Adjustments for carb on 3Y motor

[Centretek]

I recently bought a 1986 HiAce but am having a hell of a time getting it to work properly.
The problem is major lack of power under acceleration/load and excessive fuel consumption (5.3Km/Litre).
By process of elimination, I believe it's a problem with the secondary/power throat.
I'd like to recondition the carb but damned if I can find a comprehensive guide on the 21100-73040 carburettor. I got a manual covering HiAces from 1983-1988 but it glosses over anything really technical.
Can anyone help with a manual that will assist an old fart to get his van working?

[ty.]

What kind of manual is it that you already have?

[Centretek]

Thanks TY
The only manual I could find is the "Gregory's Hi-Ace YH series [petrol] 1983-1989" which is fine for most things but skimps in the carby department, alternating between the "air valve type (mine) and the no air valve type. It doesn't have an exploded view of either carb , nor any pictures or diagrams of the linkages or their adjustments.
My problem is that the vacuum drops to nothing when the power cct. cuts in. It idles fine and has good vacuum at any RPM under no load conditions.
Did a compression test (175,175,175,180).
Replaced points and condenser.
Replaced vac advance unit (leaking).
Adjusting Fuel Mixture Screw seems to have little or no effect.
GOTTA have more information.
Is there something more in the 3Y Engine Manual ?
Thanks
Allan
Replaced fuel pump.

[Dazza]

The 3Y engine came from the factory with a major lack of power and excessive fuel consumption. You will get better economy out of a v8 engine.

[Centretek]

If I could afford a V8, I would have bought one.