Echo PAS 280 boggs down

I bought an Echo PAS 280 a while back. It ran great for a short while. Very strong. Then it started bogging down instead of revving up. I carried it to the shop. The mechanic rebuilt the carburetor but very shortly it started doing the same thing again. They then replaced the carburetor. Same thing happened. Ran great for a short period of time then stopped revving up and started bogging down. It has now been to the shop several times. They get it running then it starts acting up. We run several other machines out of the same gas can so gas is not the problem.

Has anybody here had this problem before"