Racer X

If it is not functioning as it should then that is a possibility. I wonder if the springs that hold the check balls get rusted and fail? I doubt they are serviceable, but the function should be easy to check.

I agree on the second point that cooling fuel will contract, and a vacuum will result. When the engine is not running, the vapor line can pull air in from the air cleaner side of the flow guide valve. I also agree on the first point, that as fuel is removed to feed the engine, and the PCV (and the vapor recovery) system is pulling fuel vapors from the tank, a provision to replace the volume must be in place, and as you point out the gas cap has a one way check valve to allow volume compensation. ^^^^ Yes. I agree that after 45 to 50 years the seats for the check valves may not seal as they did new, but by design they are meant to be one way only. So the flow passes through the air cleaner inlet, past the first check ball, then joins with the fuel tank inlet, past the second check ball and is drawn into the pipe at the crankcase vent, which gets drawn into the engine as I described earlier. When the car is parked, vapors in the fuel tank are contained in the tank headspace, and the surge tank (provided the check ball in the flow guide valve is still seating properly).

How can the fuel tank create a vacuum?

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Also keep in mind that the flow is not constant during engine operation, as the vacuum changes as engine operating conditions change. At idle there is sufficient vacuum to pull the vapors into the engine. During acceleration vacuum drops, at wide open throttle it is at zero, and during deceleration it will be at the maximum.

Correct. And at the flow guide valve, it joins the fuel vapors from the tank, and is drawn to the large pipe at the crankcase vent, then drawn to the PCV valve and ingested by the engine. Notice in the picture you posted the arrow at the flow guide valve, showing the flow towards that pipe (I can't see that as your picture cuts it off, but pretty sure that is where the flow goes).

So the large line from the crankcase goes to the balance tube, where the PCV valve is. During engine operation the crankcase vapors are drawn into the engine through that connection with engine vacuum. The fuel tank vapor, and any residual aromatic hydrocarbons lingering in the airbox from any fuel slosh from the carburetor throats, vapors from the cam cover hose, all get sucked along and ingested with the incoming air fuel mixture.

Dogs love trucks.

Looking good. I wish these engines had a cam chain, rather than a belt. Broken cam belts are so messy.

Thanks for sharing this innovative approach to frugal classic car ownership. Looks like an awesome job, with the skill of a cosmetic surgeon. Oh, and a bamboo workbench. Nice.

Helicopter tape. Produced on military contracts to a government specification. Very much like Gorilla brand tape. The stuff is like duct tape on steroids. Extra sticky, extra durable. You should have a suitable tape there.

Looks like it is for the emissions equipped L series 6 cylinder engines. The threaded holes are for the AIR system. Any pictures if the ports, and then flange thickness?

Looks like the 100,000 BAT auction Z is stalled at $104,000 with a few hours to go.

If your injectors were blocked, it would't run, or it would run very poorly. Pressing on the throttle in of itself doesn't directly cause more fuel to be injected. That's why I mentioned earlier about not touching the accelerator pedal when cranking the engine to start it. The system is designed to start without accelerator input, and will automatically provide the correct amount of air and fuel for startup, and provide a slightly higher idle with an enriched mixture for cold starting. The control module looks at many parameters. engine speed and load, coolant temperature, ignition, then processes the information and sends a signal to the injectors causing them to pulse at a given frequency. The higher the frequency, the more fuel is injected. I admit I didn't read through the entire thread, but in the recent posts your description of symptoms indicates inadequate air getting into the engine at idle. I've already commented on solutions there. Now you mention it won't rev up. That might indicate a fuel pump that is failing, and cannot keep up with the fuel system demands. You mentioned that there was a problem with fuel pressure, and that you corrected that. Have you done a flow test?

As mentioned, I have limited experience with the system on the Z, but quite a bit with domestic, and some other import brands. You commented about the crankcase vent allowing the carbon buildup behind the throttle plate. This is common, I've "fixed" lots of cars for poeple by simply removing the throttle body, cleaning the carbon, and reassembling. Cost? My time and some carburetor cleaner. So it might be something to look at, and insure the idle air bypass is clear too. Regarding the timing. I would set the engine to number one TDC (the positive stop method is perfect), then ensure the timing mark is at zero. If not, correct it, then set the static timing, start the car and set the timing after warming the engine and attaining a stable idle. Also, while looking at the initial timing, have a good look at the damper rubber. When it fails, bits begin to come out. If there is any doubt, replace it.

Sorry, I'm not knowledgeable enough about this particular EFI, but usually the throttle butterfly remains closed at idle (including starting unless one depresses the accelerator slightly while cranking to start, which shouldn't be done with EFI systems), so some provision must be in place to allow sufficient air to enter the engine for starting. The GM throttle body fuel injection systems used in the early days of electronic fuel injection well into the 1990's all used an idle air bypass to provide startup and idle air for engine air/fuel management.

Don't these have an idle air bypass circuit?

Funk it up.

Sweet. I have permanent YOM registration on my 72, and will be doing the same for the other Zs I am keeping, as well as my 72 Camaro.