Actually turning the CO2 screw clockwise (to the left) richens the fuel mixture, and turning it counter clockwise (to the right) leans it. What you're doing is raising or lowering the fuel metering piston inside the fuel distributor relative to air sensor plate movement. The CO2 screw has a 3mm hex allen head. You'll need a long pattern wrench to reach it. Remember that Lambda will counteract some effects of the CO2 screw (engine warm, not full throttle). Once (and only once) I saw with my own eyes properly functioning CIS and Lambda systems compensate for a missing plug over the CO2 screw acces hole! All other times it does indeed create a vacuum leak. Some PRV's have a small metric bolt (4 or 5 mm) in this hole by design. Without removing the cylinder heads, looking at your spark plugs is indeed the only way to tell what's going on inside your cylinders. Their condition can indicate improper fuel mixture, ignition timing issues, vacuum leaks, ring wear, etc: http://www.specialtauto.com/delorean-images/sparkpluglooks.jpg http://www.specialtauto.com/delorean-images/sparkplugana.jpg Bill Robertson #5939 >--- In dmcnews@xxxxxxxxxxxxxxx, Louie Golden <louie@xxxx> wrote: > My car gets roughly 20 city and 30 highway....... > To lean the car out remove the airbox which houses the air filter. ........Anyways, after removing the plug you simply stick an allen head wrench down into the hole and you will find the fuel adjustment screw. I can't remember the size of it off the top of my head... sorry. To lean the car turn the screw left, to richen the mixture turn it right.