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Hugh,
A small amount of petrol in a well vented tank will go stale in just a few weeks whereas a full tank will last for months. I've also found that old petrol will exacerbate any other weaknesses (ignition or carb) which may not be evident when the fuel is new.
Peter.
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04-02-2018, 05:30 PM
(This post was last modified: 04-02-2018, 05:32 PM by Hugh Barnes.)
Well, after a number of weeks (to be fair, I was away for 3 weeks over Christmas and New Year) I have finally got to the bottom of this. After all the fannying about, well documented here, I drained the petrol tank, flushed out all the old fuel and refilled with a fresh gallon straight from the pump and all the problems went away..
Annoyingly, I had fiddled with different fuel as part of my trouble shooting, that was from a can I had to hand. I can only imagine that this engine, for what ever reason, is susceptible to ageing fuel..
thanks for all the advice and suggestions on this thread...
Hugh
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Location: Sherwood Forest
Car type: 1938 Talbot Ten Airline
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.
