Chemtool is excellent and one of two products I use, the other is a high PEA cleaner like Redline SI-1, Techron, Gumout AIO.
There are two types of fuel system and injector contaminates that can be helped with these products and some that nothing will help. The ones you cannot do anything with are sand or similar that got into the system (more common on small marine stuff) and incinerated nylon fuel filters in the injectors (DI injectors).
The two you can do something about are varnish and hard carbon deposits, varnish is common in all engines including carbs and especially small engine OPE, this is where Chemtool really shines,it will remove varnish deposits almost on contact. Using a splash of Chemtool in OPE tanks a few times a year and before storage will prevent carb issues almost indefinitely.
My Lawnmower and snowblower are both 14 years old and still have the original carbs and have never been cleaned or adjusted, both start first pull and run perfectly. The Chemtool really works well but it does not do as well on hard carbon heat formed deposits commonly seen on the business end of the injectors. For this type of deposit PEA based cleaners do the best job.
The PEA cleaners are not great on varnish, their effectiveness is minimal compared to Chemtool, from my experience the most effective to maintain the whole system cleanliness is to use both types of cleaner alternating them for a few tanks. OPE and other engines with carbs are not subjected to the kind of high temp deposits found in injected engines so Chemtool is all that is required.
