Odd problem
 

My 122S has all standard ignition units IE coil (looks original) dizzy cap (new 2 years ago) and leads (same). Plugs are fine as is the points gap and timing. Over the last month after setting off and within the first mile or so, I experience the kangaroo type jerking of what seems like a huge miss fire. The length of time it happens for is increasing each time now up to a minute of jerking. BUT it only happens when I first set off on the first journey. The return journey so far has been trouble free. When it happens if I press the clutch the car will tick over and will rev freely without hesitation but the jerking recommences as soon as I let out the clutch and try to accelerate. Then it just clears. I suspect the coil is breaking down under load but that may well be nonsense so before I buy a new coil (don't have a spare one to try), anybody experienced this before? Car has run absolutely fine for 5 years prior to this.

I'm sure someone on here will have experienced this before.

nive;

I'm thinking it sounds like a fuel supply problem...check Fuel Filter, and Fuel Pump delivery volume..when its exhibiting these symptoms, try pulling Choke Control to see what happens...I've also seen throttle input be affected by sagging or even torn Motor Mounts such that when applying throttle, the motor rocks, which decreases throttle, so the motor settles back, which increases throttle...and this crazy cycle repeats with a bucking bronco effect...

Good Hunting!

Similar
 

Had very similar, was a clogged fuel filter as well.

I’ve been here with mine, turns out the rotor arm was out of position. Also the filter pancake box plate off the twin sus was wrong and blocking whole in the carb. The whole episode is a distant memory now I have 123tune fitted and a new adapter plate for the su to pancake box set up.

Fuel pump is new mounts are new choke makes no difference but thanks anyway Ron

Will check filter but wouldn't that be a problem all the time not just first thing. The engine runs well apart from about 1 mile into the journey

Don't disregard the advice so far but it sounds to me like an electrical heat related event. When it is cold there is a fault - once the engine is warm - pas de problem (!)

If I were you I'd check and clean all of the relevant electrical contacts - especially those that might get warm. It isn't a bad thing to do anyway - bit of white grease over a cleaned terminal before the winter shows a certain level of motoring dedication...

...I once had a kind of opposite electrical heat related problem with a multi-plug that had fallen too close to an engine => accelerating hard up a hill - suddenly you could only hear the wind! After considerable slowing there was usually a loud pop as the engine started again.

How about the fuel pipes and the tank vent?

Will check the fuel supply tomorrow see if there is an issue. The only thing that has been changed recently is a float chamber top as the lug holding one end of the float bar fell off followed by the float. I did wonder about float height as I carb could keep the engine running when not under load but it seemed fine when I checked it before installation.

Will have a look at that too thanks.