Carb kits are quite straightforward to install and a good system to fit if you have not had any experience in LPG.
Once you had fitted the rear end system you should have a 6mm pipe up to the engine bay.
The first thing to fit to this is the liquid filter/shut off valve. It is advisable to make a coil in the pipe before fitting it to the shut off valve, this will help take any stress off the joint. Fit a second coil in the pipe between the shut off valve and the vaporiser/reducer.
Mount the vaporiser to the inner wing or other suitable position. The vaporiser needs to be fitted upright in the same orientation as the road wheels. In other words facing the engine rather than the front or rear of the vehicle. The reason for this is because the diapham inside that controls the flow of gas, is very sensitive so it is possible that hard acceleration or braking could cause the diapham to move, thereby disturbing the mixture.
There are three other pipes to fit to the vaporiser, two of these are water pipes, these need to be fitted into the heater pipes. You can normally find these at the vehicles bulk head. But be careful that they have a direct feed from the engine without any control valves interrupting the flow of water. It is important to fit a 'T piece' into both of the heater hoses and to run two pipes to the vaporiser. This will ensure a good flow of water under all conditions.
The third pipe runs from the vaporiser to the mixer on the engine. The mixer/s must be fitted to the outside of the carb/s. All of the air entering the engine must travel through the mixer/s before entering the engine. The mixer/s have a venturi, which speeds the air up as it passes through it. The increase in air speed then drops away as the mixer increases in size. This venturi causes a depression or suction on the pipe from the vaporiser which pulls on the diaphram and releases more gas. The more air that enters the engine the more gas is pulled in.
Fitted between the vaporiser and the mixer is a hand valve, known as a power valve, this helps to achieve the correct mixture. It works by restricting the pipe which in turn restricts the flow of gas and also reduces the pull on the diaphram.
Fit the petrol solenoid valve into the petrol fuel line close to the carb. The closer this is to the carb, the quicker the change over from petrol to gas can be performed. Check the fuel line for a mechanical lift pump. If there is one present, fit the petrol solenoid on the carb side of it. This will allow the lift pump to stay full of petrol. If it is allowed to run dry it can damage the diaphram which is inside it
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Fit the changeover switch in a suitable position in the cab. When deciding where to place it consider how easy it will be to use. (I once converted a Discovery for a chap who only had one arm, I fitted the switch to the left side of the steering wheel, he only had a right arm! I moved it for him of course!)
The type of carb switch I use is either a VIP appletec or AEB 722, these are both good quality switches that stand the test of time. A Range Rover I converted 8 years ago still runs on the original VIP switch that I fitted.
Generally the wires are connected as follows:-
Red 12volt ignition fed live
Ensure this is a good connection to a good feed, do not use the ignition coil+ as this can cause problems due to low voltage/amps.
Black negative/earth
I always connect the earth to the negative side of the battery. This means you are sure of a good connection and you always know where to find it should you have any problems in the future.
Blue
This is the power to the LPG system, it needs to be connected to all of the solenoids, the tank/s, shut off filter valve and vaporiser.
Brown
This needs a signal from the negative (-) side of the coil, so that the switch knows when the engine is running. If it loses this signal, if the engine stalls etc, the switch will shut down the system.
Yellow
This wire needs to be connected to the + of the petrol solenoid. it will power the petrol valve when the switch is put into the petrol position, allowing the petrol to run to the carb. This valve will also require a good earth.
Green wire and white wire
The green wire is connected the the level sender signal wire. Check which type of sender you have.The most common types to be used are either a hall effect sensor which has three wires, black which is earth (-), red which is live (+) this can be connected to either an ignition fed live or the blue wire of the LPG system. Green, which connects to the green wire of the switch.
0-90 ohm This sensor only has two wires, a black which is earth (-) and white which connects to both the green and the white of the switch. (not all switches will have a white wire).
10-50 ohm or AEB. This type of sensor also has only two wires. A Black, connect to earth (-) and a white which connects to the white wire of the switch but not the green. On this type of sensor the green wire is not used.
Level sender wirring chart
| Black | White | Red |
| 0-90 | earth | green | |
| 10-50 | earth | white | |
| hall effect | earth | green from sender to green from switch | ign live or blue wire |
As I said on the previous page I always fit a Lambda control system to any carb engine that I convert.
This is done by retro fitting a 'Lambda probe' or 'oxygen sensor' into the exhaust and a control box/stepper motor to the LPG system. See Lambda control setup for more details
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Common problems
Clicking or buzzing from the changeover switch,
This is normally down to a bad earth on the black wire or a component. I normally run all the earths of the system to the battery negative. It can also be caused by a weak ignition fed live.
Switch lights up and cuts petrol but does not allow gas to flow.
No signal on the brown wire, check that it is connected to the negative of the coil. Or try wrapping it ten times around the HT lead (from the coil to the distributor)
Not enough gas flowing to run the engine properly.
Vaporiser needs adjusting (see vaporisers) Power valve shut, open valve. Air leaks on the engine or mixer/s, check all air pipes on the carb/s and inlet manifold, check brake servo pipe, distributor advance-retard pipe. Check gas vapour pipe from vaporiser to mixer for tight bends and restrictions.
Sometimes spraying easy start with the engine on idle will show where air leaks are, the revs will increase when the easystart is sucked into the engine.
As with all lpg conversions it is important to check that the electrical system of the vehicle is in good condition, if you are in any doubt, replace spark plugs, distributor cap, rotor arm and HT/plug leads.
An example of mixer plates
Standard Power Valve Y Power valve for use Typical 4 wire stepper motor
with twin carbs / throttle body for use with lambda control
systems
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