87 honda accord idles rough
 

i have an 87 accord carb. engine. when i first start
it up it runs fine but after it runs a little while it starts to idle
rough. it will rev up to 1200 rom's then drop down till it almost cuts
off then it will rev up to 1200 rpm's again. it will do that a few
minutes then cut off. it will start back up fine and then it might do
it again or it might idle ok thanks