Don't forget, Martyn is in AUS', Probably a bit hotter there, So would need a little richer than us ?.
Cheers Bill.
Cheers Bill.
E: Engine Comet Amal MK1 Concentric
- Thread starter Tony Wilkinson
- Start date
Martyn needs to look elsewhere, changing the main jet size is only going to save an engine on constant full throttle...........I would be looking at the slide cut away and the needle position to enrichen the mixture at more constant part and mid throttle settings. Retarding the ignition is not the answer either, as you are retarding it over the whole range, especially down in the lower rev range where a retarded ignition will make the engine run hotter. As Bill knows, sometimes a change in slide numbers is too much or too little, so a 3 might run rich and a 4 is too lean........It is quite easy to modify the slides several times to make changes without destroying the slide all together.
I have a 3 1/3 slide. and needle in middle groove but have now installed a .030 spacer under the clip to lift it a bit - the grooves in the needle at 0.060 appart. Reason I backed off on ignition is because I was told my piston damage was typical of detonation.
Detonation is equally ignition timing and fuel mixture. A single works pretty hard compared to a twin, so a mixture strength on the rich side is more desirable than too weak. Have you tried a number 3 slide, may be worth a try. The cutaway affects a large range of throttle, mostly from idle up to 3/4. I often modify slides to somewhere between say a 3 and a 3 1/2 to get a better mixture..........although we find plug readings difficult with modern fuels, you can still get some idea of a colour that shows either too rich (very sooty) or too lean where the electrodes look too clean. It can be a challenge to get right as you have found yourself.........