Outdoor Power Equipment and Small Engines - homelite trimmer runs but not smooth

I have this homelite string trimmer that I built out of to homelite trimmers.

st-285bc parts: shaft, trimmer head etc, carb, air filter, muffler

st-185 parts: rest of engine; piston, cylinder, clutch, etc

It ran great all of last summer and up to a couple days ago this year.
I can start it and run it but it sounds like it sputters every few seconds; almost like someone keeps turning the on/off switch on and off. Sometimes it will snap out of it and run fine for a few minutes.
I just changed the spark plug, has gas from last year that had fuel stabilizer.

I have a st 155 That Im haveing some trouble with. Look in gas tank and see if there is junk in there that may be blocking the pickup tube. There should be a little filter on the end also. I took out my filter and hosed it out from the inside out with carb cleaner. I also put new fuel lines on it, only cost about $0.60 and I have about 2 feet left over. I like clear hoses like I have now. Also make sure you have the rite oil mixture and fresh gas can help too. If that doesnt help get a can of carb cleaner and hose it out really good. I like to take carb apart and spray it out.