If this was from a diesel engine in your JD you do NOT have to worry about carbon monoxide since diesels do NOT produce enough to affect a human, not that I am endorsing any long term continued human breathing of diesel exhaust due to the carcinogenic soot and PM<2.5 particulate matter.
However, if it is a gasoline motor, there is enough carbon monoxide in the exhaust to kill 25 human beings in less than 15 minutes.
Diesel compression ignition engines typically produce less than 0.1% CO, whilst petrol spark ignition based engines produce 5%-7% CO when tuned up properly (more when out of tune).
Don't worry about CO if your engine is a diesel, but if it is a gasser watchout! [img]/forums/images/graemlins/blush.gif[/img]
http://www.cdc.gov/mmwr/preview/mmwrhtml/00050544.htm