I bought one of the Launtop 186F engines and can't speak much towards its long-term reliability as it only has about four hours on it. The only real problem I'm having is it cannot reach rated speed of 3600 rpm. It can do about 3250 rpm before sputtering/missing/white/light gray smoke. I checked the timing and adjusted the valve clearance. Timing was right on the money. Valve clearance was a little loose at 0.009-0.011" vs. the 0.006" as specified. It may have something to do with the higher elevation I'm at (6200' asl). I'm thinking the intake is insufficient to allow the high flow rates required at the higher speeds but can't confirm for sure. I suppose if I put a gauge on the intake and see what it's doing at the higher rpm that would help but I haven't gotten around to that yet.
Anyway, I thought I'd mention an interesting comparison of these engines I thought about recently. In additon to the Launtop 418 cc diesel, I also have a 419cc China-Honda knockoff (model XP16HPE) in a generator unit. Both engines are the basically the same displacement (the gasoline engine has a slightly larger bore and shorter stroke) and operate at the same rated speed. The gas engine is 16hp@3600rpm according to Maxtool.com, the Launtop I'm finding has multiple claims at various speeds. Some sources say 10 hp@3600 rpm and 8.6hp@3000 rpm. If you look at the performance curves (attached), the speed and torque ratings don't add up to the correct hp ratings. For example, the claimed torque at 3600 rpm is about 25Nm. Since power is speed x torque that equates to about 12.7hp after you do all the conversions, so I'm not sure what to think on its actual output. I do find it surprising the gasoline engine is rated at 16hp at the same speed though. According to Maxtool.com, the XP16HPE has torque output of 21 ft*lbs which is more than the diesel has. However, if the gasoline engine has 16 hp@3600 rpm, the actual torque should be more like 23.3 ft*lbs (at 3600 rpm). So either my math is wrong or none of this makes much sense.
Gasoline engines do appear in general to have more power available for the same displacement but this appears to be primarily due to being rated at higher speeds which diesels don't typically attain. With that in mind, I find it hard to believe a gasoline engine at the same speed and displacement puts out more power than a diesel and in this case, even more maximum torque. Thoughts?