I have a Ryobi Cs30 Weedeater and the muffler glows red after a minute or two of use at full throttle. I took the muffler off and air blows through freely with no resistance. I have checked spark plug for correct gap and it is fine. Air filter is brand new. I don't know what else to check, can someone please help?
The reason the muffler is glowing red is because the exhaust temperature is off the chart.
This (highly likely) means that the ignition timing is out, or the fuel mixture is too lean. One possibility on small engines that run a flywheel magneto is that the keyway/key may have damaged itself or sheared off, allowing the timing to go out. Or, the carby is gammed up, not allowing full flow of fuel.
What does this mean? Well aside from the engine going outside of it's safe operating temperature (wearing out components faster), it can also lead to detonation, which is where the fuel is igniting before the end of the compression stroke. This can result in breaking the connecting rod and lunching the engine.
It's probably a good idea to get it checked.