cimmarron toilet flush capacity

I have several Cimmarron toilets installed in a house that I have recently remodeled and added onto. I am having a problem with the some of the drains connected to the toilets backing up. Only the old existing cast iron drains are backing up, no problem with the PVC. I never had a problem with these drains when we were using the older higher flush capacity toilets. My guess is that I am not getting enough water with the solids to insure everything flows out.

I pulled the tank covers off the tanks and noticed that when the toilet flushes it only uses a portion of the water in the tank. Kohler confirmed that this is correct, that the extra water is to increase the pressure. I measured how much water is leaving the tank each flush and got about 2.5" or .86 gallons, roughly half the 1.6 gallons it is set at. Does anyone know if this is correct? I've adjusted the chain tension per Kohlers recomendations but it doesn't seem to change how much water leaves the tank.

While I could hold the lever down and use the entire tank capacity I cannot rely on this method when I have guests use the toilets. Any ideas?

Some of the toilets are very sensitive to having the proper flapper valve. Have you changed yours to a generic replacement? SOme of them are adjustable. Sounds like you may need to look into that. Some toilets just have horrible flushing, don't know about that model; you might want to check the report on this site's main page to see if it is covered.