Can adapt motorcycle mercury carb sync tool to SU?

[58Custom]

I just got an old mercury type carb sync tool for motorcycles. It uses vacuum hoses that connect to a vacuum port on the carbs (kinda like the one on the pix below). Has anyone adapted one of these so they can get some indication of sync on HS4s?

 

[twas_brillig]

No experience with the above, but:
I'd try putting a piece of plywood over both carbs and drilling a mounting bolt hole through for each carb, then use ??? to paint the face of the SU, bolt the plywood in place to transfer the pattern, then drill 1 hole near the bottom of each carb throat to take the tester's metal tube, and drill a 1/2"(?) hole above that to allow some air flow, and give it a shot.
Or just duct tape across the bottom half of each carb inlet, poke the metal tube through at the bottom, and see if that would provide enough results to carry on with something more solid and repeatable.
Any other dumb/wise ideas?

Doug

 

[jvandyke]

I used those things quite a bit on bike carbs. I made one out of clear tube run around the edge of a yard stick, loose ends to carb vacuum ports, filled with gear oil, the readings don't matter, just that they're equal. That's the only problem, SU's don't seem to have a handy dandy port to take vacuum from. The bikes I did this with all had ports on the intakes for just this purpose but they had no balancing chamber either. Doug's idea above to "make a port" seems feasible, wonder if there would be enough vacuum to show on the gauge that way though?

 

[twas_brillig]

I've got an old Unisyn for tuning carbs, which featured an aluminum 'ring' to go over the SU intake and an adjustable spring loaded dish that you could close down on the ring (or back right out) to put a greater or lesser restriction on air flow entering the carb. There was a clear plastic tube with a light weight pellet in it that connected to the 'low pressure' side. You adjusted the air restriction until the pellet was part way up the tube, and then moved it from one carb to the other and adjusted the carb until you got the same pellet position. It didn't seem real sensitive to being centred on the intake.

The plywood/duct tape idea should work; the duct tape could give you a rough idea of how much of the carb inlet needed to be covered to give you the vacuum you needed, and then just pick an appropriate sized drill bit for that high tech piece of plywood.

Would just using your three hands to hold the gauge up and hold the business end of the tubing right at the bottom of the carb slide on both carbs give you a reading?

Doug