I have been having issues trying to tune my carbs lately on my 69"S". They have been running very rich, to the point they are fouling plugs (Champion N9YC) and I can wind the mixture screw up as far as it will go. It still runs and indicates running rich on my colortune plug. I tried dropping the float levels with no change to richness. I had noted that when the mixture screws were fully wound up, the top of the jet was marginally lower (about 0.4mm) than the bush that it sits in.

Today I reset my needles to be lower than the usual method of the shoulder being flush with the bottom of the piston. Before I centred the needle, I set the shoulder height of the needle to be flush with the top of the jet. It seems to have done the trick and I can now see a noticeable difference when idling. I can actually get the colortune to show a blue colour set at 6 flats lower than top.

Just wondering if anyone else has had similar issues and has had to resort to lowering the jet.
Is it a sign of wear in the needle and jets?
I am currently running GP needles in my 1 1/2" SU's. From memory I think, they are somewhere between No.7 and BP on SU charts.
What needles are used on Police "S"?

Regards Fritzie

CP4 needles with Blue dashpot springs

I run #6 with blue springs on my ex Police S. Similar profile to CP4. Runs really well, starts easily, good idle and power band

Sent from my SM-A305YN using Tapatalk

_________________
1970 Cooper S SPO41

Just checked the Mintylamb site for SU needles. It looks like the GP is the same as a No.6 needle except that station 3, 4 and 5 are richer. Station 4 on the GP needle is signficantly richer. From Station 6 on, it looks like No.6 and GP needles are the same. I think that I might try No.6 needles, hopefully this may improve my richness at idle.

Thanks for that
Regards Fritzie

Ran BG needles initially as apparently fitted originally to the STP cars. Couldn't get a satisfactory idle, although heaps of go at higher revs. Found the #6 to be better compromise

Sent from my SM-A305YN using Tapatalk

_________________
1970 Cooper S SPO41

Yea Calver suggests ABY with 286 style cam . The first little bit of the needle is very critical coming off idle then pour it in .