If the mixture when running on gas is wrong, the petrol system will try to correct the mixture even though you aren't running on petrol. When you do run on petrol, the mixture will be way out until it sorts itself out again. Put it this way. When running on gas all you have done to the petrol system is disconnected the petrol injectors, the ECU doesn't know it isn't doing anything, it thinks it is still controlling the mixture. So, lets say your gas system is running weak. The petrol ECU detects that the engine is running weak so increases the petrol injector pulse durations to try to make the mixture correct again. It adjusts by a bit and it's still weak, so it adjusts a bit more, still weak, give it a bit more and so on. When you switch over to petrol, it is running stupidly rich so won't run right until it learns and adjusts the injector pulse durations back to where they want to be.
Your problem is that you are using a geriatric controller that was designed to operate a separate stepper for idle which you don't have and stream mixers that you don't know are suitable for your engine in the first place. Whatever happens it looks like you are going to have to throw more money at it, whether by paying someone to diagnose the problem (and then replace whatever needs to be replaced) or replace the controller or mixers or maybe both.
Stick with standard plugs, 'special' LPG ones seem to be only special in price.
'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....
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