sounds carb/fuel related.... When it's bogging try pulling the crank case vent and letting some fuel out, if it picks up and starts running good it's getting to much fuel for some reason.... In the bowl of the drifter carbs there is a o ring around the econojet that could be the issue... or the floats aren't shutting the fuel supply off so it's just dumping gas...
If ur plugs are dry it could be lack of fuel, caused by bad fuel pump, crankcase vent being too loose around the barb (needs a clip to hold the line) or a carb abstruction, or crank seals
There is a small chance it's CDI (ignition) related, buy look closely at that carb first, give er a good clean and inspect! Go get a can of carb cleaner, take the bowl off and go nuts!