engine misfire

[Joseph Dobson]

It’s me again.

 

My car has recently started to misfire seemingly without reason.  I have cleaned the plugs and installed new plug leads which seem to have made the problem more noticeable.  This problem disappears when the car has warmed up and we have done a few miles but is at it’s worse after start up and initial driving.  Any ideas ?

[BernieParticipant]

Joseph,

Could be a crack in the distributor cap – Changing the leads might aggravate that sort of fault.

If possible run it in the dark and look for stray sparks anywhere around the HT system.

Otherwise, perhaps the timing has slipped.  Suggest start by checking points condition and gap then reset timing.

Seems less likely to be the carb if the problem goes when engine is warmed up but if neither of the above, check for contamination in the carb and blow through all jets.

B….

[BernieParticipant]

……. and if all of those draw blanks, try changing the coil and condenser (one at a time, of course).

Failure of the condensor will probably result in heavily pitted points so there may be a clue when you check the points.

B….

[Richard LarterParticipant]

Not really relevant but I also had a slight misfire recently. I changed the coil and plugs which made no difference but I did notice it only occurred when the engine was hotter than normal especially on a run from Scotland to Norfolk in hot weather and heavy traffic, I could control the engine temperature with an electric fan. I considered fuel vapourisation and rerouted the petrol pipe between the fuel pump and the carbs when I got home so it avoided any hot spots and the problem went away. Result.

Cheers

Richard

[Joseph Dobson]

Thank you all for your advice.  A new set of plugs cured the problem so I guess plugs themselves are subject to malfunctioning.

Joseph

[Larry LewisParticipant]

What did the plugs look like when you removed them?

[Author]

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