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Thanks for all those comments and thanks Glyn but I head already read and actioned your advice about the exhaust divider as this was one of the things you wrote about in one of your Potty mods I believe.

So I took Chitty Chitty Bang Bang out for another 30 mile ride around Cheshire and caused a lot of consternation to riderless horses and small children.  before I set out i moved the needle to clip 2 with the air screw just over 1 turn out and she ran well to be honest but when it got hot things started to go wrong which I think is a lean thing, especially in that just on the needle bit. Once onto main jet, it’s fine.

So I stopped after 10 miles and turned the air screw in to half a turn out and moved the clip to 3 and this probably did not do anything except when going down hill and you back the throttle off whilst at the same time going fast, produced the most noise yet. Nothing I did would stop it and it can’t be good for the engine. The difference was though that it was coming out of the exhaust and not the carb so that’s backfiring which is rich. Next time I will turn the air screw to 1 again and if I would have had my wits about me I would have done it there and then but the noise deterred me. Having re read this posting, it seems obvious that I should choose to have the air screw out 3/4 of a turn.

Interesting to hear Leif on about the slide. I think it is a air/ fuel mismatch that affects some engines differently. I am inclined to agree with Richard that each bike has become slightly unique over time and likely also in manufacture.

I was going to stick the gauzes back and be done with it but I have a number 6 carb that is bigger than the 276 I have fitted so I am interested to see if what this does. As the internals are the same and hence the petrol flow, the increased bigness of the bore should mean more air and more spitting which I am growing to appreciate.

Going back to my Yamaha carb fiddling, either a less wide needle is to be tried, or a throttle cut out with less of a cut out. Or gauzes.

The Yamaha needles are all shapes, some with very skinny bottom bits and fat top bits and clearly Yamaha were imparting all their knowledge to get the mixture dead right to go to the trouble of having such widely differing profiles. You wonder if the bottom part of the needle on the Scott were skinny that it would help fuel flow in the very first parts of when the needle comes into being…………… Or gauzes.