Nissan 100NX 1.6 carb and cat issue

Hi all, OK so I'd better start by saying this is on a 100nx rather than a primera but Ive been advised you are the people who know these engines best, its a 1992 100nx 1.6 with catalytic convertor and hitachi carburettor.
I bought this car a couple of months ago, sold as ran fine before being put into storage but has stale fuel in, I know it was a gamble but couldn't resist.
I stripped the carb to find that the main jet had been sheared off and then the carb had been put back together again, also all the vac pipes were off. I sourced a main jet, reassembled the carb, put the vac pipes back on in where I think are the right places and the car ran like a Swiss watch... For about 3 days. Then I started getting problems with idle speed, one minute it's fine, then it's stalling, then it's ticking over at 1500rpm it seems to just do whatever it feels like. I did manage to get a used carburettor and swapped them over but the problem is still there so I'm assuming the issue is no longer with the carb. The other issue that has started is that after I changed the oil and filter, it decided it wants to sound like a vauxhall corsa, rattly timing chain, the chain was silent before, so I dropped the oil again and added an oil booster and this has helped somewhat, the timing chain rattle is now there one minute and gone the next. I used 10w40 oil.
So any suggestions are appreciated, could it be whatever controls the mixture solenoid? Lambda? (although I have had a multimeter on it and there is a signal) cat possibly blocked? (there is good pressure at the tail pipe, distributor playing up?
I was going to attempt a weber 32/36 conversion but not convinced that this will make my problem go away.
Like I said any help is greatly appreciated as I'm running out of ideas, I love the car but at the moment feel like torching it!
It's had. Plugs, leads, distributor cap, rotor arm, fuel filter, air filter, oil + filter etc...