Just playing Devil's Advocate (as usual), but my 89SE is still on stock OE jetting with no hesitation, all engine management gizmos in play, and 75K miles.
I've had it like this for about 25 years with no hesitation. However, when I first bought the car at 32K miles, it ran very badly, and it did not want to rev beyond 6K rpm. I never touched the ignition timing NOR the idle jet screw set positions because they still had their 'anti tamper' covers in place. I changed the plugs and leads, put V-Power in the tank, and it ran well after that. Unfortunately, some years later, a helpful, but ignorant, MOT man ripped off the 'anti-tamper' covers and twiddled the idle set screws because HE thought it was running too lean with less than 1% CO @ IDLE. So the helpful garage man set the idle screws to give 3% CO, ... because 'that's where old cars like this should be' ... IHO ... (well, we all know on here by now that an 89SE is
designed to idle at <1% CO!!!)
On the subject of idle jet holders (idle air correction) I have gained some useful practical experience tuning the Clan's DHLA's over the years. I have a good range of fuel jets, emulsion tubes, jet holders, and chokes to play with. I've tried many combos of jets, holders, emulsion tubes and chokes, measured against on-the-road, real world, AFR readings. To clarify a point, and in support of the chaps at Lotus who made the OE jet selection, the lean number 9 air corrector would have been selected for fine-tuning idle CO values at the idle set screw, without (during service) the risk of adding or subtracting too much fuel to the correctly-set progression circuit mixture.
The air correction holder allows fine-tuning (or otherwise) of the
mixture range available at the idle set screw, as well as
absolutely leaning or enrichening the mixture within the internal progression circuit.
So for the purpose of re-tuning
off-idle progression (where the hesitation is noticed in your case), the corrected mixture (for the state of ignition) can be achieved by either fuel jet selection, or indeed holder selection (assuming you keep the OE idle jet). But if you want to precisely home into, and sneak-up to, a target 0.5% CO
at idle using the idle set screws, then the OE No9 (lean) holder combined with the OE idle jet, effectively gives you more available turns of the idle set screw as you sneak up to the low idle CO target value of 0.5%. If you set the progression overly rich either by a larger fuel jet or via smaller air corrector holes in the holder (richer holder), then the idle set screw sensitivity is coarsened, making it difficult to dial-in a low CO at idle. And therefore a small turn of the idle screw will add, or subtract, significant fuel to/from the off-idle progression.
That said, if the DHLA's have air leaks at the butterfly spindle (worn), or they've been rebuilt carelessly such that the butterfly plates aren't absolutely concentric to the barrel, or the butterfly plate mechanical synchrony between carbs is off (often overlooked by using ONLY vacuum meters to balance carbs!), or there's an ignition fault, or there's a vacuum leak within the engine management system, or the engine's worn (less vacuum, low cylinder pressures), then making the progression circuit mixture richer may well indeed reduce the off idle hesitation. But it will also make achieving a low CO at idle (without misfire) more difficult to set, and moreover, a
small miss-turn of the idle screw, either way, could upset the progression mixture, frustrating the process, and the goal.
Sorry for long post, II can't help it, I have poor social skills
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