Okeh, that doesn't mean you need to buy a bunch of upgrade parts or swap in a V8, it means it's time for some relatively minor, easy tweaks under the hood and a good, careful and
complete tune-up.
Do the
Fuel line mod. Make sure your fuel filter is reasonably new and not contaminated (and has a metal housing, not glass or plastic). Make sure the fuel tank and the in-tank strainer aren't full of crud.
Make sure your manifold heat control valve isn't stuck; see
here. Make sure your thermostatic air cleaner is intact and working correctly.
Pay more attention to the carb than just a quicky gasket kit. The Holley 1920 carb that came on most '71 slant-6s contains a float that over time will absorb gasoline and grow heavy -- then the carb runs rich and causes problems like you describe here. Truth to tell, I really dislike the '70-'73 Holley 1920 carbs; they are especially prone to bitchy problems like this even if you throw a ton of effort and time into them. The '70-'73 Carter BBS, also used on some Slant-6s from the factory, is a much happier-running carb and its float won't absorb gasoline. "Remanufactured" carbs (of any make/model) tend to be junk not worth messing with no matter the price; if you can afford it, nothing runs like a new carburetor, and
this one would be ideal (there's a "make offer" option on it, so maybe the seller will come down some).
Whatever carb you wind up with, carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted
here for free download.
Tune-up parts and technique suggestions are in
this thread, and you are probably due (or overdue) for a
valve adjustment.
The '71 cars (plus '70 California) have a fuel vapour containment system that can cause or aggravate hot idle/hot stall problems. Read all about it (and what to do about it)
here.
Beyond that, the first upgrade should be the
HEI upgrade .
If some or all of this seems bewildering to you, get the three books described in
this thread.
