1980 T140

Well if it wasn't for the lack of spark I would have said look at the seal/gasket between carb and cylinder head and check that isn't split

 

My mates bike was doing same - found ecu had fault. Tapping ecu body after it cut out gave intermittent spark. New ecu from States - jobs a good one. Hope this helps

 

I had this Derek on my Jap crap & it was the coils. Hope you have fixed it!

 

If you have the original Lucas E.I. system, it will most likely be that, mine did exactly the same.
I binned the whole lot and replaced with Pazon (which personally I prefer to Boyer) E.I., and while I was at it I replaced the coils with a single dual output coil, binned the zenor and fitted a Wassel dual phase regulator/rectifier unit.
Also, because they vibrate a bit I fitted a Motobatt glass mat battery.
Result is, easy first time starter, (mine is kick start only), and settles down very quickly, despite high compression pistons and 34mm Mikuni carbs fitted.
I run one grade hotter iridium plugs, but if you are L.C. and original Amals, then standards probably best.
Having said all that, you may just have a bad connection on the low tension side of ignition circuit??.....but the Lucas E.I. unit does react like yours when they are starting to fail.
Graham

 

Yes I did similar and changed for boyer branston problem sorted.
Regards
Joe

 

I got my regulator/rectifier from BritBits in Christchurch as it is just down the road from me.
It is important to have smooth rectified supply to battery and electronic ignition, especially the old lucas system, so I would çhange this first. With the engine running you should measure approx 13.5 volts across battery, and when you rev it, it should stay under 14.5 volts.
I would bet that your lucas e.i. amplifier unit is failing because the supply is critical, modern Boyer and Pazon units are more forgiving with supply, but it is still important to have good smooth supply for the batteries sake as well.
Like you, I also worked my way through the dodgy crimp connections and replaced with soldered heat shrunk connections wherever possible.
The main reason I prefer the Pazon unit over Boyer is because the pickup coils are encapsulated into a machined billet backplate and the amplifier box fits neatly into tray under seat, leaving enough room for my usb charging socket.
As I said earlier, I also fitted a single dual output coil, which are smaller than one original coil, and reccomended by Pazon (bought it with kit)......I will post a picture later if you want, when on pc, showing how it all fits in.
Graham

 

I expect this thread should be in Technical really?...but I'm sure one of the moderators will move it if necessary.
Anyway, here is the picture as promised, in the tray at top is the E.I unit, at the bottom is the 12 volt auxiliary socket, and the usb adapter and charging cables sit nicely in the center.
All nice and dry under the seat, and the dual output coil bolts on the tray to right which carried the old coils. I would also recommend the Mottobat battery I have fitted, as they hold charge very well and are not as effected by vibration

 

Good work Derek, and a neat use of existing housing.
Have you checked that you have a stable voltage at battery with engine running, of between 13.5 and 14 volts?
I would still recommend replacing the regulator/rectifier with one of the modern Wassell dual phase units, as the original zenner diodes have a habit of sudden failure, often wrecking the battery and sometimes even the E.I.amplifier.

My T140E is currently being treated to new sprockets, chain and swing arm bearings, and now it is a reliable first kick starter I just love riding it
Have you got spoke wheels, Lester mags, or Morris mags on yours?
Graham

 

Akront rims are aluminium, well-known and highly reputed.

 

Yes they are good rims, the four stud morris wheels can be a bit suspect (some say they are prone to cracking), but the lester six stud wheels fitted to export model seem to be ok.........mine have done 60,000 miles and I haven't managed to break them