Was doing a run up with my instructor ,when I put on the carb heat I only get a small RPM drop (25 to 50 at most) ,instructor was worried ,said his Cherokee drops 100 RPM +. Today had a AP mechanic pull the shroud and check the hoses , box and linkage ,all looked ok . Not quite the same system as a Cherokee(heatshroud along muffler) , just a air intake below one exhaust pipe with a screen ,hose and a air box below the carb, just like it shows in the parts catalog. The owner manual and preflight check list does not give a RPM drop number ,just says "check" ???Any other early warrior pilots able to help me know if this is normal ??