Q. What are some symptoms of rich and lean conditions?
Rich :
Sputtering or blubbering often occurs with excessively rich conditions.
The engine may have a flat or lower pitched sound.
Performance may improve in cold and dry conditions or as elevation decreases.
Performance may degrade in hot and humid conditions or as elevation increases.
Performance may improve if restrictions are removed from the inlet path, such as removing the air filter or part of the air box to allow more flow. This is only a test procedure. The carburetor should be adjusted to correct the condition.
Performance may degrade if restriction is added to the inlet path, such as partially covering the airbox inlet or snorkel or taping over a section of an open air filter. This is only a test procedure. The carburetor should be adjusted to correct the condition.
Pre-mixed two-strokes may smoke excessively or produce lots of residue (this could also be a symptom of pre-mixing too much oil with the fuel). Even four-strokes experiencing very rich conditions may produce some black smoke.
In very extreme cases the cylinder walls may become washed down with fuel and you may find that oil in the crankcase smells of fuel and becomes thinner from fuel dilution.
Cooler than normal engine temperature. This is especially easy to notice with the use of a cylinder head temperature (CHT) gauge.
Poor fuel economy.
Dark / black or wet spark plugs.
Lean :
Bogging with a sort of "buhwaaa" sound may occur upon application of the throttle.
Very lean conditions may cause surging RPM, even to the point that the scooter may not have enough power to move in some cases.
The engine may take on a more tinny or hollow tone.
RPM may hang, remaining higher than it should be after the throttle is released.
Performance may improve in hot and humid conditions or as elevation increases.
Performance may degrade in cold and dry conditions or as elevation decreases.
Performance may degrade if restrictions are removed from the inlet path, such as removing the air filter or part of the air box to allow more flow. This is only a test procedure. The carburetor should be adjusted to correct the condition.
Performance may improve if restriction is added to the inlet path, such as partially covering the airbox inlet or snorkel or taping over a section of an open air filter. This is only a test procedure. The carburetor should be adjusted to correct the condition.
Elevated engine temperatures. This is especially easy to notice with the use of a cylinder head temperature (CHT) gauge. Spark knock may begin as temperatures increase.
Two-strokes may seize or soft-seize due to the heat from running lean or it could even cause the piston crown to cave in or melt. Four-strokes can seize, but it's not a common occurrence because they are more forgiving and often display much more obvious symptoms than a two-stroke prior to seizing.
Popping or backfiring.
While riding wide open throttle, quickly roll off of the throttle to about 7/8 throttle. This should create a slightly richer than normal mixture briefly. If performance improves during this period, jetting may be too lean.