AFR's

raymond said

I am using 98 here in OZ, we leaned it down twice on the dyno and picked up around 30 HP but it was still in the high 11's on the AFR reading, I've gone leaner one more step but it has got soft on the hit and the 60ft. has dropped off, problem is I'm running an 850 TQ and it it doesn't like being that lean on the launch, I've slowed the secondary air door opening down but it's really not happy. I'm trying to source a decent size double pumper to get it to leave the line like it used to.

Click to expand...

Your AFR readings should correspond with the colour of your plugs. If you richen your mixture beyond stoich (14.7 AFR) you should get colour on the plug because the oxygen cant utilize all of the carbon. What does that mean? It means that the left over carbon "should" manifest itself on the plug as light tan to black depending on how rich past stoich.

If you are really at 11-1 AFR your plugs should be black and if they aren't there's a problem with the combustion. The spark plug shows you what the AFR is at the plug at the time of ignition. Remember its the AFR of the gas not the liquid that matters and if the mixture at the plug at the time of ignition isn't very good then you will get a rich reading (02) with a clean plug.