Starts Good, Idles Poorly, DIES!

Hawkk72 · Jan 8, 2008

Have a 72 fastback with a 302, 4V Edelbrock intake and carb and factory A/C. Car starts fine, idles in high but when kicked down runs really rough and then dies when put into gear. The distributor is 100% advanced and I don't know where to find the timing mark (HELP). I checked for vacuum leaks and didn't find anything obvious but I did discover one odd thing. When I take a plug off an unused vacuum carburetor port the idle increases tremendously. Shouldn't it be the other way around? One additional note...disconnecting or connecting the vacuum advance hose to the distributor has absolutely no effect on the engine idle! Any help would be greatly appreciated.

Hawkk72 · Jan 15, 2008

I don't know why I haven't received any replies to my post but I really need your help with this. Please point me in the right direction by getting me started on where to look first.

entdoc · Jan 15, 2008

the idle speed will increase when you pull the plug off the vacuum line, this allows more air for a leaner mixture thus increase idle speed.

My 289 is doing something similiar. It starts and idles fine, but when I put into gear(c4 auto) it shuts down immediatly like the torque converter is locking down or binding. It even does it with the rear wheels in the air and free spinning. At high idle speed ,1600 or so I can get it to run in gear. I am confused to say the least.

Fast63 · Jan 15, 2008

I don't know what you mean by your distributor being "100% advanced". How far out are the turns on your idle mixture screws up front? Are you sure your idle speed screw is set right? You need to find out exactly how much timing you have because timing is fairly critical. Some cars do not get any advance from the vacuum advance at an idle, so taking off the vacuum line from it doesn't necessarily mean anything. Which port is the vacuum line hooked up to on the carb? You can test the vacuum advance module by sucking on the vacuum line while it's hooked up to the vacuum advance. If it holds air, it's still working, if not it's shot and needs replacement.

jikelly · Jan 15, 2008

Is this a recent occurance? Did you change anything on your engine before it happened? What type of choke do you have?

I've experienced similar things in my 73 with a similar carb to yours. Generally that signaled it was time for a tuneup of the carb and/or fuel mixture and choke adjustment. Generally this happened to me in the winter when temps dropped, or when the carb became too dirty from all the sand blowing around here to operate properly. That stuff likes to get into the little passages inside your carb that allow it to properly meter the air/fuel mixture.

Hawkk72 · Jan 15, 2008

I really do appreciate all the replies and suggestions. Some additional information: the choke is automatic, and nothing was done to the engine before this started. I've tried adjusting the idle mixture screws but that really hasn't helped as far as the stalling out problem goes. As I said I don't know where to find the timing mark on the engine so I don't really know where it's set. When I said 100% advanced I meant that after loosening the collar locking bolt I can manually move the distributor all the way advanced and there is no change in idle speed.
I wanted to mention that sometime when the car is idling I can hear and feel a "thumping" coming from under the car. Looking underneath I can't see anything happening but it feels as if something is hitting the floorboard. Could this be a torque converter problem as someone mentioned above? The tranny is an FMX. I have a 289 w/tranny in the garage off a 67 Cougar, but not sure what kind of tranny it has. If it was a C4 or C6 would it bolt up to the 302 in the Mustang without any mods? If the problem turns out to be the torque converter would they be interchangeable? Forgive me if any of these are dumb questions!

Rusty67 · Jan 16, 2008

The Cougar trans should be a C4 and it will bolt up to any small block Ford V8. I'm not sure if you will need a different length drive shaft or a different tranny cross member.

Hawkk72 · Jan 16, 2008

Does anyone know the answer to that? I have a Cougar drive shaft that goes with the trans.

Starts Good, Idles Poorly, DIES!

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