First Things First, I'm talking about a '78 Triumph Spitfire here, not any Volvo. Hope y'all don't mind, but the issue is, I believe, applicable across makes and there are more than a couple knowledgable and helpful folks here.

The backstory: A good friend is at his wits end trying to get his '78 Spitfire to run correctly. He must be desperate because he lent the car to me to try and diagnose. Me, a person who has never tuned a carburetor, much less two SU carburetors (just found out I can't spell the word either).

The car: '78 Triumph Spitfire, 1500cc, converted by PO to dual HS4 SU carbs, 4-2-1 header. Electric fuel pump, new Pertronix branded distributor and coil, new cap, rotor and wires. Carbs were supposedly recently rebuilt by PO, current owner sent them to Joe Curto recently.

The symptoms: As it came to me, starts and runs pretty good when cold. Hot, it has a lumpy idle, misses as it takes up throttle. Stumbles and struggles under load until 3k rpm then it pulls like I think it should, good power.

What I've done: Starting with the assumption that the carbs are just fine, I tried to find fault with the ignition system. Cap and rotor show no obvious signs of faults, plugs gapped. Per Pertronix, I checked voltage in the red wire, ground and voltage tests at the coil, all sat. Owner had the timing way advanced at idle, I removed the vacuum advance tube, backed it up to 10 BTDC and confirmed that it advances at higher RPM.
What else can I check? Pertronix claims that misfiring and breaking up under load is nearly always because of low voltage at that red wire. I moved it from the + side of the coil to the same switched power circuit as the fuel pump.

From there I moved to the induction system. Spraying carb cleaner all around didn't change idle except for the onboard ends of the throttle shafts. Are they to be sealed, or is it normal for the clearance in the bushes to allow fluid past?

I've assumed that the HS4s are working good internally. This based on the fact that they've been in Joe Curto's hands recently, they don't dump fuel out the overflow, and the damper pistons rise and fall freely and evenly. Another thing, there's no FPR just a little plastic gauge between pump and carbs that steadily indicates ~2.75psi.

I followed the guide at https://sucarb.co.uk/technical-hs-type-carburetter-tuning-general to adjust each carb.Adjusting throttle plate, backing off fast idle adjustment, setting jet height, resetting throttle and choke interconnections, setting idle speed and synchronizing (thanks Ron Kwas for your insights @sw-em.com) All went well until the last iterative step of adjusting jet height. Eventually I lost track of how many flats each one had been turned and which way. As it sits, the mixture is too rich (raising the piston lifting pins raises the idle and stays there); When I started the adjustment it was weak, idle dropped when lifting the piston.

I should go readjust the jets, but I get the feeling it won't make any difference, nothing so far has.

So I put it you, dear friends, what am I missing here and where should I go next?

Thanks so much for taking the time,
Will
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XC60 / Odyssey