Small Engines (Lawn Mowers, etc.): Echo 400elv Chainsaw surging at high run, mixture adjustments, air leaks

Question
We have been trying to find a problem in this chainsaw for months.  We found a baffle that had broken loose in the exhaust, blocking the exhaust outlet on occasion.  but even with this removed it is still "surging" very badly at high run.  We have also tried mixture adjustments and pulled the carbie down and cleaned and checked it. The fuel filter is clean and the piping isnt blocked.  We havent found any airleaks. Any ideas?

Answer
Hi Adrian,

The surging may be caused by intermittant fuel or air flow in the carb.  I would try adding a new diaphram or replacing the carb.  
Air leaks at the crankcase seals would cause a lean condition.  
Other than that, I can't think of anything else.

Good luck and keep me posted.
Michael