Scooterotica

I'm getting the hang of setting up carbs, ie PHBH and TMX. Such as marking out throttle positions, plug chops and adjusting jets and needles. I'm also OK at establishing the correct pilot jet. However, I still find it a black art fine tuning the air screw, despite all the notes on the CamLam site and other sites.

For example yesterday, with a 30PHBH, I can turn the air screw in, which introduces more air and begins to rev, which in my current trial is 1/2 a screw out. I then turn the air screw out until it becomes really lumpy and ready for stalling, which was 2.5 times out. Then in between these settings, I cannot tell any differences. So, do I go for somewhere in the middle, which I did yesterday.

At this setting, I let it tickover for about 5 minutes and did a plug chop to find a black spark plug colour, but this is probably not the best method as it was not under load.
Alternatively, do I take it out on the road and do a plug chop at 1/8th and 1/4 throttle, where the air screw and slide cutaway have the greatest effect.

The trouble is, being an engineer, I need to understand and be precise and this air screw thing is driving me mad.

Tips please.
Thanks
Paul

interesting as I'm currently fiddling with my 26phbh on a mugello 225 with rs clubman 42.
110 main, av264/x13 2nd clip, 53 pilot and 50 choke and still massively rich in the 1/4 to 3/4.

air screw is set at 1 and 1/2 turns out, which I believe to be the recommended setting?

massively rich 1/4 to 3/4 is purely your needle/atomiser choice

rapido230 wrote:massively rich 1/4 to 3/4 is purely your needle/atomiser choice

I don't agree with that. The air screw on a TMX for example definitely has an effect there. Also the main jet at 3/4 throttle.

Also in disagreement ~ Massively rich 1/4 to 3/4 is purely your needle/atomiser choice