Stemme 914 F2/S1 low power

I do know an individual who had a mysterious problem on a 914.  It ultimately turned out to be someone had over torqued the bowls on the carbs which bent something that caused an overly rich situation.  The problem was isolated/diagnosed by having a shop install a spare test carburetor.  

The owner told me the the engine ran rough in the mid rpm range and supposedly the bowl was interfering with the high speed jet. --So something you may wish to  check.  I'd take a careful look at the bottom of the bowl.

You did not mention your float-bowl bolt torques. Definitely check those.  I believe it's supposed to be 48 in-lbs.  Too much can distort the bowl and cause problems as Chris described, above.  Too little can mean a bad seal.  If you suspect distortion, you might want to try a pair of new bowls (and new bolts).

I also seem to recall that some float bowl bolts were just a little too long and were thus causing problems with the seal.  I know there's a thread on that somewhere here...

Both float bowls were confirmed to be straight with a flat edge and properly torqued at 48”lbs with new rubber seals added.

This 914 ran fine using paper filters sealing carb bowls before overhaul.  Read that new rubber float bowl seals are thinner and that bolt might need to be trimmed so that 48 in-lbs torque creates air tight seal. Going to check...

guessing you have a manifold pressure gauge , having the same issue on my S12  , installing a MP gauge soon as it  arrives, suspect waste gate stuck open