403 Sparking plugs

[Geoff Dowdle]

Graham
Although the carbs have been rebuilt by a specialist , the only way to check the float level is at 16mm down from the top of the main carby body ,is by an external sight tube with the engine running .

Geoff

[GrahamH]

Thanks. Given the history of flooding and the fact that petrol consumption is high at 15 - 18mpg I will certainly look at the float levels. Previously mixture has only been checked by gas analyser on idle.
I recall an article in the Bulletin some time ago, I think by Alan Blackwood, where the art of checking the float chamber levels by external tube was described in detail. Unfortunately I cannot find my copy of the relevant Bulletin.
Geoff, can you or other members point me in the right direction or recall the bulletin number?

[Geoff Dowdle]

Graham,
15 - 18 mpg is not very impressive , most 6 cylinder Bristols should achieve 26 - 30 mpg on a steady trip at 70 mph and about 20 in city driving .

Attached is a simple float level sight tube similar to what I use .
It is made by drilling a hole in the centre of the hex of the main jet holder. Then solder a small piece of copper tube into it .

I suggest you check the diameters of the main & idle/pilot jet to see if an earlier owner has drilled them out . this was a common practice in the past.

I have found the best way to check the mixture is with the use of a mobile gas analyser, it can give the mixtures right through the rev range under various conditions .

Geoff

[GrahamH]

Thanks again, both for advice and photograph.

Will take on board and get the float levels sorted, along with the fuel consumption and the plug fouling. May take me a little while but will report back.