I have a 1988 Subaru Justy DL. 1.2L engine carborated engine. Miles = 89,000.00. Hitachi 2 barrell. Very clean running car, no issues there. Passed state inspection last year in August. 2 months later I replaced the carb due to the gas valve leaking and killing the car at idle. Although that problem is fixed, at the time of the carb replacement I lost 40 miles to the tank. Come inspection time my vehicle is running high CO count and will not pass inspection. Some say it could be a vacuum leak, although no reputable shop can find one. I've sent the carb back in for a rebuild as it is warranty for life. The fuel mixture settings on the carb litterally have no effect on the idle or performance of the car. Could that indicate a vacuum leak? I've taken carb cleaner like some suggested and tried spraying around the manifold and vac hoses but cannot pinpoint any noticeabe difference in idle.
I also recently changed the oil, oill filter, air filter, spark plugs and have run RXP in the fuel tank. This got my CO count down to 4.8, a 50 % decrease in the previous test. I have one more free test before I have to pay a thrid time and want to make sure I've replaced all the simple things related to CO count. I'm dumbfounded how I could lose 40 miles to the tank on a new/refurb carb though.