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SU balancing on BJ8's

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AndrewMawson

Jedi Trainee
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Using a conventional air flow balancer or 'ear tube' is a pain on the BJ8 SU's as the air filters and hence choke mounts have to come off, and the filter bolts really need the float chamber lids off to get at. It all gets a bit tight round there!

There used to be a gizmo comprising a thin walled aluminium tube and some bent bits of wire that let you effectively measure the rise of the piston assembly in each carb and set things to get them the same.

Has anyone used this method and found it reliable and know a UK source of the kit ? (found one Stateside : https://tinyurl.com/3gexm ) If all else fails
I'll get some tube and start bending wires <g>
 
I have both the Moss type of Unysin and the wire job. As you stated it is much easier to use the wires. Also it has the advantage of being able to lift the pistons to check richness. Simple to use. It simply lets you see how high each piston goes up and compare them. No moving parts or openings to get clogged. I leave them in the car cause they don't take up any room and they cannot break. The tubes have the added advantage of being the right sizes (by design) for adjusting the float forks.
 
Try a set of airline earphones (the hollow tube type).
How you get them is up to you. But you get stereo as opposed to a single hose. I balance by listening. hissssss
 
Andrew,
You're right, it is a pain. With the cold air box on my engine it takes nearly an hour to just get to the carb inlets with a meter, hose, or anything else.

Synchronizing at idle by air flow meters or hiss usually only sets the butterflys to the same opening. The pistons are usually fully seated at idle. Above idle, the piston position is what sets the air & fuel flow. I think that setting piston sync is more important than butterfly sync. They often are not the same due to variations of piston return spring tension & slightly different clearances between pistons & domes.

I much prefer some variation of the "wire" method. Actually I just stuff a narrow strip of thin wood (triangular cross section) down into the damper shaft, with a good friction fit, & mark a level on the stick that is even with the top of the dome. Then another mark at exactly 1/8" down. The friction fit lets you easily set the zero mark.

By disconnecting the throttle shaft coupling & individually setting the idle stops so that the piston lift is the same 1/8", (you may end up with a 3000 rpm idle in order to get the pistons to lift this far) locking the shaft coupling, & then backing off the idle stops equally to the desired idle rpm, you will get the best part throttle & full throttle response & likely the best idle also. AND it is easier to do.
D
 
I ended up making a set of wires to fit the SU damper bore - basically a very thin bronze brazing wire bent into an 'L' shape - 4" x 5" with bends in the 5" side to grip the bore.

Don't know how fussy you should be but I made sure the original bits of wire were both EXACTLY the same length so that they weigh the same. Point them at each other and watch the rise and fall of the pistons. Tweak to get them the same.

Worked a treat /ubbthreads/images/graemlins/england.gif
 
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