"With the cart installed at end of the head shell, the VTF is fail to meet the required VTF of 1.5 to 1.9 gram."
I doubt that the cartridge is set to its null points as you've described above. I understand what it is you are trying to do however. There are accessory weights usually available that mount between the headshell and cartridge to solve the balancing problem. You might want to disclose the cartridge you are using and perhaps the community will respond with a vendor for the weight. Then, use the proper setup tools to install the cartridge for correct overhang, etc. Good luck.
I doubt that the cartridge is set to its null points as you've described above. I understand what it is you are trying to do however. There are accessory weights usually available that mount between the headshell and cartridge to solve the balancing problem. You might want to disclose the cartridge you are using and perhaps the community will respond with a vendor for the weight. Then, use the proper setup tools to install the cartridge for correct overhang, etc. Good luck.