What plugs have you fitted to the engine? Must be none resister type .
Check all fuses ,replace if made of white metal for some made of copper .or brass .
Ceck all vacuum pipes , for splits , cracking .
Next check all earth points they will need cleaning and a little greas on the body ,fix them back on..
As for OVP relay look at the fuse or fuses as some did have 2 , remove it and give it a shake .If it makes a noise it shot .replacment or repair it .