Hi I have owned a restored Petter M type for the last year. At the first rally of the season it ran fine all day, but since then it will only run for around an hour, after which the plug it too sooted up for a spark to jump the gap, therefore the engine stops. Replacing the plug means the engine will start straightaway. The obvious problem would then seem to be that I am running the engine too rich, but if I cut the fuel back any further it spits and coughs and misses and so on. I used to be able to cut the fuel back quite a lot more without this happening, but now I can't. I have tried various spark plugs including Champions and old lodges (which have been most successful but still not going much over an hour). A while ago I removed the adjuster needle form the fuel chamber and found the taper on the end to be quite burred - is this the likely cause of my problem?? I have tried various loads to run the engine under but this doesn't make much difference in the long run. Any suggestions would be greatly appreciated as I am only 15, and not yet very experienced.
Thankyou.