Lotus Elan

Weber Butterfly Query

PostPost by: AlfaLofa » Mon Sep 01, 2014 11:11 am

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?
001.jpg and
'64 S1 Elan (Owned since '73)
'69 Alfa Romeo 1750 Spider Veloce (Owned since '77)
'70 Morris Minor 1000 (Owned since '85)
User avatar
Fourth Gear
Fourth Gear
Posts: 518
Joined: 19 Aug 2006
Location: Scotland, UK.

PostPost by: types26/36 » Mon Sep 01, 2014 11:25 am

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 :roll: :lol:
64 S2 Roadster
72 Sprint FHC
User avatar
Coveted Fifth Gear
Coveted Fifth Gear
Posts: 3655
Joined: 11 Sep 2003
Location: U.K.

PostPost by: rgh0 » Mon Sep 01, 2014 12:10 pm

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.

User avatar
Coveted Fifth Gear
Coveted Fifth Gear
Posts: 7515
Joined: 22 Sep 2003
Location: Melbourne, Australia

PostPost by: Hawksfield » Mon Sep 01, 2014 5:32 pm

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.


+2s130 1971
User avatar
Third Gear
Third Gear
Posts: 389
Joined: 14 Jul 2004
Location: Hartlepool Teesside

Total Online:

Users browsing this forum: No registered users and 6 guests