bike "popping" under acceleration

hello i have a 1980 cb750, did new plugs on it and i have a mac 4-1 exhaust. under moderate/heavy acceleration the bike will "pop" multiple times and the acceleration will break up about 3-4 times when i pull it through a gear. i hear this a symptom of the bike leaning out but i didnt think just changing the exhaust only will cause the bike to lean out this bad? is there anything else that can be causing this?

you didn't change to a larger main jet when you put the exhaust on? If not then thats pretty much the main solution right there. Anytime when you change the airflow characteristics in or out of the engine you have to tune the carbs. There just isn't any way around it.

Get to those jets quickly too! My first bike was a 1982 CB750K (very nearly the same bike) and, being that it was before I knew very much about bikes, I let the jet issue go with that same Mac 4-into-1 header and destroyed the engine in just a couple hundred miles. Granted, it had that setup when I got it and may already have had some problems when I got it but it went from the condition that you are describing to un-rideable in just a few hundred miles.

I would suggest not riding it until its fixed.

anyone know the stock jet sizing for this bike? how bigger should i go. it has the stock air box still

Read this:

http://www.dotheton.com/forum/index.php?topic=16745.0

Wont give you the answer, but it will guide you in the right direction.