if you do set all the dwell and timing where it should be that like mbshop sayes and it still does it it deffenetely could be the throutle body switch.Mark it and try and move it either way and test drive.
And Ralph yes you are paretly right about the points,but you have to be very accurate on adjusting them.Sometimes i could not read the dwell on the anylaiser i did the points adjustement from only the fieler guage.But you know how it is when dwell is out than the timming is out.
Harald