HMMMMMMM
Dual throat Nikki carb. I've seen the o-rings inside those Nikki carbs cause that engine speed changes.
I did not say that carb is your engines issue but it's a good suspect.
Here is a link to review about your 796997 Nikki carb. (repairs, etc)
outdoorpowerinfo.com
Here is some info I have saved from my files about those type carbs FOR YOUR REVIEW.
Nikki dual throat carb repair/rebuilding links
Nikki dual throat carb tips and re-building LINK.
Guy asks about jets sizing and re-building a dual throat Nikki carb
https://www.lawnmowerforum.com/threads/nikki-dual-carb-main-jets.29187/
You tube video part 1: (newer style aluminum float bowl Nikki
) USE KIT 54832 @ $7
part 2
(older model with steel float bowl) USE KIT 54833 or 54834 @ $9 each depending on the style of Nikki. See part 2 of the video to determine which kit needed.
Nikki dual throat carb repair/rebuilding links
Nikki dual throat carb tips and re-building LINK.
Guy asks about jets sizing and re-building a dual throat Nikki carb
https://www.lawnmowerforum.com/threads/nikki-dual-carb-main-jets.29187/
You tube video part 1: (newer style aluminum float bowl Nikki
) USE KIT 54832 @ $7
part 2
(older model with steel float bowl) USE KIT 54833 or 54834 @ $9 each depending on the style of Nikki. See part 2 of the video to determine which kit needed.