I ran some tests with and without the exhaust extension.
Ambient temperature was approx. 35 deg. F, overcast, damp moderate breeze. Generator was put at the opening of the garage door with no obstructions near it to affect readings.
Using a Kill-a-watt meter and an infrared thermometer, I tested the generator with no extension running at medium load (1150 watts) to a heavier load (1700 watts). Temperatures in the area around the opening in the muffler were around 425 deg. F at medium load and closer to 500 deg. F at heavier load.
I attached the exhaust extension which consisted of one 6" piece of 1" dia. copper pipe and another piece 12" long and two 45 degree couplers at each end of the 6" piece coming off of the muffler.
Temperatures at moderate loads increased to around 450 degrees (approx. 25 deg. increase) while full load temperatures went up to as high as 530 degrees (approx. 30 deg. increase). Accordingly, from initial readings, the exhaust extension does contribute to higher exhaust system temperatures. If the temperatures do not become exessively high, this might not be a bad thing. Increasing exhaust gas temperatures actually helps expedite exhaust gasses thus increasing efficiency of the combustion process. At least that's what I've read in articles written about motorcycle engines. If anyone knows anything to the contrary, I'd like to hear it.
After doing the tests, I drained the oil which had approximate 6 to 7 hours on it. The original oil that came with the machine was no-name Chinese 10W30. When drained, it was brownish black. I drained the hot oil into a funnel lined with a filter I made from white paper towel similar to a coffee filter. Other than discolouring the filter, there was virtually no observable engine debris. This is one of the cleanest new engines I've owned. I'm not surprised though. A couple years ago, I bought a standard type Champion (Chinese) generator with a Honda 196cc clone engine. It was remarkably clean as well. That tells me that the Chinese appear to be making serious progress in construction and quality control building their small engines. I filled the engine with a 50-50 blend of Shell Rotella T 15W40 and 10W30. I'll run that for the next 50 hours or so before switching over to the 5W50 Castrol synthetic.
Another pleasant surprise was the fuel consumption. On exactly one litre of gasoline, the engine was run for approx. 45 minutes at 1150 watts (57.5% load) and another 20 minutes at approx. 1700 watts (85% load). That's 65 minutes at approx. 2/3rds load. Considering that I'll be using on average less than 500 watts for hours of light load applications, I'm looking forward to very reasonable fuel consumption. I'm guessing in the vicinity of 2 hrs. per litre give or take a few ounces.
Overall, I'm fairly impressed with this inexpensive little generator.
I'm surprised that fit!