914 takeoff RPM issue

Hi, im sending an SOS to any 914 guru's out there, I have a 914 that will not make power passed 5400rpm started intermittently and now all the time.

It started lacking power on boost one morning, then came good for a flight and then back to low power. I have just about exhausted my knowledge on this engine.

everything is normal up to full power no hesitation no hiccups just no surge of power when it comes on to boost, 100%v throttle gets me 5200rpm and going to 115% gives me 5400 I have reduced the prop pitch 2 degrees and still the same max RPM, I have been through the carbs, rechecked the fuel bowls are sealing, checked the three way solenoid is working and even bypassed it directly, it makes 40 inches at 115% and EGT's are 760C at full power and same at mid range cruise.

I changed the needle clip to number one position trying to get a higher cruise EGT and reduced the Main jets to 158 trying to get a higher full over EGT to no avail, barely made a difference. Checked the fuel pressure capacity of the pumps, they went to 25psi no problem so plenty of capacity there.

I have not been able to check the ignition pickups due to the tight installation and the exhaust is coming off today to check for any restriction, I suspect an ignition timing issue but am unsure how it could change? The fact that reducing the propeller pitch effectively unloading the engine and it still wont rev over 5400 has me stumped.

Any help would be greatly appreciated.