This time round, some info on the McGee vacuum fuel regulator that came with the grey motor set. The regulator is made from cast aluminium, machined up and fitted with a rubber diaphragm as per below:
- McGee vaccum fuel regulator.JPG (979.42 KiB) Viewed 1825 times
From the numbers given above:
1) Fuel inlet seat assembly. This assembly has been made by soldering a standard Holden Stromberg needle and seat assembly into a brass pipe tee. The seat thread (which screws into the housing) is the funky Stromberg 7/16-24UNS, whilst the pipe assemblies are 7/16-20UNF (with 45º SAE seat angle).
2) Fuel inlet seat assembly o-ring. This is required to seal the fuel inlet seat assembly to the housing.
3) Fuel inlet needle. This is a standard Holden Stromberg needle (in this case Viton tipped).
4) Fuel housing. The housing is tapped to 7/16-24UNS to suit the fuel inlet seat assembly, and 1/8-27NPT to suit the fuel outlet fitting.
5) Fuel outlet fitting. This nipple is threaded to 1/8-27NPT to suit the fuel housing, and 7/16-20UNF (with 45º SAE seat angle) on the pipe end.
6) Housing screws (four off). These are #10-32UNFx7/8” filister head screws, drilled for safety wire.
7) Vacuum diaphragm. The diaphragm has been made from 1/16” thick rubber sheet. The diaphragm shown in the image came with the unit, and was very brittle. I have since replaced it with a new diaphragm cut from a roll of insertion rubber (available from Bunnings).
8 ) Spring carrier. The spring carrier has been made by soldering together a brass tube and disc.
9) Spring. The spring has a free length of 0.62”, a diameter of 0.41” and has been made from 0.044” diameter carbon-steel wire.
10) Spring carrier washer.
11) Vacuum inlet fitting. This nipple is threaded to 1/8-27NPT to suit the fuel housing, and 7/16-20UNF (with 45º SAE seat angle) on the pipe end.
12) Vacuum housing. The housing is tapped to 3/8-24UNF to suit the adjustment screw, and and 1/8-27NPT to suit the two vacuum fittings.
13) Adjustment screw. The screw is a sold metal rod, threaded to 3/8-24UNF. The rod is drilled at one end to receive the spring carrier stem, and machined at the other end to accept a 3/16AF allan key. The allan key is used to hold the adjustment screw whilst the lock nut is tightened.
14) Vacuum port plug
15) Adjustment screw lock nut. This is 3/8-24UNF nylock nut.
The regulator acts to provide additional fuel at idle. Under full throttle conditions, there is precious little engine vacuum. The regulator acts as per the image to the left below.
- Vacuum fuel regulator.png (8.02 KiB) Viewed 1825 times
The fuel (shown in red) is stopped by the needle (shown in pink), which is sitting on it’s seat. The spring (shown in green) provides the force to hold the needle and seat closed. When the engine returns to idle (or cruise), vacuum is generated in the inlet manifold. This vacuum passes to the vacuum fuel regulator, as shown in blue in the image above right. The vacuum acts on the diaphragm (shown in purple), opposing the spring pressure.
As the vacuum increases, the spring pressure is overcome, and the diaphragm flexes downwards. This allows the needle to come off it’s seat, and fuel to flow.
The adjustment screw (shown in yellow) provides compression to the spring. Winding the adjustment screw into the vacuum fuel regulator housing compresses the spring, making the spring generate more force. A larger engine vacuum would be required to get the needle to lift off it’s seat. For a given vehicle, this will delay the introduction of idle fuel (i.e. in returning from WOT to idle, supplementary fuel will be added later).
Like the pump, I'll post some more photos once I get the vacuum fuel regulator screwed back together.
Cheers,
Harv