There is an option five to consider.

5.) The OS 160 FX comes stock with the main needle valve mounted to the engines backplate, remount the main needle valve to a remote location like the firewall.

Note: Many run the engine in it's stock configuration with good results, however many have complained about tuning problems with their setup, possibly caused by heat and/or vibration of the main needle valve back plate location.
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Schpankme