Motorcycle Repair: 1975 CB750 Honda, correct shade, ngk plugs

Question
I picked up a 1975 cb750 honda recently, cause my dad use to work on these all the time. Unfortunately he is not home for the month, and Im in a rut.    My dad and I did a top end job on the engine. New piston rings, honed cylinders, new guides, etc. The bike ran fine for the first 200 miles, now its doing some funny things.     *Constantly fouls plugs when first starts up (randomly fouls, no specific plug, only when cold)  *Has low range hesitation when taking off in 1st gear (like a flat spot from a stoplight, wants to kinda die, even when warm)  *Recently started to make poping noise when throttling    I use NGK plugs, and I have a kerker 4 to 1 pipe on it. I have 105 jets in it (I believe). Plugs seem to be correct shade of brown after it runs. Any help as to why it s fouling plugs and or is poping would be appreciated.  

Answer
Hi Jeremy.

What condition are the manifolds in?  Are they tight to the head as well as to the carbs and not cracked?  How about the connections to the airbox from each carb?  Are they all tight as well?
Is the carb synchro due?  How about the valve gap and timing?     The cam chain tensioner could need adjustment in addition to those things.  How about the points?  Are they new or are they due?

Start with that and let me know what happens.

Good luck and ride safe.
FALCON