Does the prop go past 2200 as you apply full power on ze takeoff run then settle down back to 2200? If so it could be a crack within the crankshaft. I've had the problem twice in the past. If there is a crack then too much oil could be pissing into the crankshaft and would give you a problem with RPM or on the other hand it could be a dodgy gauge. Get that checked first and monitor your oil consumption.
Sometimes these things can be the simplest of problems. Long live the 206............