SOLEX CARBS

[rocketronbish]

Just sorting through some of my accumulated spares and have a number of Solex twin choke carbs. They have all come from 2CV's or Dyane's but some are 26/18 choke and others 24/21 ! and am wondering which is the best to use ? Logic tells me that the 24/21 would probably be better on acceleration but not as quick as the 26/18. Any assistance would be appreciated

[notsmartcar]

I would have thought it would be the other way round on performance Ron

[Ken Hanna]

Ron,
if you work out the total cross-sectional area of the venturis on both types of the Solex 26/35 carburettor, you'll find that the earlier version (21-24) has about 1.7% more than the later one (18-26).
That's hardly likely to make any difference on the road...
.
What it did mean was that the later type could give better fuel economy when cruising on a light throttle, due to better atomisation of the mixture in a primary venturi which was 73% of the CSA of the earlier version.

Ken

[rocketronbish]

Many thanks Ken for your explanation .

[Rodders]

Would any of you clever chaps be able to offer advice on a maddening problem I have with my Dyane engined Lomax? (It's one of your engines, Ron)
It has run perfectly well for over 35 years but suddenly it's started cutting out if the revs drop below 3000 rpm. I've stripped and cleaned the Solex twin choke carb and found a jet appears to be missing! It's the one that would be accessable after removing the screw plug in the fload chamber.
I've also now changed the plugs and suppressors, the coil, the points and condensor, and removed the Boyer Bransden electronic ignition. I've also fitted a new fuel filter - no sign of debris.
I can start it in the garage and tinker about with adjustment screws. It ticks over perfectly. Everything seems fine although a little hesitant until I set off down the road, then after a mile or two it starts cutting out when I take my foot off the throttle. If I blast up a long hill full throttle it's great, then cuts out again when I lift off.
Any ideas? What do you think about the missing jet? Where has it gone? Has the engine eaten it? Was it ever there?
Thanks
Rod (165)

[Ken Hanna]

Rodders,
the primary main jet on an 18-26 version of the Solex 26/35 carburettor has an M4 thread, and is seated deep inside its bore, so is not easily visible.
If it was actually 'missing in action', your fuel consumption would be horrendous, since the bore without a jet installed would be roughly equivalent to a 250 main jet, rather than the original 102.5
https://flic.kr/p/9vX9t1
Ken

[Rodders]

Thanks, Ken. That's just the advice I was hoping for
I better have another look ....

[Rodders]

Sure enough the jet has been in there all along as you said, Ken. My trip to specsavers has paid off!
Nothing else in there to explain my slow running problems though, just one broken throttle return spring.
Thanks again
Rod