Loss of power after 15 minutes

[nuteman]

Hi All,

I know about the vapor lock problem my 1973 240Z is prone to, but should I be losing power (and sometimes stalling) after only 15 minutes of driving in 65 degree weather? When I experience the power loss my temperature guage is well below max (about halfway of the range of the arc). I only have the mechanical fuel pump which is relatively new. I also have a brand new fuel filter. The car will accelerate well and drive great for the first 12 to 15 minutes. When I touch the rubber fuel line leading to the fuel filter, it is only moderately warm so I don't see how the fuel would be boiling to cause a vapor lock.

I do smell some vapors coming from the engine compartment but it's hard to tell if it's gas or just the fumes from the EGR system.

Thanks in advance for your advice.

[Ed]

Which carbs do you have? It does sound like a fuel delivery problem. Maybe your floats need to be adjusted.

[2ManyZs]

It's probably the water control valve which is stuck open and overheating the carbs, it's actually vaporizing in the carbs and not being vaporized in the lines. I had a 73 that did the same thing many years ago.

If you do a search for water control valve, you should find quite a few threads about it.

[nuteman]

I've got the flat-top carbs. I'll look into the water control valve that 2ManyZs mentioned, but I'm not sure I understand: If the valve is stuck open, then there would be coolant flowing to the carbs which should be cooling the carbs, right? Or maybe the "coolant" is so hot from the engine that it actually heats the carbs?

I'll also search other posts for the water control valve issue.

[MikeW]

I've got the flat-top carbs. I'll look into the water control valve that 2ManyZs mentioned, but I'm not sure I understand: If the valve is stuck open, then there would be coolant flowing to the carbs which should be cooling the carbs, right? Or maybe the "coolant" is so hot from the engine that it actually heats the carbs?

I'll also search other posts for the water control valve issue.

If your '73 flat tops are like earlier models the carbs actually have a insulator between them and the intake manifold. Therefore the carbs themselves do not directly get hot like the rest of the engine and the water that flows to them is actually used to warm them up, not cool them off.

[nuteman]

Before I try to block water to the carbs (which I'm not quite sure how to do, even after reading the other posts), I'd like to check for vacuum leaks.

I know how to do this on my motorcycle - just spray carb cleaner everywhere (with the exception of the air cleaner mouth) and see if the RPM changes.

Is it the same procedure for my 240Z?