Re: freds clone engine problems
I definitely agree on the gaskets, or it could be the head bolts worked their way loose.. which causes the head gasket to leak. Check the torque on the head bolts to ensure they're all still tight and evenly torqued. It's not uncommon for these to work loose as you ride or run a new engine.
Check your fuel filter if it's a fairly new build, junk from inside the tank could clog up a filter enough to allow enough fuel to idle and run, but not make power. This is a problem with the Speed carb if you use the built in shut off valve as it can shed off rubber particles that can block off the needle and seat valve or the main jet... same symtoms, it'll idle and run, but lose power as the rpm's go up. the biggest problem if it's the shut off valve shedding off rubber particles is that the valve is after the fuel filter so the filter can't protect the carb from it.
Other things to look at are check for a loose spark plug in the head, loose head bolts, loose intake bolts, and all gaskets and crank seals for leaking like mentioned above. A bad magneto coil can also cause sputtering and hesitation before it fails completely as well.