You say your sync signal is very small? The 4046 is a high-voltage CMOS which requires its inputs to swing almost the full range from zero to supply voltage. If you are not getting a large sync pulse from your sync fork you need to fix that first. If you areusing the schematic at
http://bs.cyty.com/menschen/e-etzold...BTVmonitor.GIF
Note that the variable resistor in the phototransistor emitter should be 47k (47000) ohms. The "k" may be hard to read.