I have a 1978 212 that has been giving me issues. It will run beautifully for some time (3 or 4 mowings) and then start loading up for about 15 seconds at a time then clear up and run for maybe 20 seconds up to 5 minutes then do it again. When it does it it puffs black smoke and of course, giving it a bit of choke only makes it worse. It usually will act up when turning but not always and direction doesn't seem to matter. I put myself through college working on these things but this one has me baffled. Carb is clean, have changed needle and seat and the float and checked for cracks. Float is set very low (normally I set them just above level with the carb upside down but this one is set at a pretty good incline) and it appears to help but only for so long. Electrically this thing is fine, have switched out coil, condenser, points, plug, plug wire etc with known good parts and it still does it. About the only thing I haven't changed is the fuel pump. I haven't ever seen one put up too much pressure, only too little or leak. Next time I have time I will figure out a way to check fuel pressure. Have any of you guys ever run into something like this? Thoughts? Ideas?