S.U needles

[Echezeaux]

I have just serviced my carbies as my car was running very rich, and found fews interesting things.
Two out of three floats were leaking, or sinking depending on the way you look at it !
Float levels at 19mm instead of 11mm.
And UZ nedles instead of UM.
I must say that the car was running quite right, bare the fuel consumption and the tendency to ping under load, even when cold, which you can attribute to the excess fuel - the ignition has been checked and rechecked, and the C/R too.
I haven't started the motor again, I will do it tomorrow.
Does someone know the difference between the UZ and the UM needle ?
Any thought welcome.

Thanks in advance.
Thierry

[christopher storey]

Pinking is rarely if ever caused by overfuelling - it is more usually a product of weak mixture and excess advance

I set out the dimensions of the two needles in inches at the 16 stations ( imaginary 1/16 inch points on the needle starting at the top) . The radii are of course half of these figures

[sorry, for some reason I cannot get the columns to line up with UM and UZ correctly at the top]

UM UZ
1 .1240 .1240
2 .1205 .1205
3 .1165 .1172
4 .1140 .1135
5 .1123 .1113
6 .1104 .1095
7 .1086 .1084
8 .1070 .1066
9 .1056 .1048
10 .1046 .1030
11 .1040 .1020
12 .1032 .1010
13 .1025 .1000
14 .1018 .0990
15 .1010 .0980
16 .1002 .0970

From this you can see that the UZ is mildly richer at the bottom end and a great deal richer at the top end. Bear in mind that the raw diameter figures minimise the difference. The real difference results from calculating the area of the annulus in each case through which the fuel flows, by using the formula [pi X 0.0625 squared] minus [ pi X radius of needle squared]

[Heuer]

[Echezeaux]

Well !!
First, Christopher and David, thanks a lot for the explanation.

I drove the car today after setting up the mixture.
The E runs so much better and it is not smelling over rich any more when started in the garage, even with no choke - just ask my wife !!
It was 43 C outside !! Good day to test the cooling system !
A bit of ping at the beginning, but after some spirited driving , it was gone for the rest of the drive, cleaned up the combustion chambers I suppose ?
All the temps were normal, but the CooKat fan had a good workout .
I should look out now how to reduce the temperature inside the cockpit !! I now, fully understand the meaning of the word ... cooking !!

Another lesson for me, never assume that the person who did the job, did it properly ! I have a nice invoice from the PO for a complete rebuild of the 3 S.U.

EDIT: UZ bottom versus UM top


Thanks again.
Thierry

[Heuer]

Fit Kool-mat - superb way of controlling heat and noise. Full details in the Upgrades sub-forum.