After finally getting the Express to run again, it has some problems idling and running. The auto choke (1981 NC50) isn't working, so to choke it I screw the air/fuel screw all the way in when starting cold. After it starts, I usually turn it to 2 1/8 turns out, but now it seems to be too much air and not enough gas. I found a sweet spot and it idles pretty good at about 1/8 - 1/4 turns out. Although it stays running, when I ride it around, it 4 strokes a lot and chugs out clouds of blue smoke.
When I was getting it warmed up (with the air/fuel screw all the way in), I stopped the engine after a few minutes and checked the spark plug. It was covered in carbon, all wet. This is called wet fouling, right? What causes wet fouling? A couple days ago when I got a new spark plug, it looked like it was running too lean when I did a plug chop.
After I let the bike sit and cool down for a little while, I decided to check for compression since I already had the spark plug out. I put my finger in the spark plug hole and kick it over. It pushed my finger out, so compression is good. Correct me if I'm wrong.
I cleaned all around the exhaust port yesterday and baked the muffler last fall. I inspected the head and cylinder gaskets, and there seems to be some black liquid carbon dripping from the exhaust port every now and then, but there is no exhaust leaking around the port.
So to check for air leaks, I got the bike idling okay with 1/8 - 1/4 turns out for the air/fuel screw. Took a can of carb cleaner and sprayed around all the gaskets, exhaust port, spark plug, and auto choke. The engine didn't sputter, so no air leaks? Again, correct me if I'm wrong.
I suspect that the piston rings are worn out and need replacing. I used a mirror and a flash light to look in the exhaust port at the piston rings. It seems fuel is able to pass by the rings, causing something called blowby. I'm going to get new rings and replace them in the next couple days. Is there anything else besides worn piston rings that could cause this? It's just that I'm having difficulty getting the cylinder jug off.
I hope I've given enough info.
Thanks in advance!