Please help. loss of power, jolting

[thomasbs56xx]

Recently purchased 1957 2 door saloon.
three trips to mechanic (plus more for another issue now resolved)
Car runs fine sometimes, others it jumps and lurches, loses acceleration and wants to stop, ignition light comes on.
Mechanic said after changing the fuel pump and some other bits (i am not very good at these things, possibly should not have bought a 60yo car) that he doesnt know what to do if the problem persists as it doesnt usually happen to a minor... If anyone has encountered a similar issue, I would appreciate hearing about what was done to resolve it. cheers.

[Dean]

I wouldn't have thought jolting would be the fuel pump. If you hear it ticking when you first put the ignition on, then it should be okay.

I have had these symptoms with stale fuel, if all the fuel in the tank is fresh then read on.

I'd suspect it's electrical, if occasionally you get a poor spark then the car is likely to run like a pig.

Check all your leads are attached correctly and do not appear old and broken. I've had trained mechanics not fit my leads correctly.

I would recommend taking out each spark plug in turn, attach the lead, rest it on the block and turn over the engine using the button under the bonnet. Make sure it's out of gear, but look at the quality of spark, it should be a nice flash. If one or more appears to be quite poor, then we need to look at what it might be.

[palacebear]

Had a similar problem. Car ran fine for 9 or 10 miles then started exhibiting the symptoms you describe. In my case it was over-rich mixture slowly strangling the engine. Bear this in mind as a possible cause but go through the checks that dean has posted above, as a more likely fix.

[martin418]

i had the same problem caused by a faulty new condenser i stuck an old one on and it's been fine for 2 years

[palacebear]

As indicated by martin418, its worth considering that there are some poor quality replacement parts on the market. They carry brand names which suggest good quality but they're made (to paraphrase the late and much missed Roy bmcecosse) in wooden shacks in far away lands.
Many on here will recommend The Distributor Doctor for ignition components. If you decide to start replacing components, remember to do so one at a time until you've eliminated the problem.

[oliver90owner]

A simple diagnosis required? When/while it is not running correctly, remove the king lead from the distributor and check the spark to earth potential. It should eadily jump about 8mm with a strong blue spark. If it does, the problem is likely downstream of the spark generation, if elecrical. A weak, or yellowish, spark that will not jump a large gap indicates the fault is before the end of that king lead. This is after all the connections have been checked out as clean, tight (so low resistance) and the contact point gap is correct.

Simple testing and observation is far better than changing components "willy nilly" which, if you are inexperienced, is likely to end with no spark at all and the possible wrong conclusion that the original fault must have been the ignition system.

[thomasbs56xx]

Thanks for your responses! Seems I have some investigating to do