[73 Mach1]

I have a 1973 mustang mach 1 with the 302 (originally a 2 barrel) now a edelbrock 4 Barrel. It ran perfectly when I bought it straight out of storage a couple months ago, recently it began to act up when I would drive it in the city, it would heat up to around 200 at stoplights and upon acceleration it lacks power and when you try to accelerate harder to compensate it starts to pop and backfire and still has no power, it never dies but it does idle roughly when this happens. Once you get it up to speed it runs fine and cools back down to a normal temperature of around 190. Once you get it out on to the highway for a bit it will run perfectly fine from stop right through full on acceleration again. Yesterday I went out to start it after it had sat a few days and it took a lot of tries to get it going because it would fire but then immediately die especially if you touched the gas, i eventually got it running but it was idling at a very low rpm and very roughly although it never died again and i left it idling for nearly 20 minutes probably, it was completely warmed up when i shut it off. Any ideas on what could be the problem? I haven't even really looked at it yet. Thinking it probably desperately needs a tune up or perhaps the choke is not working properly?

 

[kenv]

Could be vacuum/timing issues.

 

[Beechkid]

Put the oem carb back on and see if that fixes the problem......I'm betting that will verify the carb issue.

 

[73 Mach1]

The oem carb is long gone haha i wish i did have it.

 

[Yadkin]

Intermittent problems as you describe points to something going on with the distributor. I would test the vacuum advance using a vacuum pump, then the mechanical advance by seeing if the mechanism is turning smoothly, and are the springs and weights intact and operational.

If that's all OK I'd check the static timing to see if your timing marks are actually at TDC of the compression stroke, and if OK then set the ignition timing at idle to 10 degrees BTDC with the vacuum advance disconnected and the source plugged.

Then I'd check your spark plugs and wiring.

Carb would be low down on my list.

 

[73 Mach1]

update: I do believe it is a major vacuum leak, you can hear a definite quite loud hissing noise coming from the passenger side of the carb from the sound of it. There are no hoses coming off this side of the carb, so perhaps the gasket between the carb and intake is blown? Is it possible for it to be leaking vacuum internally? the only thing on this side of the carb is the electric choke and i don't think it has anything to do with this problem.

 

[Yadkin]

There should be a spacer between the car and the manifold to keep the carb cool. That may be cracked, or a fitting broken off. There should be a gasket above and below the spacer and one may be missing. A lot of carb rebuild kits only come with one.