There is no altitude jet on a series F carb, so there is no adjustment. If your are talking about the jet on the left side of the carb, under the sticker, that is the idle jet, which is fixed, but will plug easily if fuel is left in the carb for an extended period of time.
#5
Russ2251
See parts explosion in post 3.
(Part #4 indicated)
I pretty sure OP would not be referring to non existent screw.
Hey Russ, Lawn Boy had three different carbs in the F series. F100, F200, F300. The model you show is a model F300, which was not used as often as the other two. The other models had them on the side and were much more popular. What you are pointing out is an adjustable needle, not an altitude adjustment. There is a difference if you understand how carbs work and as you can see in the attached. You probably have that already, but others can see the difference. The OP never gave us the exact carb he had, so I picked the most popular. If you want to call me out, make sure you can back up your claims. I gave the best answer possible with the info we were given.
Here you go, this is the link to adjustment of the carbs for the F series engines from 1978 through 1988. It's the later F series Lawnboys that have the plastic, non adjustable carbs (around 1995 and on). Sometime between 1986 and 94 was the Walbro era of F series carbs, the best of them all in my opinion, they are adjustable and being metal they don't warp like the plastics do. Altitude jet versus altitude needle? Makes no difference to me.