I have a shindaiwa weed wacker that when you pull the trigger it bogs down just for a second then it will pick up rpm's and the hotter it gets the faster it will run. There are new seals top and bottom / new carb / new gas lines and I removed the screen on the muffler, But it still does not run the way it should . Can anyone help me with this problem.thank's Ron

Hi,
Sounds like it has an air leak. Get some aerosol like carb cleaner, brake cleaner, WD40, etc. and try spraying it on the running engine to try and determine the location. This will not tell you if it is one of the crank seals, but you can get to most every other place.
Peace,
Clarke