LPG running

[bob hale]

Hello, Happy New Year to all. I have a sleight problem with my LPG car. If I brake a little bit to hard. The engine. Seems to get rich. If I change down and keep the revs up its. Fine. It starts fine on gas and runs very well. By the way. It's a 1956. Rolls Royce Silver Cloud. Thanks. Bob

[Gilbertd]

At that age it won't have a lambda sensor so I'm assuming an open loop system. Three things spring to mind. In cold weather the gas is denser so the mixture will be slightly richer anyway, maybe enough that it isn't noticeable under normal driving conditions but is when the revs drop quickly under hard braking. A quarter turn in on the power valve will cure this (but then it will need turning out again when the weather gets warmer). Going rich at idle is the first indication that the vaporiser is showing it's age, it can probably be adjusted out for the time being but ideally you'll be looking at replacing it in the not too distant. Finally, as it only does it under hard braking, do you have a leak in the vacuum hose to the brake servo?

[bob hale]

Thanks for your answer. It does the same in hot weather. It does not have a servo that works on vac. Its a mechanical one. 1956 Rolls Silvercloud

[Gilbertd]

That leaves a worn out vaporiser then. How old is it?

[rossko]

Has it always done this on gas? "Ram effect" manifests this way on mixer systems. Another possibility is incorrect reducer orientation to line of travel. Both could be ruled out if this is a problem developed after installation (unless there have been changes to air intake, e.g. go-faster filter etc).

[bob hale]

Hello Thanks for that. I have now bought a new reducer. I will let you know how I get on. Thanks bob