cruiser
Well-Known Member
Hi All: Here's one for you expert slant six tuners. I have an interesting thing happening with my 225 in my 1974 Duster (torqueflite auto). First of all, I just love the motor. It runs great and has plenty of power for my car. I've restored it completely stock. The replacement 1974 model year motor has 100K miles on it and has good compression. The head and valve train were overhauled 5K miles ago. The exhaust system is totally stock, including the resonator which came automatically with the Noise Reduction Package. The carb is a rebuilt stock one barrel Holley 1945, stock choke setup. New clean NGK ZFR-5N plugs with gaskets removed, gapped to .035" as the factory shop manual recommends. Here's the problem, if it is in fact a problem at all. The car has a very nice butter smooth idle when warmed up. Idle RPM set to the factory recommended setting. If I stand by the exhaust pipe and listen to the exhaust, it "chugs" or "puffs" as it idles - maybe one or two chugs every ten seconds. The engine doesn't seem to slow down when it's going this. I've adjusted the idle mixture screw, which will increase or decrease the amount of "chugging", but I can never find that sweet spot where it completely goes away. I'm baffled. Do these individual "puffs" represent a failure of a cylinder to fire at that moment? if so, it doesn't seem to slow the engine down. Or is this "puffing" actually normal with a resonator equipped exhaust system, and it's not really missing at all. I just can't figure it out. Ideas? Slant Six Dan, if you're out there, please weigh in. Thanks, everybody!