If you're flying a paramotor with a stock Solo 210 exhaust, the black box, take warning. That muffler will break, sooner or later, you can count on it. The muffler typically breaks at the cast iron exhaust mount flange. There is usually a cheap steel safety strap that attaches the muffler to the motor. If you're lucky, the safety strap will last long enough for you to shut the engine down. If it doesn't, the muffler will fall into the prop, which usually destroys the prop and at least half of the cage.
You can replace the muffler with another stock black box for about $60.00, but it will have the same problem. Or, you can buy a tuned exhaust system for about $300.00. To upgrade to the tuned exhaust requires the stock cylinder head to be replaced with a larger one at a cost of around $200.00 or more. The upside is more horsepower, but it is a little expensive. Of course, the tuned system still has a tendency to break.
I was satisfied with the performance of the stock 210 and did not want to spend the money to upgrade the exhaust system. Instead, I improvised a mount to eliminate the breaking problem. In addition, I recently added a silencer to the stock exhaust that lowered the noise level considerably. It is the chrome pipe in the picture.
The modification, as you can see in the picture, involved the welding of two brackets to the muffler. The silencer is also visible in the above view.
The straps are made from 1" by 1/8" stock available at the local hardware store. Mount the muffler to the engine, locate and mark the straps, and then weld them to the muffler. It is important the straps do not apply any tension to the cast iron muffler mount when they are tightened down. When correctly installed, the mounts have to be guided into position first, the muffler mounting bolts installed and tightened, and then the strap bolts tightened. The straps reduce the difference in vibration between the engine and muffler. If the inlet port were in the middle of the muffler, instead of at one end, there would be less of a vibration problem.
The next step it to beef up the mounting flange. As can be seen in the photo, this is accomplished by welding a piece of the steel strap between the iron mounting flange and the muffler. While you're at it, double the existing weld in the area of the mounting flange. Be careful not to weld in the area of the mounting bolts, or you will not be able to install them. If the mounting flange still manages to break, the muffler will not go anywhere.
Still got the welding machine out? Let's install a silencer. You will need a VW bug exhaust tip; they cost about $6.00 new. I used the VW tip because they are a straight through design that would not add any backpressure. The harder part to find is a steel elbow or two. One is needed to direct the exhaust flow from the stock outlet into the silencer. The other can be used to direct the hot exhaust gas away from the fuel tank if need be. Find one that will fit the inside or outside of the VW silencer, it doesn't matter which. Weld it to the silencer first. Make adjustments to the remaining length of the elbow so the silencer will contact the front of the stock muffler. See the picture below:
This is done so the silencer can be welded to the face of the muffler; the more welds the better. Make a bracket from the steel stock to support the silencer from the bottom of the muffler as seen in the picture. When finished, the propeller should make more noise than the engine, which will make everyone happy when you are flying around enjoying the view.
The muffler-bracing project is a bit labor intensive, which means it will not be cost effective to produce commercially by any manufacturer. If you cannot do it yourself, or don't have the tools necessary for the project, I could probably do it for you. Send me an e-mail at firstname.lastname@example.org