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Hi All,

I've discovered erratic sparking on cylinders 5 and 6 of my FB (the engine is actually an FC engine) by using a timing light and connecting it to the HT lead of each cylinder.

I don't think it's the distributor and coil because I can draw a consistent spark from the end of the HT lead with an earthed screwdriver. I've cleaned and set the gap on the spark plugs, but no difference.

I've done a compression test and have 90psi on both cylinders. My book says it should be at least 115psi. Could this be my problem ? However, I don't see how compression would affect spark propagation...

I rebuilt the engine about 12 months ago. I had 0.060" oversize pistons put in and the block and head mating surfaces were machined. The valves of cylinder 6 were actually bent and the valve risers broken so I got new valves and risers put in. Don't know if any of this could be to blame.

Any ideas on my erratic sparking would be gratefully received.
Thanks
John

John,

Electricals can be fun
1/ Check the gap of the points on every cam lobe in the distributor.
2/ Check the side wear of the distributor shaft.
3/ Check the rotor button and cap for cracks or tracking.
4/ Replace the leads make sure they dont touch each other.
5/ Replace the plugs.
6/ Replace the condensor.

Do one thing at a time and test you will eventually find the prob
Hope this helps.
Is every cylinder 90psi or just the last 2?

Hi EK283,

Thanks for the tips. I'll let you know how I get on...

I haven't measured the compression of 1-4 since the rebuild. Before the rebuild they were around 120psi.

Thanks again
John