I got an 87 K5 with a 38mm pwk carb, stock everything else. I can't seem to get the engine to rev up past 4000 rpm is my guess. I have been playing with jetting and that doesn't really make a difference. Carb has been cleaned and re-cleaned at least a dozen times. Floats adjusted to different heights and that doesn't help either. I just had the cylinder off to fix hairline cracks in the intake ports. Before putting it back together I did a light hone and put in new rings I had laying around. Compression test is 175 psi. I've ran out of ideas to try.
This engine got put in a quadracer frame. I ended up modifying a quadracer 250 pipe to fit the 500 and the small frame. I'm wondering if the length between the engine and the end of the pipe would cause my issue above? The pipe is way fatter than the 500 pipe but is considerably shorter from end to end.