Bristol 411 - Fuel Reserve

[Martin9645]

Good afternoon All,

I have another question for the experts please.

My 411 Mark 1 has a Fuel Reserve button on the dash.

How does it work? I can see a solenoid on top of the tank but no obvious fuel pump ?

Trying to work out if it works rather than running out and then seeing ????

Also do you recomend using a Lead replacement fuel additive. I fuel with 99 RON but have had conflicting opinions

many thanks

[dwomby]

If it works like my 408 seems to, the fuel pump is either the original mechanical at the front of the engine block or will have been replaced by an electric fuel pump elsewhere, usually in the boot area. Regardless, there will be one pump - not a second one for the reserve.

The Reserve switch operates the solenoid on top of the tank. The solenoid switches between two different pipes that descend into the tank. The reserve pipe is longer than the one used normally and so draws fuel from deeper in the tank than the primary pipe can.

I hope this helps.

David

[Sam410]

On the subject of the pipes descending into the fuel tank, these are brass and can suffer from splits or cracks in their brazing which will cause poor running or failure to start if the pipes suck air not fuel.

[peter dowdle]

Over many years I have owned a 401 403 404 408 411 mk2 411 mk5 412
They all have similar systems . Not one of these cars have ever had the reserve system working. Things may have changes but I discovered that the DB 4 to DB6 used the same system as the 411 and reconditioned units were about 800 pounds so needless to say none of my cars including the three I still own have working reserves.A company called Four Ashes Garage would recondition your unit at great cost if the are still about.

Best of luck Peter Dowdle

[David C]

I sent a unit to Four Ashes many months ago but the chap who wound their springs for them either passed away or ceased trading so they are currently unable to repair. Rather a shame as they had got some new bodies made that were ethanol resistant.
I have now decided to fit a Spiyda low fuel level warning circuit instead of having a switched reserve.. This is a tiny circuit board that can be wired in to the terminal board above the battery quite quickly with just 4 wires. Supply plus and minus, sender and fuel lamp. The trigger level is fully adjustable. It requires the incandescent warning light behind the rev counter to be changed for LED as it only supplies up to 20mA but screw in upgrades are readily available. These Spiyda units are currently showing as out of stock but I believe more are being made.
The down side of having a failed reserve unit is that it will draw air from the shorter tube when about 2 1/2 gallons are left so you will only be able to use about 15 and will be hauling around extra you can't use.
Particularly if the car has had long periods of not being used it is worth removing the reserve unit and inspecting the brass gauze. It can either disintegrate or become completely clogged. If the gauze has disappeared it will be straightforward to block the shorter tube and allow you to use all the fuel in the tank.

[Sam410]

My 410 reserve (touch wood) has thus far worked well. I dislike petrol stations so my normal procedure is to wait until the car starts to splutter and then switch to reserve and fill up. My record is over 40 miles on reserve, though I will admit I was getting quite nervous!

[Thomas591]

Talking about the brass tubes..They can be replaced very easily as they are metric 7mm brass tubes with a M7 thread on one end ( of course you have to invest in a M7, but you can get one on eBay for less then 10£).