I'm new to the forum, and have recently purchased a 72 Convertible with the Mach 1 Package. Fun car, but we're still getting to know each other. What I know now is that she doesn't like the desert! Originally thought I had an electrical issue, but now I'm really stumped! This is driving me nuts!
Runs like a champ when cool. After it's hot, it will rev, and idle OK, but when you put a load on it, it just dies. Heres what Ive done since the problem began, and what I am observing:
Parts New carb (already had, so put it on
Hard metal fuel supply lines (at carb)
New coil (Mallory resistor coil)
New electronic distributor internals (Mallory)
Observations The fuel bowls are full
Timing at 12 btdc
The fuel filter is nice and full when cold, but as temps rise, fuel filter drains to near empty, and I can see irregular spurts of fuel every few seconds into the near empty filter. However, bowls are full, so fuel starvation should not be a problem, correct? Or, could pump cavitation cause an issue, even with full fuel bowls?
Once engine reaches max temps, at idle, if I try to hit the accelerator, it just dies.
I have a Carter fuel pump with about 2k miles from another project, which I could try. I also have recently rebuilt the old Holley 1850/600, which I could swap, but somehow I don't think that's the issue. I was having this problem with the old carb before rebuilding it.
It's interesting that your fuel bowls are full, but I still think you are looking at a classic vapor lock situation.
If you want to test for this easily and cheaply, (and fix the problem at least temporarily) buy a Mr. Gasket 12S (or similar) electric external fuel pump. They sell for about $35. Mount it at the tank between your hard line and your tank using hose. You can power it from a toggle switch.
That pump will work fine inline with your mechanical pump. You won't have to change anything under the hood.
If it's hot out, or you are having fuel delivery problems, turn on the auxilery pump and it will insure that you have adequate pressure all the way to the fuel bowls. If it's cool or even if it fails (since it is sort of a cheap-piece-o-junk as far a fuel pumps go) you don't need to run it at all. It won't keep your mechanical pump from being able to draw fuel from the tank even if it's off.
I ran one of those for a year and it worked great. It's a little noisy, but I never had another vapor lock problem. Eventually, I switched to an in-tank electric fuel pump...but that's a HECK of a lot more money and trouble to install.
If it doesn't fix your problems...I'll be shocked and amazed.
Agree it could be vapor lock, out of interest where did you buy the car from and when? How much fuel have you put in? Could be a winter fuel with a much higher vapor pressure than you would want for the dessert.
Well, for $35 it may be worth a try. However, with fuel in the bowls, how can it be fuel pressure related? I mean, the fuel is in there where it should be, right?
But you don't have any fuel pressure, or you wouldn't be seeing vapor in the fuel filter. What I think you're seeing is the pump cavitating as the gasoline is boiling in the fuel pump. Once that happens, you lose prime on the pump, and fuel pressure to the carburetor. The engine can empty the primary fuel bowl in a few seconds once you open the throttle.
Thanks Phil. It does look like the pump is cavitating when hot, and I understand that with a weak pump, fuel bowls can empty in a hurry. However, when the engine dies, the fuel bowls are completely full. That's what is baffling to me.
Even after you shut your engine down, there is still residual pressure in the line. (I got fuel in my eye finding this one out when I unseated a carb inlet needle on a motor I had just shut down.) Therefore, after your car dies, there is still enough pressure in the line to fill the bowls back up with fuel by the time you open the hood, since the engine is no longer consuming any. That's my theory, anyway.
Think I will try the electric pump. However, wondering if I should bolt up that Carter pump I have on the bench, just to see if the Autozone pump that the other guy put on has taken a dump. Wouldn't be surprised!
Ok guys, thanks for all of the replies, but it looks like I have found the problem. I let it get good and hot, and shut it down. Heard, then saw fuel squirting from carb. Looked through the temporary site plugs to see the fuel jumping around. Is this incredibly rare? I only have an idiot light, because I haven't had time to install a temp gauge in the few weeks that I've owned the car. The radiator has been drained, and filled a few times, and has fresh coolant. It is flowing and cooling. However, this is Vegas, and it is damn hot under the hood.
What should I do to help prevent this? Thanks again!
Going to try a whole lot of heat shielding material for the fuel lines, headers, and a heat shield for the carb. The exhaust also runs very close to the fuel line exiting the tank, so I'm going to shield it as well. This desert is hot. Hopefully this stuff helps! Will let you know.
You MUST have an insulating spacer between the carb and intake. Aluminum is not an insulator. If you have an aluminum spacer ditch it and get a phenolic (insulating) one. The thicker the better - 1" if you have the clearance. Don't buy the cheap generic ones as they might be warped. I have a Moroso on mine. Really doesn't matter if it is 4-hole or not but make sure the carb seals to it.
1967 Shelby GT350, dark green, 347 stroker, 5-speed, inboards, #2206
1973 Mustang Convertible, white/white, black stripes, Q-code (351C-4V), ram air.
1968 1/2 428 CJ convertible, R-code, red/deluxe red, auto, finally finished.
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