'Coughing' at high speed

[JOWETTJAVELIN]

At high speeds (over 45 MPH), my engine has developed a slight 'cough' or misfire every couple of seconds which sends a slight vibration through the car. I know of 2 jobs which need doing (exhaust manifold to downpipe needs sealing properly and HT leads look a bit past it), but am unsure if this is the cause.

The dist. cap, condensor, points and plugs were renewed not long ago.

Any ideas?

[ampwhu]

this happened to me coming down the M6 in the outside lane.

i pulled over and stopped. the car would start and tick over, but when i pulled away, the same happened.

i changed the fuel filter and it cured it.

failing that, it is electrical. you can rule out mechanical.

[JOWETTJAVELIN]

OK, thanks. Deffo not fuel problem as there is one of those glass filter things fitted, and it's flowing freely.

Reading about dodgy condensors makes me think... as do the HT leads.

[MarkyB]

Is the glass filter thing on the dashboard so you can see it at speed?
Try looking at the running engine in the dark to see if sparks are going astray.

[ampwhu]

make sure the leads aren't touching some bare metal as well.

[bmcecosse]

Just get rid of any filter - not necessary...... What colour are the spark plugs? May be dangerously weak........

[JOWETTJAVELIN]

Just get rid of any filter - not necessary...... What colour are the spark plugs? May be dangerously weak........

Last time I checked they were a grey-white and yes, the mixture was noticably weak then. But I adjusted the jet and it ran better with more power.... but not checked the plug colour since.

[bmcecosse]

It's either loose connections - or struggling for fuel supply at high demand.

[JOWETTJAVELIN]

Turns out it was running too weak as I richened it and have had no trouble since. Will check plugs after its done a few miles like this.

May be best to err on the side of rich.