T140E
79, when I got it it had the spayed carb head and MK 2 carbs.
As one of your photos is of the exhausts, nearly all Triumph twin engines have splayed exhaust tracts (the few that do not are from the 1940s and 1950s).
The significance of the term is the inlet tracts - pre T140E originally have splayed
inlet tracts and, after mid 67, Mk.1 Concentrics; all T140E originally had parallel inlet tracts and Mk.2 Concentrics.
I advise checking the Boyer is wired properly (I have deliberately not typed "correctly"
):-
. Transistor Box White wire should be connected directly to the battery negative terminal, not anywhere else (e.g. not Boyer's "Negative frame ground" or other electrical nonsense).
. Box Black wire is connected to the coil's negative terminal.
. Box Red wire should be connected to the coil's positive terminal.
. The coil's positive terminal should be connected to the handlebar kill switch. This was originally a White/Yellow wire, the switch wire connected to the main harness wire inside the headlight shell, the main harness wire ran from there to the original coils' mounting area (where it also connected to the original Lucas Rita e.i. amplifier's positive wire).
. All electrical connections should be properly crimped terminals, not soldered nor the useless red (or blue or yellow) insulated hardware store junk Boyer supplies.
. As the MicroPower is digital electronics, each HT connection from coil to cylinder head must have 5,000 Ohm resistance but only 5,000 Ohms:-
.. a "connection" is the HT lead, the plug cap and the spark plug;
.. the spark plug can have the resistance - specifically Champion RN5 or NGK BR6ES with a parallel port T140 cylinder head;
.. if the spark plug code does not have the "R" in it,
either the HT lead
or the plug cap in each "connection" must measure 5,000 Ohms with an Ohmmeter or multimeter set to Ohms;
.. if using resistive plug caps (NGK?), these connect to the end of the HT lead with a self-tapping screw; be aware these always come loose - first test after a misfire is turn the plug cap clockwise
gently; if it never stops turning, the cap must be unscrewed and the short damaged length of HT lead cut off; thereafter (until the next time
), you should be able to refit the plug cap in the lead until gentle clockwise pressure cannot turn it further;
.. be aware resistive HT lead and resistors built into plugs and caps can fail and do regularly;
I prefer to avoid resistive HT leads and caps, using only resistive plugs and having spares on hand.
I'll do another jetting change
You did not fix the problem changing from Amals to Mikunis.
The Boyer MicroPower is notoriously unreliable.
Therefore, would you not be wiser spending the time checking the e.i. is wired as I have advised then determining whether the problem is carburation or electrical? Although you have muddied the waters for yourself by changing the carburettors before knowing for certain they were the problem, which has introduced the possibility the real fault could be masked by incorrect Mikuni jetting. Nonetheless, fiddling with the carburettors will not fix an electrical fault.
Just a long time owner of Japanese bikes too, the Japanese fitted them to all their bikes for years, constant pita. 
if a bike has to have HT resistance for digital electronics, I use resistor plugs.
