Lotus Elan and Lotus Elan Plus 2 Forums

Both the butterfly discs on this DCOE31 have a small hole just above the lowest point.

A PO has filled them with solder.

Does anyone know why the holes were there in the first place?

I believe the 31's had this hole and it was to assist in getting a better idleing, as I remember the 18's dont have the hole and some people drill the 18's for the hole.......of course I could be talking b******s and will be corrected

Yes the holes where there to increase air flow at idle and to enable the butterflies to be slightly more closed at idle. This positioned the butterfly edge correctly versus the progression holes which reduced the tendency for off idle stumble. I guess they may have been soldered up to try to change the butterfly position at idle for some reason. I am not sure if all DCOE31's had them. Weber also had different angle butterflies that were fully closed at slightly different angles which achieved the same purpose of matching idle air flow needs and butterfly position versus the progression hole location.

cheers
Rohan

Rohan
I can concur with your statement
In John Passini's book "tuning & maintenance weber carburettors" the same reason is given for the holes however I don't think it was a complete success. I changed my 131's for 151's and found a great improvement.in the gasp/snatch when opening throttle quickly.