can someone please help me?

i have a 89 mazda b2200 with a completly stock 2.2 engine that is carbed. the problom im having is that once it warms up and it idles where it suppose to it cycles so to say. it will idle for like 10 sec at like 700 rpms and then it will jump to like 1200 rpms for 10 sec. i cant figure it out. other then that it runs ok. if u need anymre info let me know. any Help is greatly appreciated. thanx

is the A/C on? it could be the engine compensating for the strain of the A/C pump? Is it warm out? When there is no airflow moving across the radiator(such as when ur driving) the fan kicks on, and if its a mechanical fan, the engine turns it, so the engine pushes harder to power the fan. If check those.... Try turnin the AC off and see if it does it, if it still does, open the hood, and see if the fan is kickin on/off with the RPM jump.