Brian,
Air balance is quite straight forward to adjust if you have the proper equipment, namely a manometer system measuring manifold vacuum (best) or a synchrometer measuring air flow (a distant second place).
Initial setting is all air bleeds are closed, only one per carb should ever be open, unless you really, really know what you are doing.
These air bleeds should only be used to balance within a carb. Carb to carb adjustments are intended to be balanced with the balance screw on the throttle shaft, between the carbs of a 2-carb system like the Elan.
I use a manometer system measuing manifold vacuum simultaneously in multiple ports. The the bleed screw on the higher vacuum reading (lower flow) port is opened until its vacuum signal equals its paired mate’s. Remember, opening a bleed screw, lowers vacuum (and increases flow) on that port. Balance within that carb is now complete. Go on to the next carb and do likewise.
Finally, balance carb to carb with the linkage.
One might have to repeat the process to get a finer balance, but it’s the same process repeated.
When I bught replacement carbs to replace my DCOE-18’s, I elected to get a matched set of 40DHLA E’s because of the features they offered, namely 5-progression holes, vacuum taps, and air bleeds. The goal was off idle tuneablility and the resultant improvement in torque characteristics and driveablility. All DHLA’s are also reported to have superior fuel automization verses DCOE’s. We’ll see.
By the way, the pecking order for DHLA’s, the way I understad it is:
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DHLA C’s (5-progression holes-extended transition possible or tune like DHLA’s, air bleed balance, vacuum tap, non fixed idle air bleed, best of the range)
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DHLA E’s (5-progression holes-extended transition possible or tune like DHLA’s, air bleed balance, vacuum taps, fixed idle air bleed, long nose idle jets, first emission carb)
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DHLA’s (no suffix, 3-progression holes-meant to get on the mains early, non fixed idle air bleed)
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DHLA H’s (5-progression holes-extended transition, air bleed balance, vacuum taps, fixed idle air bleed, true emission carb tho)
These should be the only models of interest to Lotus folks. I view the DHLA E’s and DHLA’s as a toss up, depends what’s important to you, trade of air balance verses idle mixture range. I’m told the rest of the range are primarilly emissions carbs. The first 3 above are highly tunable with the DHLA H’s less so and reportedly slightly less power.
Bill