I have a 67 Mustang, with a 68 289 motor. I think it is from 68, not really sure. The problem is when the engine warms up, it will get really doggy (loose power), then if I let it cool, it will run fine until it gets to a certain temp., then it will get doggy again. Already replaced the air filter, carb, and fuel pump. What is wrong. Thanks.

 

maybe your engine is running too rich, with what it can cope if it's cold but not when warm ? Id check on:
a) in case you have breaker point in distributor, check dwell
b) then check ignition timing
c) then check if your choke oiperates properly (the top butterfly in carb needs to be fully open when engine is warm)
d) then adjust the idle mixture when warm
e) then spray some WD 40 around the carb when engine is running (not into the carb or airfilter)
if engine idle changes you are pullig false air at where you are spraying. Fix that leak

 

oh and check the color of the spark plugs indicating rich/lean/detonation ...

 

Thanks for the info, hopefully one of those things work.