the coil ground like it should. The distributor is distributing and the CAS inside it must be communicating with the ECU to generate the base timing signal to create a spark. The engine runs. Could be that there's an input variable that is so far out of range that the software defaults to no advance. Maybe the MAP variable is set wrong. Maybe temperature reading? http://www.megamanual.com/ms2/ign_timing.htm Just offering ideas, and picking up some knowledge myself.

If the 78 AFM has the internal contacts for the fuel pump relay you can use it no problems. But the 76 AFM should work fine also. They're the same except some the 78's don't have the fuel pump control switch inside. You haven't mentioned fuel pressure or any of the basics that might cause a lean condition. Popping back through the intake is typical of lean.. That's why I mentioned the vacuum leaks. If the engines ran fine before, don't do anything dramatic. It's probably something simple. Might even be that the AFM isn't plugged in, it doesn't have to be to idle If it won't rev without popping, it certainly won't drive well. If you get lost, the best thing to do is download the EFI Guide and check things at the ECU connector. You can check that the AFM is properly attached, the coolant temperature sensor isn't shorted, the injectors are all connected,, etc. All from the Ecu plug.

You probably lost a lot of viewers with your title. Sounds like plug wires on in reverse rotation (easy to check), or off one hole (check timing? what is it?), or a vacuum leak. All intake air must pass through the AFM. Even the PCV system matters. The 78 should run perfectly with the 76 EFI parts. I have a 78 engine in my 76, and I've swapped ECU's, AFM's, ignition modules, and just about any other part you can think of, with no issues. I check my spare parts by using them. The 78 AFM even came with a fuel pump relay switch, just no wires in the harness for it (not your problem, just mentioning).

How much? A large number will generate more interest.

Another wild guess, or a clue for someone else - in Tunerstudio do you see the tach signal? Does it read the RPM? You said "tach" but I assume that means your in-car dash tach. I think that MS can use different sources for the tach signal. The software isn't perfected so it's highly likely that it's possible to set conflicting variables, that give results that don't make sense. Copied a paragraph from the manual as example. Maybe there's a way to set crank angle control, but still using coil output as trigger? Edit - and you're missing the crank angle signal. Only here for the puzzle. Anyone who knows the answer, feel free to crush my views.

Follow-up: Megasquirt is seeing your crank signal,and controlling the coil. The engine runs, but it's just not advancing timing. You're driving around with no timing advance at all.

I don't really have any ideas. Are you saying that no matter what the engine is doing the timing never changes. Revving the engine, watching the timing light at the damper pulley, nothing happens?

Have you been here - http://www.megamanual.com/ms2/tune.htm and looked at the section below? -

Add more detail. Like what's connected to the power transistor, MS settings, etc. Stuff that describes what you have, beyond "stock ignition system". I can say that there's not much to work with in your post, and I don't even have Megasquirt.

I'll see if I can figure it out but it's a tight fit and I don't have the urge to take things apart right now. In the meantime, you might just consider getting a typical Bosch relay with the diode already spec'ed and built in. They're very common. They even mold or print a diagram on the case, showing either a diode or a resistor or neither. I'm sure one of those would do the job and save you some time. http://www.bcae1.com/relays.htm

I'm going to guess it's just there for surge protection (flyback?) back through the AFM contacts when the start signal comes through. But I'm just guessing, no formal training. Here's a picture of the resistor inside the relay,1976 version (I had a broken one handy). I'll let you fconfirm the color code, I've forgotten what I never really memorized. The diagram is from the 1975 FSM Engine Fuel chapter. Edit - the internet makes things too easy... Digikey color codes. About 3 ohms, if my eye reads the colors right. Not much.

I don't think "megasquirt 2" is enough information. Lots of good stuff here - http://www.megamanual.com/v22manual/minj.htm

I assume it's been too wet to go do some real burnouts? It's an interesting setup, people will probably be interested in how it holds up. Did you say what you're using for the front mount? Not stock rubber and the belt?

It's not the block, it's the pistons inside. You can put negative numbers in to this calculator in the HG area, or just subtract from the stock gasket and put that in, to get an idea of what effect a shave has. Not exact once the shave gets in to the chamber's curves, but better than nothing. http://www.ozdat.com/ozdatonline/enginedesign/

39.7 mm, mating surface to mating surface. For whatever reason I have one sitting on the work bench right now. 280Z, but they're both S30.

Figure out what your tachometer uses to count and try to replicate it. 240Z's have the coil power running through the tach, they're called "current-triggered". 280Z's have a wire dead-headed from the coil negative post. They're called "voltage-triggered". Even when people get the principles right some times the adapters don't get it done. Put 8910 or 8920 in the search box - http://www.msdignition.com/instructiondownload.aspx

This is why we test the electrical components and their functions at the ECU connector. The 1980 EFI Manual is the best reference for that. Covers all EFI cars up to 1980. - http://www.xenonzcar.com/s130/other.php

Only one question was identifiable. Yes. Not much to it though, thin paper.

No dutchering is evident. Just some assembly required. This should help - http://atlanticz.ca/zclub/techtips/electrical.htm