Surly

Make a V-tune run that gets more data around your trouble area. You need to get the surrounding cells with good data then take a look for knock retard by recording a DataMaster file. Go to the "Help" file for DataMaster and it will show you what to do. You should get the V-tune done with good data showing in the cells within your problem area, then adjust the spark then go back and V-tune again. It could be a problem with a lot of things but you need to start by getting the engine in a proper state of tune first.