At what speed did they run your truck? And in what gear? Are vehicles classified and tested by a Weight Class? They may have run your vehicle at a higher weight class than it should have been. Does that system require a retro-fitted PCV system? If so, change your engine oil before the next test. Did you have your choke on during the test? Even a small amount of choke during a running test will cause a large increase in CO. Make sure the choke is fully open when the knob is fully against the dash. It was not uncommon for the choke wire to break at the carburetor attachment, then someone would pull choke lever far enough to re-attach the choke wire. The 'little bit' may leave the choke slightly off the fully open position. What was the CO level from the test?
Before taking your carburetor apart, make sure the air filter is clean. Otherwise, adjusting the float level down a little, or going to smaller main jet may help. I think those carburetors typically ran with about 3%-3.5% CO at cruise- that is about a 13:1 air-fuel ratio, just above the rich-best-power mixture. If I remember correctly, your carburetor has a metering rod setup for power enrichment. If that spring is weak, the power circuit will turn on sooner than it should. The inspector may have been running your truck at such a condition that it was operating in the power circuit, in which case, they should be able to run it at a lighter load. You may have to argue with someone about that. And that may be like talking to a wall- but sometimes they can be reasonable.
Harvester
