I have been experiencing this problem for a month or so now and just ending up chasing my tail.
1973 Type 3 1600 duel relief with 32PDSIT carbs, JFUR4 0231 167 014 (311 905 205 T) Distributor with points
Car idle's rough when starting cold and will occasionally backfire through one carb when giving a few pumps while starting.
While warming up it will drop in rpm slightly every now and again.
When hot it still does this but also develops an intermittent misfire.
When driving under slight acceleration it will intermittently misfire.
Sitting at the lights it will hunt and sometimes misfire.
Under heavy acceleration it will occasional misfire but not affect acceleration.
When driving up a steep long hill the car will increase speed slowly and not bog down and get slower.
A few nights ago while driving it misfired a it and smoke came out the back. After that it ran a little better, but is now starting to misfire again. It pulls from any situation very well but needs a few extra revs when taking off from the lights (Nothing excessive)
Should say I also made my own gaskets for the carb to inlet manifold (x2 with the spacer) and inlet manifold to head
I have rebuilt the carbs not too long ago. Changed distributor (ran perfect for a day or two) , rotor cap, condenser and plugs. Point gap correct. Timing is correct so as not to ping going up hill. 98 octane fuel. Carbs synchronised. Valve gap checked a few weeks ago
The motor is in my opinion noisy and I have noticed quite a bit of back pressure through the oil breather. A couple of weeks ago I loosened the nuts holding on the heads, the retorqued as per the Bently but I am now unsure that they have sealed as there is still an exhaust leak type noise from the rear of the motor. Now I wonder if it is actually an exhaust leak. I do not have access to a compression tester.
I have wiggled the balance pipe with no change to the idle and the rubber hose connectors have been replaced and hose clamps are tight.
I have noticed that when the car is poorly tuned and running rough that the fuel consumption is no where near as bad as when it is tuned
Any help greatly appreciated as I need this car to get to work

how is ya coil i would chase electrics than exhaust leaks also toss a kit in the carby
if you can borrow a carby and see what happens,the more i think about it the more i like the carby i have just been through a hell finding a fuel fault with my 2 lit a tale for later

Carbs were rebuilt two weeks ago when I was correcting the accelerator pump discharge. Mine were both pumping out 0.9cc when they should have been between 0.3 and 0.5. Both still a little high but close to the upper specs. I make my own gaskets using a dud carb as a template. I may have another coil laying around. I have used two now and no change

dizzy cap and leads these are easy things that you would kick yourself if you spend when you don't need to
was it doing it before the carbys were kitted out

Well it all started a while back when I was travelling home. Started getting static through the rear speakers, car would bog down as soon as I tried accelerating and smoke poring out the rear. Tried rebuilding the carbs on the side of the road. It ran a little better for a few k's but still no acceleration. Then a god awful buzz that sounded like the world was going to end through the speakers and the car died. Checked the dizzy and the little button in the cap had been burnt and a strong smell of burnt plastic from the distributor. The Pertronics (sp) unit had self destructed. I put in a 009 to get home and that seemed to work quite well but the misfire was there. Thats when I rebuilt the carbs again, changed distributor, rotor, cap, checked valve gap, timing, points, plugs, changed coil, re tightened the heads, ect ect. The only thing I can't change are the leads as I don not have the cash to get a new set. The ones in there now have only twelve months use on them