03-05-2018, 11:46 AM
Reviving this old thread, as it may be of interest to some of you.
I have been working on a classic car - not a Seven - which has been standing for a couple of years. Having now got it ready for the road, I have been experiencing very similar symptoms to Hugh's: the car would start and idle easily, but once on the road and under load, I was experiencing extremely rough running and almost total loss of power.
Eventually, a new set of spark plugs seems to have been the cure. Apparently, under rich-mixture starting, the stale fuel deposits a gummy coating on the electrode and the plug shorts out under load.
It has been suggested that one of the causes is modern plugs no longer have fully-glazed insulators and are therefor are more susceptible to contamination under rich-mixture conditions. I have not heard of this problem with Sevens - perhaps their plugs are still made to the old specification - but it may well be worth further investigation if you have some other car with poor running problems following a lay-up period.
I have been working on a classic car - not a Seven - which has been standing for a couple of years. Having now got it ready for the road, I have been experiencing very similar symptoms to Hugh's: the car would start and idle easily, but once on the road and under load, I was experiencing extremely rough running and almost total loss of power.
Eventually, a new set of spark plugs seems to have been the cure. Apparently, under rich-mixture starting, the stale fuel deposits a gummy coating on the electrode and the plug shorts out under load.
It has been suggested that one of the causes is modern plugs no longer have fully-glazed insulators and are therefor are more susceptible to contamination under rich-mixture conditions. I have not heard of this problem with Sevens - perhaps their plugs are still made to the old specification - but it may well be worth further investigation if you have some other car with poor running problems following a lay-up period.