They don't make carb cleaner like they used to thanks to the gubment-controlled EPA and the green brainwashed idiots. Most is a watered down solution but can still be semi-effective. I have always just used plain old Mineral Spirits. Lacquer Thinner or a 50/50 Mix of Acetone and UTF work well too. If unit is very rusty and dirty, soaking in plain white vinegar for several weeks first is advised. Follow up with few weeks of soaking in the MS. Cleaning internal parts is crucial. Never use drills, reamers, or other objects that can distort orifice diameters. They were originally engineered and drilled at certain diameters for a reason. Pipe cleaners and old used guitar strings is what I use. Once internal halves are cleaned, I use plain old Pine Sol to give a good washing bath. Dry off with compressed air. Let dry our well B4 installing new parts. Get a new TISCO Carb Rebuild Kit; the complete one, not the basic budget one that have no crucial parts. I also advise to use a good wide blade-type device like a chisel to install and remove the Main Needle & Valve Seat. All the jets internal and parts are brass and will booger up screw slot if an improper tool is used. I also advise to use a 3/8 6-PT Deep Well Socket to remove and install the Main Jet.
MARVEL-SCHEBLER CARB INTERNAL DRAWING & PASSAGES SHOWN:
HERE IS A BEFORE & AFTER SAMPLE OF A REALLY BAD CARB REBUILD PROJECT I DID ONCE:
MY M/S CARB REBUILD TOOLKIT:
NEEDLE & VALVE SEAT; ORIGINAL ON TOP, NEW STYLE ON BOTTOM:
TISCO CARB REBUILD KIT FOR ALL N-SERIES MODELS:
Tim Daley (MI)