TEXMudder's Site

Home	Quads	Truck	Riding Pics

Service Tips	Mud Spots	Scheduled Rides	Links

How to tell if you are lean or rich

Troubleshooting the acceleration curve is where the most time consuming problems occur. A good rule of thumb is if you have a problem while asking for horsepower, (accelerating or adding throttle) the problem is most often too rich. If you have a problem while not asking for horsepower, then you are probably lean.

If the trouble spot is more noticeable when engine is cold, you are lean. If your problem gets worse as it warms up, you are rich. Restrict the air entering the engine a small amount at a time by wrapping the filter with duct tape or a shop rag (be sure to put the air box lid back on before testing or your results will be invalid). If the problem gets better, you are too lean. If the problem gets worse as you restrict the air, you are too rich. Once you find the problem to be rich or lean change the main jet in the direction necessary.

If you suspect you are rich, (which is likely if you started with a large main jet and are working down), uncover part of your air box and see if it runs better with more air. If yes, you are too rich.

You can also check your spark plug to see if carbon is collecting on the tip. This should properly be done after a flill throttle run through the gears, cutting off the engine before deceleration, then coasting to a stop. If carbon is collecting you are too rich. (This is why I like to install the new plug after finshing with the carburetor.) If the plug is pure white you are lean.

If the engine runs better when cold and gets worse as it warms up, you are rich.

If you think you are too lean you can do any of the following. Temporarily replace your K&N filter with your factory foam filter and see if your engine runs better. If so you are lean. (You have decreased airflow when you replaced the K&N).

If you have modified your air box for more airflow, tape up the new opening and see if it runs better. If so you are lean.

Restrict air inflow through your filter with one wrap of duct tape, or by wrapping 1 or 2 shop rags around your air filter and securing with a rubber band or bungee. If engine runs better you are lean, if worse you are too rich.

If the engine runs better with choke slightly closed (on) you are lean.

Once you have decided whether you are too rich or lean, change the main jet and/or fuel needle setting in the correct directions, depending on where in the RPM band the problem occurs (see diagram below). The bigger number main jet or groove settings are richer than smaller numbers. The following carburetor adjustments have influence on the indicated range of throttle (in other words don't expect a change in main jet to make much difference at idle or a needle groove change to affect wide open throttle). Decide where the problem is and adjust the component that affects that RPM segment.