rough running on 1st start up of the day

The spark plugs are replaced new every 100 hours. Oil and filter are new at 50 hours. Gas is 99% exclusive Costco premium, every 5 gallon jug tested for ethanol percentage. Airplane is hangared only I have the key. Rubber has been replaced and is monitored at every 50 hr sometimes inbetween. Yes the pressure rises then falls before startup.

Tomorrow I will pull the carbs and open the bowls on an exploratory search.

Update,

Yesterday I took the carb bowl's off and cleaned the idle jet, weighed the floats, (Marvel-Schebler, they never get heavy). There was nothing that caught my eye, everything looked good. Since I was doing a 100hr I had more to do and finished with the top cowl off for the day. I came in today and first thing turned on the fuel pump, the bowl's were empty from the day before. After about 2 minutes I noticed fuel leaving the right carburetor vent line. My vents go into the air cleaner. 

When I pulled the bowl it was full to the top, I removed the float needle valve and could see a indentation in the viton tip. I am sure this is seeping and causing excess fuel to flow into the right intake causing the start up to run rough until it burns the excess off. Probably the engine vibration is enough to seal the needle valve when it is running.

I am positive this is the source of my rough starts. I put new float needle valves in and will retest tomorrow.

Did you measure the brass float armature? This could be the cause. When fuel level is too high then floats should be weighed and the float armature should be measured. It may just need tweaking.

Roger,

On the first disassembly I not only measured the remaining fuel level in the bowls, float weight, and also checked the height of the armature arms.All checked within specs. Since replacing the float needle valve I have run the boost pump extensively, started and stopped the engine many times and flown the plane for 1.5hrs. It is performing perfectly. I am sure it was the float valve seeping.

How old are the carbs or better yet we're they due for an overhaul?