Could someone please explain the difference between to lean and to rich and also add what symptoms would appear if you had either.

 

lean = too little fuel in the fuel/air mixture. rich = too much fuel in the fuel/air mixture.

lean symptoms could be popping thru exhause pipes, especially on decelleration, running hot (pipes turning blue).

Rich sypmtoms include black smoke out exhaust and fouling plugs.

 

In order for your engine to run properly at all engine speeds, you need to have the Air Fuel Ratio (AFR) set correctly. Running too lean means that there is too much air for the amount of fuel being drawn into the combustion chamber. Too rich means just the opposite.... too much fuel for that air coming in. The simplest way to check is to examine your spark plugs. If they are very white, then you are running lean. If they have a lot of black, dry soot on them, then you are too rich. What you want is for the plug insulator (the white ceramic portion in the center) to have a light tan color, and in Harleys, you'll usually see a small white spot on it.

If you are running too rich or lean, you will need to put the bike on a dyno (or at least an AFR meter) to get it properly jetted (or programmed if you have fuel injection). There is a way to do this manually to bikes with carbs, but you need a few extra sets of new plugs, and a long, deserted road for some high-speed runs. A dyno is much easier and MUCH more accurate! I wouldn't let a stealership do it, but would rather take it to an experienced H-D tuner at a Harley performance shop. I haven't seen many dealers who had experience with tuning bikes properly unless they've been doing it for many years.

ANYTIME you make changes to the intake or exhaust system of your bike, you MUST check the the AFR since those changes will usually change your air and fuel requirements. Failure to do so may end up in fouled plugs at the least (running rich), or major damage to your engine in the worst case, usually when running too lean.

Also, DO NOT try to compensate for bad plug readings by changing to a "hotter" or "colder" plug. This will only cover up the real problem and can damage your engine. They do not create a hotter or colder spark, they just change the amount of heat removed from the combustion chamber. ALWAYS run the plugs recommended for your engine. I prefer Harley's plugs (not the Screechin Beagle ones.... waste of money) since Champion makes them to Harley's specs and they have a heat range not available by any other plug manufacturer. Actually, I never use ANY SE parts. They are usually of poor quality and are made overseas. The Harley plugs are designed specifically for Harleys. Don't fall for the fancy split-fires or platinum plugs, either. They do NOT work any better than the stock plugs... they are just "snake oil" and are designed only to empty your wallet.

Here's a good link for explaining plug reading (and lots of other great Harley performance info):
http://www.nightrider.com/biketech/spkplghnbook.htm

 

Spectrexx,

How do u read the AFR after the bike has been dyno'd? What is the dividing number between rich/lean?

Thx!