75 HP Bristol engine.

[Geoff Dowdle]

To tune the Solex correctly you have to balance the air flow of each carb
, and balance the vacuum on the idle system with in each carb .
If you have a 404/405 Workshop Manual there are details on how to do this .
Most owners use a Holden type air flow balancer and then just screw the
idle mixture screws in or out until the beat of the engine changes then
screw it out about half a turn ,this gets the idle mixtures pretty close.

But the 404/405 manual has detail instructions of how to make your own
triple Manometer , using this the airflow of the three carbs can be adjusted
together (as adjustment of the airflw of one carb can slightly adjust the
air flow of the other two ) . Once the airflows are matched you use the
triple manometer to balance the vacuum at the pilot jets , this is adjusted
by screwing the idle mixture screws in or out .
Then if the carbs are a matched set , jetted correctly and in good condition
you have a chance of tuning the old Solexes correctly .
IT IS WELL WORTHWHILE TAKING THE TIME AND VERY LITTLE MONEY TO MAKE YOUR OWN
TRIPLE MANOMETER.
Every 6 cylinder Bristol owner should have one.

Geoff

In my experience, it is important to assure that there is not an air leak
around the butterfly shafts
of the Solex carburetors.

Bill Watkins

[Geoff Dowdle]

Bill,
I had three 34 ICH Webers(27mm venturi)fitted to my 400 for a few years ,
they made the engine idle perfectly (the throttle shafts have seals to stop
any air leaks), preformed very well once jetted correctly but found it seem
to run lean while crusing on a feathered throttle, until I fitted a
thermostat in the cooling system to bring the water temperature from about
65 - 70 degrees up to 80 - 85 deg , then there were no further problems.
The general performance of the car did not improve greatly by changing from
Solex to Weber , except marginally at higher revs , probably due to the
larger venturis.
The Webers were very very easy to tune at idle , the idle system must be
better designed or made than the Solex .
Although I'm comparing a 55 year old set of Solex in good condition to a
new set of Weber.

Has anyone out there used 27mm ICH Webers I would like to know their
jetting ?

Regards
Geoff

Geoff:
I had 34 ICH carbs on one of my Arnolt Bristols. I can't find a record of the
size of the venturis so the jet sizes that I ran doesn't mean much. However
they were 140 Main, 240 AC & 60 Idle. They worked well for racing, but I can't
vouch for them for street use.

I looked at a chart on:

www.webernorthamerica.com/34_ICH_weber_carb.html -

and saw that it listed 29mm venturis with a range of 130 to 165 Mains
depending on whether the Aux. venturi was 4.5 or 3.5. I suggest that you take a look
there.
Bill

[geo]

Originally Posted by BillWatkins

In my experience, it is important to assure that there is not an air leak
around the butterfly shafts
of the Solex carburetors.

Bill Watkins

I should agree with Bill here and it is something that is so frequently overlooked: on the very-similar carb. fitted to the old two-stroke SAABs (and other old Solexes with which I have dealt) this really can be a problem that upsets the most rigorous tuning attempts, particularly when it comes to balancing multiple carbs.

If it is possible to fit new seals round the spindle (probably did not have one originally, but a suitable one might be found in the SU range if none available for the Solex) and possibly a new spindle (if worn where it makes contact with the body of the carb.), then perfection of balancing will result.

I did not envy a chum who was not getting anywhere fast attempting to balance the eight pots on a relatively modern Lagonda the other day!

George

[Nick Wood]

Hi, while searching for something else, I found this forum discussing the original engine 1065 from my 400/530.

Geoff wondered what was on the ID plate.
I dug the plate out of the burnt out remains and it has the engine number as 400-85-1065 stamped on it.

This may clarify, or further confuse the issue.
Nick