This is called "bogging", so you can know what to google. It feels like fuel delivery but can be electrical. Check your spark plugs to see if they (it) are (is) fouled. Replace it.

Then drain all your gas and replace it. Water in the gas can cause this as well.

This is called "bogging", so you can know what to google. It feels like fuel delivery but can be electrical. Check your spark plugs to see if they (it) are (is) fouled. Replace it.

Then drain all your gas and replace it. Water in the gas can cause this as well. If you have begun to store it outside, you may want to move it inside.

Also, timing could be a factor.