404-5 carb jetting differences

[Julian Caples]

Yes emulsion tubes are available - 10s are no problem the others are a bit harder - Classic carbs (classiccarbs.co.uk) have had them, classic carbs here in oz have 10s (classiccarbs.com.au) as do Rocky SRL in Italy (ebay store)

I'd have a chat to Tony Byford before mucking around - he's very good

Yes a rolling road is the way to go

Not withstanding my comments about the idiosyncratic parts bin approach, if the car was otherwise running well, then the spitting back may well be something simple and amenable to tuning - particularly check the throttle linkages - if one carb is not opening at the same rate as the other two you can get spitting back

Julian

[Geoff Dowdle]

Glenn,
You have mentioned all the jetting sizes but what are the venturi sizes.
403 - 406 have 26mm ID
Most Bristol Sports engines , C,D,D2 have 28mm or 27mm
The size of the venturi determine the size of all other jets, then compression and other factors have a bearing as well.
The pilot jets #44 seem too small to me.
I have found over the years that many jets have been drilled out but they don't necessarily flow at the same rate as expected.
Do you have an inline filter between pump and carburettors as small particles can block or partially block the pilot jets.
Are the throttle bases all the same , most Bristols have two progression ports but other bases from Standard Vanguard, Landrover, Jaguar etc mostly have 3 or 4 progression ports .
Have the float levels been accurately checked, I have found an external sight tube from the main jet holder is the only way to do it accurately. Replacement carburettor tops are often machined differently where the needle valve is fitted, for different applications . Fitting a new needle valve with the standard 1mm washer can give quite different float levels depending the machining of the top.
I suggest you start the tuning process with three #10 emulsion tubes and have each carburettor jetted the same.
The emulsion tube holders can be different lengths which can raise the emulsion tube in relation to the float level , check the heights of the emulsion tube holders above the top of the main carburettor body, that they are all the same.
Remember you most likely have 70 year old carburettors that have been through many owners and so called "Carby Specialists" who have modified and exchanged parts from other carburettors which might not match the original part.
It might all sound a bit depressing but this is the accumulation of problems I have found in the past trying to get three Solex running together correctly, but on the other hand an original matched set in good condition mostly work very well and are easily tuned.

When you are happy you have a matched set in good condition take the car for a rolling road session to check the mixture through the rev range under load and calculate the ideal distributor advance curve needed. Then build that curve into the distributor .

Geoff

[David C]

I just had a look in my spares for 405 and 406 emulsion tubes.
I have what look like L29 with 3 holes and DL with 4 holes and a bit shorter than the L29

Neither of these seem to go with the numbers below and I think they came off carbs on stock engines.

Any clues?

[GlennBurnage]

'Carburettor Hospital - Specialists in carburettors and spares'
contact details via the web. They had all I needed to get my carbs similarly jetted. How it all goes will follow!

Geoff, many thanks, will let you know the progress

[GlennBurnage]

Having got all excited about finding parts to get all 3 carbs set up equally, I find that there are differences in emusion tube diameters!! The ones supplied by the Carburettor Hospital were 4mm diameter and the ones in both cars that I have with 32bi carbs are 3.5mm diameter. INRacing have some of the right size on their way to me. Why I didn't try them first is a mystery to me as they have sorted out several carb related problems in the past and are always very helpful (and expensive, which I'm happy with).
One lives and learns -aparently!!!