1970 mustang ignition problems

It sounds more like a starter circuit problem than an ignition problem. I would check the condition of your battery cables first. You said you changed the starter, but don't rule out the possibility of having gotten a poor-quality rebuild. I had a similar problem on my '72. I rebuilt the starter myself, and it has performed flawlessly ever since. The old Ford starters don't work as efficiently once they get hot from the motor, and small discrepancies that don't cause problems when they are cold will manifest themselves after a good warming-up. (In my case, it turned out one of the brushes was slightly misaligned, causing it to jam in the guide when hot.)

warm up or run the car as usual and instead of using the key to crank it over jump the + side of the battery to the S terminal on the solenoid (small stud closed to the battery) with a short piece of wire. notice how it turns over. now try the key - it should be the same. if it is poor in both cases do as suggested and replace the battery cables(all 3) and make sure you have a good engine ground from the chassi to the engine block with no grease, rust or paint between the cable and body/engine block. It might also be prudent to test your alternator to make sure its is charging and your battery to see it can carry a load. Parts stores will test it for free - remember - an alternator can put out 12-14V and not still not produce adequate amperage to charge, and a battery can show 12v and not pack enough joules to support a load(starter)
Just a few suggestions
Joe

Thanks for the replies. I replaced the battery about two months ago but did notice that the battery cable that goes from the solenoid to the starter was a little rusty. I cleaned it up with some sand paper but did not do it with any other cables. I will have to try the wire to jump it and I might go ahead and pull the alternator off to have it tested. Question on the alternator, I have a small gauge orange wire with a connector on it that is not connected to anything. I have looked and have yet to find another wire that it would connect to. Is it not used or do I have a wire missing.

Can't help with the orange wire, but there is a link to wiring diagrams on the main page. It sounds like you are on the right track with the cables. If you can visibly see corrosion on the outside, you can be sure that it has penetrated into the cable strands. That's one of the "small discrepancies" I mentioned earlier that may not cause any problem when everything is cold.

Thanks for the help. I am going to get new cables today. I think I am going to go ahead and convert my points to electric in the distributor as well.

I installed a petronix ignitor 3 with petronix flame thrower coil. Car fires up like a champ and now I can shut it off and restart it immediately. It is nice to be able to stop somewhere and not be paranoid that I will get left stranded. I bypassed the resistor wire which now gives me 12v to the coil. After the car is warmed up if I stop at a red light or stop sign the idle drops irratically like it is mis firing. The engine sounds great and is running strong unless I am at a slow speeds and then but my foot in it, it will start to hessitate and sounds like it might die. If it put it in neutral or park the erratic idle goes away.

might have to either adjust your timing or your fuel mixture

What should I be at on timing. I think I am about 10 degree at 1,000 and 32 degrees at 3,000. That was the last numbers I read somewhere and that I don't want to go above 34 degrees at 3,000. I will have to look into the mixture. I never adjusted it since I swapped the heads.

Either timing or your alternator is not recharging your battery enough at idle. I also have a 1962 impala, and if left at idle to long, the generator light starts to flash

Also, make sure you have to vacuum leaks and that you plugged your ignition vacuum lines into the right ports. I believe mustangs use ported vacuum, NOT manifold vacuum. Good luck!:bigthumbsup

initial timing (set at idle) should be about 6-8 Before TDC total timing should be around 30-32 i believe? not sure about total timing