It really depends on the type of polymer. B-12 is inert to some plastics like polyethylene and nylon but devastating to others like ABS and polycarbonate. Do you know what kind of plastic(s) you would be soaking?

Thanks for your response. I'm overhauling a 12-year old carb. The choke plate is metal but the shaft is made of black plastic. My basic question is whether or not I can safely soak the carb body in undiluted B-12 Chemtool Fuel Treatment. Was B-12 Chemtool Fuel Treatment formulated to be used for this purpose?

A good rule of thumb is that any parts exposed to gasoline in their normal operation will stand up at least briefly to concentrated B-12 Chemtool Fuel Treatment (part #0116). If you want to test it first, put some on a Q-tip and run it across the plastic shaft to see if it “fogs” up. However, the fuel treatment was not meant for soaking parts in due it’s extreme flammability and fast evaporation rate. Instead, our Chem-Dip products (parts #0996 and #0905) are better suited for such applications. You also might be able to get away with cleaning the choke plate and shaft using our spray cleaner B-12 Chemtool Carburetor, Choke & Throttle Body Cleaner (parts #0117 and #0120). They are aggressive enough to quickly cut through any fuel residue and carbon build-up but also evaporate fast to minimize contact time and possible damage to plastic and rubber parts, seals, etc.