My ATV Exhaust Is Getting Red

Most ATV mufflers are usually left in their raw steel form or painted black, suiting the muffler's utilitarian purpose. While the muffler's job is to quiet the roar of escaping exhaust gases, it can also warn you of an imbalance within the air-to-fuel ratio that the engine needs to operate. This is visibly obvious as the muffler takes on a dull, reddish glow when the ATV's engine warms up to operating temperatures.

Causes of a Red Muffler

ATV mufflers are typically made out of steel and capable of tolerating high ranging from 200 to 800 degrees F. A change in the engine's air-to-fuel ratio can increase exhaust gas temperatures to above 900, and a steel muffler will begin to take on a reddish glow.

Understanding Air-to-Fuel Ratios

An ATV's engine relies on air and fuel. in the form of gasoline, to create a combustible mixture that is ignited in the engine cylinder. This mixture must have a certain ratio of air to fuel to create power while minimizing combustion heat. Internal combustion temperatures rise when the ratio is thrown out of balance by the addition of more air, leading to hotter-than-normal exhaust gases. This is called a lean condition. At a minimum, the ATV's engine might feel peppier and have better throttle response at idle but will lag at higher speeds. If the mixture is too lean, the engine will overheat and increase the odds of piston seizure.

The Causes of a Lean Condition

All-terrain vehicles are normally built in a slightly lean state to meet increasingly stricter environmental requirements, allowing the ATV to operate relatively well while producing less emissions. But this state of tune is not enough to cause superheating of the exhaust gases, and most lean conditions are caused by alterations to the ATV's intake system. The inclusion of an aftermarket high-flow air filter allows more air to enter into the mixture, instantly throwing the air/fuel ratio out of balance. To compensate, the carburetor's internal fuel jets must be replaced with larger ones, allowing more fuel into the mixture and restoring balance. Without the increase in fuel flow, exhaust temperatures will rise.

Lean Conditions on an Unmodified ATV

Lean air-to-fuel conditions can also occur on a bone-stock all-terrain vehicle because of lack of maintenance. The largest factor in allowing extra air into the engine is a torn or damaged air filter, as well as intake leaks between the carburetor and the engine. Most ATV manufacturers recommend an inspection of the air filter every 10 hours of continuous use, allowing the rider to detect problems before they occur. If the air filter is damaged, it must be replaced. Intake leaks can be found by spraying a small amount of carburetor cleaner around the intake flanges with the engine running. If the engine idle suddenly decreases, the flange is allowing air in. In most cases, tightening the flange's clamp will stop the leak, but a complete inspection and replacement, if damaged, is a better choice.

References

• The Professional Motorcycle Repair Program: Fuel Systems, Volume 9; Professional Career Development Institute
• Honda TRX400EX Service Manual; Honda Motor Company
• Kawasaki KVF750 4x4 Brute Force All-Terrain Vehicle Service Manual; Kawasaki Heavy Industries