I just started having a problem with my engine that I have not experienced before and was wondering if anybody had any suggestions for the 1st place I should look for the solution. I have a thunder tiger 46 pro running 10% nitro 18% synthetic/caster blend (same fuel whole time). I started the day (as all other days) and the engine ran fine, good idle great transition and good top end. I had it set just audibly below peak rpm, the pinch test increased rpm substantially. I have the three line setup in the tank, (intake with clunk, exhaust pressure with clunk and plugged vent for fueling). The tank is visible and not foaming. The transition was almost instantaneously from low to high rpm (fast reving). After about 4 - 9 minute flights, I thought the engine started to run a little lean during flight so I brought it down to richen it up but found out that the transition was very slow. From low throttle to high throttle the engine does not rev very fast. It takes about 5 – 10 seconds to reach full rpm but is smooth and not burbling. The idle is still good and the top end is still there, just takes a while to get there. It is like the throttle is being pushed slowly but it is not, the servo moves the barrel wide open very fast. At the field, I took out the high speed needle and blew air through the barrel and air came out the needle hole.

What do you all have for the diagnosis?
Thanks for any replies.