The van's been acting up lately: starts nicely, idles well, accelerates properly, and so on, but at mid or low throttle, at all speeds in all gears, there is a kind of constant light stumbling, like it's just not firing consistently. It's almost imperceptible at times, at others it's enough to cause problems up long hills. It feels like the van has the tremors. It goes away decelerating or freewheeling, so it's definitely an engine thing. I'm pretty sure it's an ignition problem. Gapped the points (which are are pretty new), re-timed, adjusted valve clearances, and changed fuel filter - no improvement. The carb (original Solex 34 PICT-3) has been reconditioned this year with new spindle bushings. Vacuum hoses are all in order. The coil is of unknown age, as are the HT leads. Number 4 plug is cross-threaded and I don't know how long it's been in there (I know, I know, but I'm dreading it), the others are a couple years old. I suspect the coil, which sparks but not super brightly when I test, but I have no comparison so I dunno. Any other ideas? Anyone else had these symptoms? What are the typical symptoms of a worn out coil?
I would swap the coil first for how much they cost. Failing that possible air leak & running lean. If you can get it to play up while driving pull into a layby & switch off without letting it idle. Whip a plug out & check the colour. If its white it’s running lean. It should be brown colour if the mixture is ok. Misfire under load is often a sign of a dodgey coil
Can someone who knows tell me if my diagnostic method of putting the timing light on each plug lead and revving it to see if it the strobe starts stumbling to identify if a lead or plug is at fault has any basis in fact as it seems to work for me.
Replace coil, plugs and leads. Check vac advance on dizzy, if you have SVDA. Then, if still misfiring check the oil, see if it has any metal sheen to it.
I’d check the breaker gap and condenser as a cheap starting point. Then swap the coil out if you’ve got a spare. One thing at a time... Might also be manifold chilling, which feels like a big flat spot. Is your warm air feed to the carb working?
I've checked and rechecked the points gap, so I'm pretty sure that's not it. The warm air feed should be ok, but I will add it to the check list.
Does the coil get very hot? friend of mine had similar problems on a mg and suddenly the coil blow the end of it off while travelling (never heard of this before) but changed the coil for a ok spare and now all is well. (fingers crossed he said!)
I am going to put my neck out and say this could also be an over rich mixture due to maybe a too high float chamber petrol level. Or simply carb icing if you dont have unblocked exhaust heat risers and a proper hot air feed into the air cleaner. Mine was playing up a bit , subtly juddering from time to time yesterday before and after the incident outbraking an '05 Astra in a T2. Either that or whack a Transit... Pootling around Dorset never really warming up, and the vacuum advance plate in the distributor may be sticking where I didnt file quite enough off the ali base of the Accuspark module to make it fit a real Bosch distributor.
