Nissan Patrol 1990 TB42 - 4.2 Lt Petrol - Idling Issues

Having a lot of problems with a friends car. Idling to high and stalling if below 1000rpm.

Compression test was good over all cylinders. Around 175psi. No more than 10psi difference over all cylinders
New Spark Plugs.
Leads tested ok
Replaced Carby with aftermarket carby. No difference from old carby

New fuel filter.
Had to set rpm to 1800 so that when I dropped it would not stall when stopping. Rpm sometimes sits at 1100 other times up to 1800. Runs rough sometimes.
Replaced points in distributor Bingo perfect start idling St around 700 to 750. 1hr later had to adjust carby back up to 1800rms as it continued to stall.
Timing was at 20 degrees. Set back to 10 as per specifications.
Set points gap at 0.5mm. Specifications suggest 0.45 to 0 55.
No visible leak from intake manifold gasket or manifold
Set choke. No more black smoke.
Out of ideas.

Has anyone been able to overcome this idling issue?

No experience with the TBs personally, but petrols generally:

HT leads and ign coils can test OK but fail when hot. (my first suspicion since you didn't replace em)

I would also suspect vacuum leaks, either internal carb seals, or somewhere in the plumbing. You can check for this via the ol' garden-hose-to-the-ear, and listen for suck. Or by spraying WD40 around the joints and noting if the engine increases revs.

Also the carby could have fallen out of tune, or the seats/jets worn.
The needles and/or butterflies inside may needing to be re/set

Welcome to the forum. The new carby and filter has eliminated fuel delivery as the culprit. How old is the fuel in the tank?

What condition are the Dissy cap and rotor button in? Are the contacts clean and the small carbon brush long enough to contact the center of the button?

Is the coil compatible with the system? There are two types, one uses a resistor to drop the voltage. Check the points again to see if they are burnt already.

Thankyou Mudnut for your comments.

Quote:

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Originally Posted by mudnut

Welcome to the forum. The new carby and filter has eliminated fuel delivery as the culprit. How old is the fuel in the tank? - Fuel is new. No old fuel

What condition are the Dissy cap and rotor button in? Are the contacts clean and the small carbon brush long enough to contact the center of the button? Cap and Rotor look ok, slight crack in flat plate.

Is the coil compatible with the system? There are two types, one uses a resistor to drop the voltage. Check the points again to see if they are burnt already.

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I will need to check. All issues point to the Dissy, wiring, etc. Will need to investigate this area further.

Thankyou Mihit for your comments

I will check the leads further.

No vacuum leaks have been found.

Carby is new.

Issues are pointing toward the distributor and possible wiring. Will investigate further