How do I adjust the idle cam?

Hey everybody I have an urgent question so please if you know the answer let me know. I have a 1987 mighty Max sport 2.6 the carb is stock.
I need to adjust the fast idle cam and I'm having trouble doing so, my manual tells me to set the lever on the highest step of the fast idle cam, which I do, but every time I move the throttle and the lever moves out of the step, the cam moves out of the desired position. I don't know what to do, I looked at my old carb and I noticed the fast idle cam stays in he desired position even if the lever is off the step.
Any advice will be greatly appreciated. Thanks guys (and you gals).
(Edit)...
Would any of you mind telling me how the fast idle cam works? I understand its purpose, I don't understand how it works
mechanically. I don't understand why the cam on my old carb wont move when the lever is lifted off the step, but on the new one the moment I hit the throttle andy the lever lifts on the step of the cam, the cam rotates so when I relieve the throttle and the lever makes cantact with cam, the lever is up past the first step which closes the choke. This is really stressing, I'm out of a car and I only have one. Please help

is it the mikuni solex carb??? cuz my 86 has three screws to adjust the idle...one for the water choke when the engine is cold...one to adjust the idle speed after the engine is warm to compensate for the air conditioning...and one for the vacum advance (: if your just twisting screws and dont know what theyre doing it can get pretty confusing/discouraging

Yeah its a 1987 mikuni, I have the repair manual so being able to locate the correct screws is not a problem for me. Thankfully.
I'm new to Carbs, so I'm second guessing myself on every action I take. hahah I was just wondering what step the lever on the throttle was suppose to be on, on the fast idle cam, when the engine is cold.
Thanks for the reply bud I appreciate it.