OK here I am again scratching my head. Here's the story, my son bought a sweet 79 F-150, 300ie, new process (wide ratio) 4spd. The body as straight as I've seen, never been wrecked, no rust, nice paint and interior. The bad, the guy cut the exhaust off behind the converter and the converter was toast! The truck started and drove, but ran like crap. Missing, back firing,no power, gas guzzeling, rough idle, you get the picture. We drove it home and started giving the motor some much needed TLC. What we done, changed oil, filter's, vacum lines, spark plug's, cap & rotor, (plug wires were new), rebuilt the carb, new exhaust, PCV, the egr is shot (temporarly blocked it, got a new one on order). Checked compression (average 170 give or take 5 psi) vacum at manifold a steady 15 at idle, a steady 23 at 1,500 rpm. Set timing 9 btdc. Everything we have done has made a positive difference. Especially the PVC, I think it might of had the wrong one in it. The beef, from idle to 1,400 rpm lack of power and it's rough. After that smooth as glass. Something isn't working right at low rpm's. Anybody have any suggestion's? Thank You

 

It has a Carter 1 brl. carb (as I think most 300 do) #73638. When i rebuilt the carb I noticed the hot idle compensatar valve assy. (only available on some model's) had been replaced with a plug. Seeing how the carb had already been rebuilt atleast once, by a professional builder.(I know this by the sticker on the carb) I assumed it was ok. Note the plug was not a good fit: The way I found it, the top rim of the carb where the air cleaner sit's. This carb has 4 holes, 3 of which screw's go into to hold the top to the body. The fourth hole which is directly above the valve assy. Is nothing but a vent hole for that assy. With that plug being a poor fit it created one heck of a vacum leak straight off the intake. With the truck running not only could I hear it, but I put my finger over it I could feel the vacum and the motor smoothed right out. JB welded the plug and life's good! Happy Day's!