Which LPG mixer? 1963 1098 saloon on SU carb

[bigwheels]

Yes I was thinking the same but as it likes to click with the ignition on and the engine not running on so it will probably still click when driving around. But I think its only maintaining a bit of pressure in the fuel line to the float chamber.

I'm just studying cop 11 for the LPG installers regulations as I want the installation to be able to be certified so I am sticking to the regs like glue. I have got the mixer and filed it down 2.5mm each side and it fits but there is more filing to do as the carb has a little air hole which is now obscured by the mixer in part.

There is a lot of thinking to do before I start, but I suppose its just formulation of a master plan!

[bmcecosse]

I assume the 'mixer' goes on the front of the carb - between air filter and carb.....?

[estwdjhn]

I'm still mystified how the flow of gas is regulated to match the air flow? Does it work on throttle position - or inlet manifold vacuum? Obviously on modern cars with ECU etc - it's all done very accurately via the electronics and the Lambda sensor - but on a carb car??

Several options on this.

There are essentially three ways to control LPG feed to an engine.

1) Venturi effect from carb inlet.

This is the most common system for older engines. Anything which has a mixer plate bolted to the carb probably works this way. Basically, LPG is taken to more or less atmospheric pressure by the vaporiser, then fed via a restrictor valve to the mixer. The more throttle the car is given, the more intake air is drawn, the more intake air is drawn, the more gas is sucked from the mixer plate. Cheap and nasty systems have a fixed restrictor valve(set on installation), this means the mixture tends to be wrong over at least some parts of the rev range. Better systems use a lamba sensor and feedback system to adjust the restrictor valve and keep the mixture something like.

2) Gas Carburettor

Not very common for some reason, apart from on forklifts. Mainly they use a suction driven float (like an SU carb) to open or close the gas control valve (usually gas is fed from the vaporiser at just over atmospheric pressure). If set up properly, a good gas carb gives a decent mixture control over the whole rev range. Usually they are mounted in the intake pipework, just ahead of the petrol carb, and they rely on the petrol carb's throttle spindle for engine control. Two main systems I've encountered, Impco CA100 series (mainly found on forklifts, I had the setup on a 2.6L landrover six cylinder for a bit, but found it was too restrictive for that size of engine), and the Polish BLOS carbs (superb bits of kit, would strongly recommend to anyone).

3) Efi

Mainly used on modern cars with existing petrol Efi, but it's perfectly possible to retrofit on a carbed engine, if you've got a mind for that sort of thing, and a few quid. Use a timing and Efi controler like a megasquirt unit, and with relatively few sensor inputs you can have a 21st century A series of your very own. I still want to build an LPG only efi setup on my 2.6 landrover engine at some point, but it's unlikely I'll ever have the combination of time and money required (I reckon the bits I would want for full sequential multipoint injection, and controller to match would be around £1k - a budget monopoint systems could probably be <£500).

[bmcecosse]

Yes - thanks - my LPG Cavalier had the 'venturi' effect system. I suspect that's the way with most carb engines . I also suspect this is why they ask for the engine to be started on petrol - and then turned over to gas...to reduce the risk of gas leaking from the mixer plate when the carb is not 'sucking' - also to try to get some warmish water through the evaporator perhaps!