Fuel Pump issues

Hi all
new to the site so hi
I have a '93 Classic LSE running on LPG and have a problem starting on petrol which I think is the pump. My LPG tanks are where the petrol tank should be and I have a small petrol tank OS rear next to the LPG tanks. MY question is this, is the petrol pump the same as a normal '93 RR or is it a special unit to fit into the smaller tank?
Thanks in advance for any help you may be able to give.
Spring

it needs to be the correct pump, from the original tank. but cant tell you what you have in the made up tank. i would imagine the lpg people would of done the job properly.
maybe the fuel filter could do with replacing.