The description by mrfixit is spot on - exactly as we have on our one, with the exception that it has never had a dual fuel set-up, even though it has a carb. I do not know its full history, but it looks to have been factory converted from new. All the gasolene connections etc. are blanked off and there looks to have never been a tank and fuel line. It used to run perfectly with its previous owner, who then started to have this problem. We took it over - thought it would be a simple problem to cure, but is proving more difficult. At the moment have the lpg feed connected straight into the solenoid on the top of the Impco, bypassing old pipes and filter, and are now looking at the bottom solenoid valve to again check its operation - if this is working OK we can see no reason why at least it should not idle properly.