Su Carburetor Balancing Tool
The instructions for the SU tunig kit suggest you should use a Unisys along with the wires. The synchronizing of two or more carburetors should be done prior to the final mixture adjustment. For precision synchronizing, a 'Unisyn' should be used along with the tuningtool. Since the pistons are lifted equally by the air flow, it is possible to synchronize without flow meter by comparing the height at which each piston is lifted at idling and at higher R.P.M. The synchronizing at idle speed should be checked by pressing the pistons down for a very short moment (one at a time). The pointers will help to compare the level to which the pistons are lifted. Ifa piston is lifted higher, this indicates that this carburetor has a higher air flow.
SU Carburettor Tool. This SU carburettor tuning tool for balancing twin and triple carburettors is available from the MG Owners Club (MGOC) at the following link: SU Tool. More Su Carburetor Balancing Tool videos.
The throttle stop screw for idle speed or the by pass (on some carburetors) must be adjusted until the air flow is equal on all carburetors. Accelerate several times and compare the movement of the pistons to detect a - stickylin!-'-ageor throttle shaft and tocheck the synchronization at higherR.P.M. Steve D '70B - current status. Using tool to test mixture: 1 carb air flows adj perfectly,eng running at idle. 2 Tool wires exact same ht,one behind other,back carb wire behind wire for front carb. ( note,wire thickness/diameter is 5/64 inch) 3 grab aluminum tubing on one carb and lift so wire is about 1/32 above other wire.
(substitute for old technique of lifting pin/piston method) Should have slight /temp rpm rize if mix correct at idle speed Do to both carbs!! 4 Run engine at 3000 rpm,Do same test for both carbs, should have no change in rpm. Note if easily noticable changeWORN needle probable.
Spridgets manufactured up untill 1975 typically came with twin SU carburettors. As with any muticarb setup, it is necessary to balence them. There are tons of devices and methods out there but most of them are designed with motorcycles in mind. Theoretically, the vents on vented SU HS2 and HS4 carbs offer the possibility of using some kind of vacuum guage to balence the carburettors, however considering the simpler and less expensive options out there, the following methods are preferred. Exparimental methods that take advantage of the vents will be discussed in a separite article. First of all is the simplest and least expensive (yet not the least effective). All you need is a length of aquarium tubing.
Place one end in your ear and the other end just under the piston in your SU carb (as shown). Then try to make the hiss from each carb have the same pitch and volume. This also has the andvantage of taking up the least space in the toolbox. Next are two balencers that are commercially availible. They are reletively inexpensive and easy to use. They both work much the same way in that the airflow into the carburettor pushes agaisnt a vane inside that indicates how much air is going into that carb.
I like that they are very easy to read, but they aren't as sensitive as the human ear. On the left is a Carburettor Synchronizer manufactured by EMPI.
It is sold from by a variety of distributors including Moss Motors USA (part number 375-321). It presumably works the same as the one on the right, but it has the advantage of the cone shaped adapters which might be easier to use (though I haven't actually had the opportunity to try it out).
Above right is a unit produced by Schleyer. I bought an old one at swap meet for $0.50. The only thing wrong with it was some rust, cobwebs, and the fact that the needle was stuck behind the stop.
After a little cleaning and servicing (not difficult), it worked fine. Mine was missing the adapter shown in the picture, but a fresh roll of electrical tape did the job nicely. It is currently available from JC Whitney (SKU number 1JA 882792), and costs $39.99. I cant be sure but it is possible that this is the same Schleyer as the Phillip Schleyer, featured in this next ad for a rather intriguing device used for synching SU carbs specifically. It too appeared in the February 1962 issue of Car and Driver. It also appeared without the pictures as a classified ad in Popular Mechanics in March of that year.
Presumably this works by measuring the height of the piston in the vacuum chamber. Carbs, the piston automatically rises and falls to adjust the size of the venturi and the mixture depending upon throttle and load conditions. On some versions of these carbs there is a small vent hole in the dashpot cap. It may be possible to insert some straight sticks marked with some tickmarks showing where the piston is when the engine isn't running and then you might be able to visually compare how far these sticks move when the engine is idling, revving up, slowing down, etc. I would love to see one of these Schleyer units in person.
It might well be the same as the S.U. Tool kit currently sold by Moss Motors as part number 386-300. Picture below. The next link is to a thread on the MG Experience forum about this toolkit Instructions can be found on the following link Next are two tools that are no longer in prodoction. Both of which show up in SU tuning manuals.
First is the Crypton Sychro Check. Its featured in the 1975 edition of the on pages 336 and 345. Presumably measures airflow just like the EMPI and the Schleyer. They do turn up from time to time on auction sites. The following pictures are of one that turned up on hamilton.canadianlisted.com. Then there is this enigmatic device thats also found in the, this time on page 349 in a section on HIF carbs on MGBs (why this is in a sprite/midget manual I'll never understand). Anyway its an interesting tool that measures both carbs at once and looks like it gould be a great tool to use.
Tire Balancing Tools
Unfortunately the manual doenst give a name or patent info on this device so tracking down an example is quite difficult. If anyone has any info on it please let me know. Finally, is my least favorite balencer. This is one device which is probibly better suited to larger engines. Its just not sensitive enough to measure airflow into this tiny engine.
Its true that you can calibrate it but to do so means you have to nearly screw the adjuster all the way shut, therby nearly blocking off the carb you are measuring and possibly even stalling the engine. It is is the venerable Uni-Syn. This device has been manufactured by a number of firms including Royze, Motometer, and Edelbrock. They have been in production as early as 1962. Here is an ad for this device as it appeared in Car and Driver in February 1962, and pictures of an actual unit made about that time.
This unit features a tube with a lightweight plastic float in it. The unit is placed flat against the inlet of the carb and the wheel adjusted to increase the vacuum in the tube until the float rises.
You then compare how high it rises on the first carb to how high it rises on the second carb. It may also be possible to adjust it by altering the angle of the tube. I may need to experiment more, but I would guess it works better with bigger engines. Anyway, Moss sells this unit for about $34 and it's part number 386-200.