Apologies for the poor-quality post previously, I was really out of it but I felt like I needed to post something.
I think the few rides I have taken on the bike have given me enough information to give a bit of feedback/observations on the 190 engine.
Like most of the pit-bike-sized engines around, the 190 doesn't really idle smoothly... It doesn't idle
roughly, just not smooth. By that I mean the engine is going putt-putt-puttputt-pu-pu-putt-putt-putt instead of a "normal" idle of putt-putt-putt-putt. I don't know for sure, but it think the combination of little-to-no intake piping, low speed, and no load make the engine kinda miss once every... 3-7 complete engine cycles.
The carb that came with the 190 is a Chinese copy of a keihin PE28 carb and (I am 90% sure of this, but check your jets to be sure) uses
these slow jets and
these main jets. I think, but am not positive that
these keihin main jets will also thread in to the main jet tube and work MAYBE. My carb came with a #40 slow jet and a #115 main jet. I didn't record the needle# or the clip position.
I don't have any information on the AFR ratio for these jets; I still have yet to install the AFR gauge on the bike. I've either been too eager to ride it or busy with something else. I can say that the engine responds very well in all running situations I have put it under except one. There is a miss around 4-6k rpm regardless of throttle position. I don't know if this is an ignition or fuel problem, but I have read of other people having the same miss at around the same engine speeds. Other than that, there has never been a fueling issue.
The engine starts up with the choke on within 2 revolutions every time. With the choke on and the air temp ~67F the bike idles at about 4-5k rpm. after about a minute of running, the engine will start to sound a little boggy and rich. That's when I turn off the choke. I have the idle set around 1500-2000 rpm. A little high, I know, but the engine likes it there and responds very quickly to all but the most violent of throttle snap-openings. Since, as described above, the engine doesn't idle smoothly, using an AFR gauge to tune the idle would probably be futile. I've read about mechanics using a vacuum gauge to set the idle mixture, so I'll give that a try. Also something to note about the keihin PE28 carbs - the low speed mixture screw, NOT the idle screw, meters how much air goes into the engine at and around idle speeds. Adjusting an air-mixture screw, in my experience, is a bit more finicky than adjusting a fuel-mixture screw. When I was using a VM22 carb that also has an air-adjust screw, I was running about 1/4 to 3/4 turn from fully closed to get the idle just right.
At in-town speeds of <35 mph, up to 6k rpm the engine, as geared (I think 16/34?), feels much like my scooter felt after I put a big block kit on it; feeling the same amount of torque, just add 3-5 mph to whatever speed you felt you were doing with the smaller engine. I don't know if it is my lack of experience with bikes or perhaps a poor fuel mixture, but I have to rev the engine up to about 6k rpm when taking off and SLOWLY release the clutch or else it will stall. It could also be the new clutch is being broken in as well. I'll choose me and my lack of experience as the main cause of feeling lack of torque on take-off. In situations like this that have many possible causes of a certain symptom, If I am anywhere in the "might be the cause" list, I just automatically choose myself as the cause of the symptom. I'm usually right, as well.
In contrast, once the engine is above 6k rpm, the torque and the pull from the engine increases precipitously all the way to 10k rpm. Seriously, with how much the 190 pulls at wot, I am thinking that the 125 was very held back by the factory quiet/restrictive exhaust. It pulled as hard at 8k rpm as it did at 4k rpm. I might temporarily put the factory 125 exhaust on the 190 and see just how bad it is.
When the engine is up at those higher rpms, the entire bike and engine buzzes, vibrates, and shakes and I can't hear the intake or exhaust over the mechanical engine sounds. Now, I don't mean the engine is vibrating the mounting bolts loose, I mean the lack of a counter-balance shaft makes this engine, the bike, and everything touching or connected to either of those vibrate. Nothing on my bike has come loose except for a cell phone holder. Don't worry, I didn't have a phone in there at the time.
The transmission shifts quickly, smoothly, and effortlessly. Only twice have I accidentally shifted into neutral instead of 2nd. It is still difficult to get into neutral with the engine running and the bike stationary. I suspect that will improve with continued use.
I don't know if, again, this is either my fault with lack of experience or just the way things are, but it has been very difficult to keep the engine at a steady operating state in lower gears at lower speeds. What I mean by that is below 35mph in any gear but mostly in the lower ones, the engine wants to accelerate or decelerate (as well as jerk the bike when going from decel to accel), NOT run at a steady speed. I really don't know if that is inherent to this engine or just engines above a certain size. It has certainly given me cramps in my throttle hand, having to try and precisely control input.
The exhaust system I am using is too loud for my tastes. I have only run it with the silencer in the muffler, I don't dare take it out. I'm going to try and modify the silencer to reduce the volume a bit. The silencer that is in the muffler now only has a narrower diameter pipe for the exhaust to exit through (like
this but without the holes drilled in the sides of the tube.) I want to drill holes, like in the linked piece, to force the exhaust gases to flow through smaller, but many more small holes. I also want to try cutting slots in the pipe instead of holes and see what happens with that. If none of that cures my sore ear's woes, then a muffler re-pack and possible baffles are the answer. At the extreme end, I could buy and install a different muffler. Now that I have an exhaust system that comes in pieces instead of all welded together, I can change out mufflers with the same pipe size, but that is only if everything else fails.
I have ordered some filament for my 3d printer so I can attempt to make a "backpack" for the speedo/dashboard. The big round taped-up AFR gauge, while perfectly working, is a bit too... it's just not what I like to see when looking at my bike. I am going to try and make something that will ziptie/glue/something to the front of the speedo (the part that all the bugs hit) and have the numeric AFR readout, some number of colored LEDs to indicate AFR at a glance, numeric battery voltage, and maybe either a numeric temperature display or just a temperature warning light.