[JamesWnew]

Bud's got a 68 302 that we can't find the problem with. When it's cold, it starts and runs smoothly. As it gets warmer and finally up to regular operating temp, it progressively runs rougher, not wanting to idle smooth or accellerate.

Both intake and carb have been replaced with new units. It has a pertronics in it's distributor, but it worked fine when installed in another vehicle.

Give me some ideas to go check.... wiring? vacuum? coil? I don't understand why it runs smooth cold but rough when hot.

thanks

 

[jfstang]

Timing ok?
Start at baseline of 6 degress BTDC and see.
If timing's okay, then it sure sounds like carb's not set right in the choke or fuel mixture. Is it blowing black smoke when warm? That would mean the artificially rich condition making it run nicely when cold is not adjusting back to the leaner mixture for warmed up running, so engine runs too rich when warm.
Vacuum leak anywhere?
If there is one, the rich mixture upon cold start would overpower the leak and let the engine run sufficiently rich to operate okay. As choke releases, the mixture goes more lean and a vacuum leak might become more apparent. Spray some WD40 or similar around the carb or various intake gaskets at slow idle, see if it runs a bit better. Then you know its a vacuum leak.
Just some general ideas, hope that helps.
John

 

[AMR66]

I have a 66 with a 68 302. Mine did the same thing and I replaced the magnet Assy. in the Pertronix (the sleeve) and then it was fine. It's part #12813 and it cost $24-$30.00.

 

[JamesWnew]

thanks...I'll pass it on.

 

[JonK]

As above, check to make sure the choke is fully opening when warmed up, may need adjustment. Have him check the vac advance on the dist., it may be 40+ yrs old and the diaphragm may be cracked, mine was. Remove the dist. cap, find the 'arm' that extends from the rear of the vac adv. to the dist. plate. Pull the vac line from the carb, suck on it as hard as you can - the arm should pull into the vac adv. changing the adv. in the dist. if it doesn't = bad vac adv. and it's causing a vac leak at the same time. They are available at parts stores or from mustang catalogs, the parts store ones have an adjustable screw in the nipple.
Jon

 

[MT]

If the choke checks out, I would look at the coil next.

 

[jfstang]

+1 on the coil also. I had to replace the coils on my ancient Evinrude because while it ran fine cold, after 10 minutes it was deader than roadkill. The coils simply cracked with heat due to age. I replaced them and the old thing runs like a charm.
Same thing happens to Mustang coils if old enough. Easy fix if that's the case.