Carburettor synchronizer?

[TTM]

Hello,
   
   What does everyone use to tune their Solex carbs on the Bristol engine?
   
   I heard good things about the vintage Motometer unit(s) but I would rather buy something new, and most of the modern "snail"-shaped synchronizers look like they won't be a trivial fit with the Solex inlet flange.
   
   Thanks in advance for your thoughts.

[Jim A]

I used a Uni-syn for years.
   They are still available online for 30 bucks. I think I paid 6 or 7 in 1960.

[Muffin]

I use two methods. The first is with the Crypton Synco Check air flow meter which has a rubber cone for round bell mouth carbs and if you remove the cone there is a flat rubber pad which sits over the intake on the Solexs, they work in any orientation. You get them on 'rip off bay' occasionally which is where I got mine from. The other is to use manometer tubes and not the Bristol way with mercury that you can accidentally have sucked into the engine or with manometer fluid. In motor cycle circles you can get a four (or two) column manometer that uses steel rods. If you drill the spacer below the carbs and fit small brass tubes, then the individual manometer pipes can be connected to each carb, the height the rods rise will tell you which carbs are open more than the other ones. The higher columns will show a greater vacuum hence butterflies need to be opened. Because the rods are all together then you can check that they are also opening together as the throttles are progressively opened. The firm is called Carbtune and are or were based in Belfast, so do a search for them or get the motorcycle comics that come out on Wednesdays. I am just about to balance the carbs on one of my motorcycles after rebuild and they are a godsend. Of course if you have the Weber carbs then the vacuum take offs are already fitted. Both methods are a two minute check now for out of balance butterflies.
   Hope this helps.

[Muffin]

Just checked eBay and there is a Crypton Syncro Check for sale at £75 and loads of the Carbtunes from around £40.

[BE774]

I use a simple piece of hose to listen to the volume of air being ingested by each carb to ensure the butterfly valves are set equally.

[Muffin]

Hmm, I haven't got three ears.

[GSouthee]

I to use the hose method and just listen, you just have to ensure you put the hose in the carb mouth the same distance. you soon learn to hear the difference. I use this on all sorts of carb set ups, su, Solex, Webbers etc.
   My dad taught me, long before all these meters.

[TTM]

Thanks for the helpful replies so far.
   
   

quote:Originally posted by MuffinIf you drill the spacer below the carbs and fit small brass tubes

   
   Upon reading different period documents from Solex it would appear that 32 PBIC carbs feature a vacuum nipple hidden behind a screw plug on the throttle body housing, and that this vacuum nipple should be connected to some vacuum pipe on engines where ignition timing is vacuum-driven.
   
   Could that plug screw be the one just below right of the plug for the main jet hex plug on the picture below? It seems way too small for hiding a nipple of some sort...
   
   
   
   I do not have access to the car right now to check for myself.

[TTM]

I got confused and for some reason assumed that the Solex carbs on the Ace Bristol engine were 32 PBIC when they are in fact 32 PBI-6, which is actually just what's already mentioned in the AC owner manual (I know, RTFM and all that...).
   
   The only difference I could spot between the two is the separate throttle body housing on the PBI-6 mating to the actual body of the carb with a 4 bolt pattern.
   There does not seem to be picture on the Internet of PBI-6 carbs, but this illustration of the 32 BI shows a similar construction, and suggests that the vacuum port should be plugged with a screw plug labeled number 16.
   
   
   
   Looking at the PBI-5 as used on some Jaguars, the vacuum port seems to be left open :
   
   
   
   So what is on your engines, gentlemen?
   
   Are your holes plugged or not? (pun unintended)

[Exowner]

Very interesting. popped out and had a look, and found that -
   Front carb - no plug, but it appears that the hole is blocked further in. Also it appears that there is no thread in the hole for a screw-in plug.
   Middle carb - plugged
   Rear carb - as front
   
   I notice that in the photo above, the hole on the carb on the right is threaded and the one on the left isn't. Though maybe it's badly lit?

[TTM]

Good feedback, thanks.
   
   Solex most likely used a single mould of the throttle body housing and the hole may or may not have been drilled through the port as the housing made its way down the production/supply/logistic line, depending on engine application.
   
   As decades of use saw carbs wearing out and ultimately needing overhauls that in some cases may have required replacing the throttle body housing for any reason, it could be that drilled housings were mixed up with non-drilled ones depending on what carb rebuilders had on the shelf at that moment.
   
   Would be interesting to hear from other owners, to see if we have a trend.
   
   Now to get back on topic, an open side port would be useful to measure vacuum when synchronizing the carbs.

[TTM]

Here is a picture of my center carb. I blew inside the port with a small pipe but as the picture suggests it is definitely plugged. All three carbs are the same. Just thought I would share.
   
   

[Muffin]

I have already mentioned that as the carbs did not have vacuum take offs I fitted brass tubes to the spacer blocks/throttle linkage adaptors. If you use the carb tune manometer set up then you can monitor the vacuums from each carb with out having listen to the hiss individually from each carb. If you have the Bristol work shop manual it shows this set up but with 'U' tubes and mercury columns and caps on each carb - I made some caps and tubes and it was a pain. Problem with using mercury is that if it is inadvertently ingested into the engine it has an affinity to the lead in the main and big end bearings. The other advantage with these manometers is that having balanced the butterfly opening at tick over, then you can observe any difference when setting the idle mixture plus you can check that each butterfly is opening equally as you open the single throttle linkage which is not possible with the ear and tube set up. I dread to think how far out the carbs were on the Cooper S's I had in the sixties having tried that method and checked with the carb tune set up that I now have.
   There is another  Crypton Syncro Check on eBay at less than £20 at the moment.

[TTM]

Hello Muffin,
   
   Yes, I duly took note that the spacer blocks could be drilled to receive proper vacuum ports fittings. However I feel a bit precious with the car and would feel better without drilling anything, unless it is absolutely needed.
   
   What carbs did you have on your Mini?

[Muffin]

I eventually ended up with 11/2" SU's and a 731 cam plus all the other mods.  I was in the Merchant Navy then so could not have it too tuned because my girl friend(wife) at the time used it when away, though I subsequently found out that she would often use all the performance through the gears when frustrated by twonks in Jaguars and MGB's.
   Regarding the vacuum take offs on the spacers, I will take a photo of mine as they are really unobtrusive, if you really are reluctant then I would really go for the Synchro-Check flow meter as it much more accurate than the 'pipe in the ear'. If you want to try out all three systems then you are quite welcome to see them working, I live in South Shropshire.