Only time I've had red hot muffler is because the valves were not properly adjusted.
Yes, I heard you state you adjusted them...
I've had to go back and re-adjust them...

That or a governor gone wild but you'd know this because the engine would sound like it was racing.

 

Red hot muffler:
1.) Running lean
2.) Muffler is wore out.

It backfires because you removed the solenoid and it's getting hot.
Pull the choke out some while running, does it still run? Pull it out more... still run ok? If so, it's running lean. Clean the carb. If it doesn't like the choke, replace the muffler.... and the solenoid.

 

Aside from the issues you mentioned, how does the engine run? Is it lacking power or seem to be running like it should?

A glowing red muffler doesn’t necessarily mean you have a problem. A lot of mufflers glow red and those that don’t are very close to it. If you’ve ever touched a hot muffler you know. It will sizzle the skin off you before you even know you’re burned. It’s a mistake you don’t normally make twice.

Does this engine use a straight flywheel key or a woodruff key? If it’s a woodruff, the flywheel will have to come off to know if the key might be partially sheared.

Read the spark plug. What does it tell you? If your engine is running hot that should be reflected in the spark plug. If the plug looks normal, your engine isn’t running hot, but you still could need a new muffler. That being said, that fact that you are getting oil and fuel in the muffler might make it harder to get an accurate reading of the spark plug.

As far as the backfire on shut down, that’s fairly normal too, especially since there is no anti-backfire solenoid on the carb. Even with the solenoid many engines still backfire simply because they aren’t shut down correctly. Without the solenoid a lot of the manufacturers recommend letting the engine idle for 30 seconds to 1 minute before shutting it down to help prevent the backfire.

For engines with a working anti-backfire solenoid, the recommendation is to shut the engine down at half throttle or higher. I always recommend full throttle. It’s just simpler and is not going to hurt a thing contrary to some who believe it will. Shutting it down at the higher RPM lets the governor spring pull the throttle plate wide open and lets in as much air as possible as the engine spins down. What little fuel might get drawn in through the idle circuit is now so diluted with air that it can’t ignite when it reaches the hot muffler. If the fuel solenoid is working correctly, the high speed circuit of the carb is closed so no fuel should be getting drawn in from it so the backfire should be eliminated.

Let us know if you have more questions or if you come up with a solution.

 

For engines with a working anti-backfire solenoid, the recommendation is to shut the engine down at half throttle or higher. I always recommend full throttle. It’s just simpler and is not going to hurt a thing contrary to some who believe it will.

It's not that it necessarily "hurts" anything so much as there is just no need to do it. The problem is most people who you tell this to simply never (and I've seen this 1000 times) use the throttle. They just leave it WOT. They start it this way, back out of the garage, throw the deck in and start mowing. Finish the job, pull it inside and hit the key to kill it. No warm up, no cool down. On and off. THAT is where the problem is. If you really think that by moving the throttle to WOT help, (it doesn't do anything BTW) then advise people to do it as they shut it off. Hit the key and push the throttle up at the same time.

Shutting it down at the higher RPM lets the governor spring pull the throttle plate wide open and lets in as much air as possible as the engine spins down. What little fuel might get drawn in through the idle circuit is now so diluted with air that it can’t ignite when it reaches the hot muffler.

As the engine slows down and the throttle plate is opened, the high speed circuit will still have fuel being drawn through it until the engine slows quite a bit below the peak torque speed, which would be somewhere around 2200/2400 RPM. Then it will slowly switch over the low speed circuit. So, it still gets quite a bit of fuel, and the faster the engine is running when you kill it, as in your suggestion of WOT, the more fuel will enter. FAR more than if you had it at a nice slow idle. You seem to think that once you kill the ignition, the fuel also stops.... (more on this in a minute as at present we are assuming to fuel solenoid) it doesn't. It still fuels the same as it would if it was running. In your example, a super lean mixture is not reached. You would be better off shutting it down at idle and pulling the choke. Even a small amount of fuel will ignite even if the mixture is lean... but if you cut the air off, there is no air to let the fuel burn.

If the fuel solenoid is working correctly, the high speed circuit of the carb is closed so no fuel should be getting drawn in from it so the backfire should be eliminated.

You don't seem to understand that the fuel solenoid is on the bottom of the emulsion tube in the carb. Once the solenoid closes the port, NO FUEL can go from the bowl to the venturi, on either circuit, low or high speed. The fuel bowl is shut off from all circuits. Both circuits pull fuel from the emulsion tube.



Best way to prevent a backfire, is to let the engine cool for several minutes...... Besides, it's better to let the motor cool off with the engine fan than to let it cool shut off while hot. Not all metal cools at the same speed. Letting it run cools the outside parts first, such as the head and jug, then the heat from the piston transfers to those cooler components cooling it. The oil cools down, the block ect, in a more uniform manner. Plus, since all components cool more slowly and uniformly while being lubricated, you don't suddenly have very hot parts inside with no oil being pumped over them to cool them. The oil that is on them sits, and bakes on. Anyone who has rebuilt a lot of engines can tell which ones were cared for in this manner just as soon as they are opened up. Brown baked on oil soot on everything. Engines that were allowed to warm and cool, the parts are typically pretty clean. Those engines will have a lot more hours on them at rebuild time than the others as well.

 

Honestly, one of the biggest reasons you get a backfire on shut down is too high of an idle. I typically set all small engines much lower than recommended. Old carbureted cars would backfire on shut down if the idle was set too high too. Anything carbureted will.

 

I just want to be sure we are discussing the same thing here. I believe we are talking about engines with fuel solenoids, the function of the fuel solenoid and how to properly shut down an engine with a fuel solenoid. Is that correct?

 

@VegetiveSteam
Go out and start an engine with a fuel solenoid. Then while it is idling, unplug it. Bet me it dies.

Anyone who has worked on a motor with a bad fuel solenoid knows they won’t start if it won’t come on. Why? Because no fuel is available to any circuit in the carb. The idle circuit is cross drilled into the main.