Trying to get my 77' Chevy pickup(250 ci.) through emissions. The motor has 300,000+ miles on it, so I don't want to make any significant repairs to a motor that wont last, but I am failing emissions. The first emissions trip, it blew 719 in hydrocarbons after the precondition, with the standard being 250. At the same time, my carbon monoxide was only 0.02 with the standard being 2.00. Since the truck sat for 4 months, I drove it 120 miles down the freeway to clean it out. I also tried to lean the carb, but it has only one adjustment screw. I turned the one screw in about a half turn. Back to emissions. Now my hydrocarbons are 632 and my carbon monoxide are 0.01. It seems strange that my carbon monoxide is so low while my hydrocarbons are so high. My temporary tag expires after tomorrow, and I cant get anymore so I need to pass tomorrow. I still need to go over the entire ignition system, but are there any tricks I could also try? I have two more shots at emissions, so I figured i would try the ignition system, new airfilter, and an oil change. If that doesn't work, I'm going to try denatured alcohol at about 25% and 75% 91 octane. Anyone have any expiriance with forceing a vehicle past emisions?