I have a '74 cb 550 that I recently purchased. The bike ran horrible until I replaced spark plugs, rebuilt, tuned, and synched the carbs. Now it runs amazing for about 20 minutes then starts to hesitate and sputter (at all throttle positions). It sounds and feels like its running on two cylinders and if I give it full throttle the other cylinders will fire sporadically but at all other throttle positions it's like its running on half of what it has. Typically I let the bike cool for an hour or two and it will start right back up and run great at all throttle positions and rpms. Spark plug tips look a little white on three (2,3,4) of the cylinders and sooty on the first cylinder I have the pilot screw set in all the way (to make it run richer) and I've backed it off of the first cylinder about 1.5 to 2.0 turns and that helps (the coloring but not the way it runs after 20 minutes of riding) which seems like a pretty big deviation from all the other cylinders. The bike has a stock air box and 4-2 pipes so when I rebuilt the carb I ordered all stock jets. From what I've read so far it sounds like I should move the needle jet clip down to make the bike run richer between 1/4 to 3/4 throttle but the this will be the last ridge left in the needle.
Any Ideas?
I plan to order new MAC exhaust, pod filters, and a couple sets of larger primary jets. But i kinda would like to get it running right in its stock form first to make sure theres not an issue with another aspect of the bike that I may be overlooking.
I appreciate your help!
