We have a two story house and all the toilets flush except for the upstairs toilets. They flush but they do not make a full flush.

They do not seem to be blocked, what else can we check

I have one that most repair plumbers miss.. Look down at the bottom of the bowl. If there is a small hole, then that is a jet that starts the syphon action. If it's clogged the water will just swirl around and slowly go down leaving solids behind. Take your finger,(UGH! ) and run it around the inside of the opening. Over the years minerals build up and cut down on the syphon (flush) action. If it is rough or you feel build up, take a table knife and put a bend in it to get around the curve in the bowl and chip and scrap it clear. Next take a coathanger and clear out the holes around the rim. They start the swirling action. And last, check the water level in the tank. It should be 1/2" below the top of the over flow tube. And speaking of the overflow tube, Make sure the small 1/8" tube from the ballcock to the white overflow tube is connected so it discharges in it and that it's flowing when the ballcock fills. This is what raises the water level in the bowl. For a good solid flush they all have to work together. Hope this helps . Tom

Check vents for blockage.also check the small holes on the inside of the rim on the toilets. I have found them to be stopped up from the blue cleaner agent that you put into the toilet tank and cause this problem. I have used a coat hanger or piece of tie wire and cleared the holes. And it sometimes would work, and sometimes the toilet had to be replaced.