I had two of the MC barrels get tight after about 2 gallons of fuel on my 1.60's. This was something that did not happen with my 1.45's last year.
If the MC barrel is sticking, it is nearly impossible to tell until you see it acting up on the ground with the engine off. The symptoms I experienced were that it could quit at any throttle movement, opening or closing from any throttle position.

Here is what worked for me.
I switched from a cable pushrod to a .050 steel rod. (you could try smaller diameter, this is something I had on hand)
My servo is a small JR 341, so I maximized leverage by going to the inside hole on the servo. Being careful to maintain enough throw for the MC barrel.
This next part can be touchy so be careful if you try it. Disassemble the carb and remove the MC barrel. Take off the small o-ring and find a small file that fits the groove where the o-ring came from. Chuck the barrel in a drill press and turn it at a very slow speed. Just barely touch the file in the groove a time or two to make the grove .003 of an inch deeper. Clean it up good and put the o-ring back on and put the carb back together. If the o-ring is at all damaged, replace it. It should now move very free now and even easier after flying.

As I said, it is a delicate process that I am sure would void any warranty.

The only time mine quits now is when I run it out of fuel. It has been very reliable and smooth for hundreds of flights since the change.