Dellorto Choke Size

[William2]

My S4 twin cam engine is SE and standard head spec and I'm trying to ascertain whether I should fit 30mm or 33mm chokes to the Dellorto 40DHLA carbs. Can anyone help?

[Esprit2]

Dellorto DHLA 4 Choke Size for Lotus Twin Cam:
Elan Std & ..... Elan Sprint &
Europa TC ..... Elan +2/ +2S
.... 30 .................... 33

Regards,
Tim Engel
Lotus Owners Oftha North (LOON)

[rgh0]

SE engines nominally came with 32mm chokes in Webers. i dont think I have ever seen any specs for an SE engine with Dellortos. Did Lotus ever make any as original equipment?

I would start with the sprint Dellorto specs and 33mm chokes as the cam and valve differences are marginal between the SE and Sprint and less than the fuel differences over the years since the original specs. From there you will need a rolling road dyno tune or a lot of playing with chokes and jets by trial and error if your not satisfied.

I dont know how easy it is to get 33mm Dellorto chokes these days. I know for Webers that you can only easily get even numbers i.e 30 / 32/34/36/38. so if Dellortos are similar you may need to go for 32 or 34 and do some guessing on the matching jet combination to start with

cheers
Rohan

[Esprit2]

Eurocarb Ltd is my preferred source for Dellorto parts.
Dellorto 33mm choke for DHLA 40 carb
http://www.dellorto.co.uk/shop/dellorto ... uri-choke/

DHLA 40 chokes are available from 25mm to 37mm in 1mm steps. All are available from Eurocarb Ltd in the UK. Matthew currently has eleven 33mm chokes in stock, and buys or manufactures replacements as required.

Early Domestic/ ROW Twin Cams (non-Federal) used Weber DCOE carbs. In 1972, Lotus switched from Weber to Dellorto DHLA across the board. In general, Weber jets and component sizes are spaced wide apart, while the steps between Dellorto components are very small. As emissions requirements grew tighter everywhere, even in non-Federal markets, it was easier to accurately zero in on perfect settings with Dellorto's finer resolution than with Weber's coarse resolution.

Later, Lotus revised their initial Dellorto settings for the Twin Cam. On Feb 12, 1974, Lotus issued Technical Service Bulletin 1974/1, revising the jetting for all models. I know, it starts out referring to the Europa TC first, but read on to the conclusion. The "Big Valve" specs also apply to Elans as noted. The Tech Data Sections of the manuals were to be updated to reflect the following settings.

Technical Service Bulletin
CLASS: .. 111
NUMBER: 1974/1
TYPE: ..... All Models
Date: ...... 12.02.74

Title: Workshop Manual Amendments.

Reason: To correct Technical Data as indicated.

Action:
1.) EUROPA TWIN CAM & SPECIAL
To page 7 of Technical Data, amend Dellorto carburetors settings, adding where necessary, as follows:

................................... ----- Small Valve ----- ....... ----- Big Valve -----
.................................... Domestic ... Emission ..... Domestic ... Emission
Choke ......................... 30mm ......... 30mm .......... 33mm ........ 32mm.
Main Jet ...................... 115 ............. 120 ............. 120 ............ 120
Main Air Correct Jet .... 160 ............. 200 ............. 130 ............ 160
Idling (Slow Run) Jet .... 50.02 ......... 45L .............. 50.02 ......... 50L
Pump Jet ..................... 40 ............... 33 ............... 45* ............. 33
Starter Jet ................... 70 ............... 70 ............... 70 .............. 70
Main Emulsion Tube .... 7772-l.28 ... 7772-5 ........ 7772-5 ....... 7772-5
Starter Emulsion Tube.. 7482.1.28 .. 7482-1.28 ... 7482-1.28 .. 7482-1.28
Needle Valve ............... 150.33 ....... 150.33 ........ 150.33 ........ 150.33
Idle Jet Holder ............. 7850-2 ........ 7850-4 ....... 7850-2 ........ 7850-1
.................................... (120) .......... (160) .......... (120) ........... (140)
Float Assembly ............ 7298-01 ..... 7298-02 ..... 7298-01 ...... 7298-02
Air Trumpet Length ...... 40mm ........ 40mm ......... 40mm .......... 40mm.
Colour Code ................ Green ........ Green ......... Red ............. Red
Part No. prefix - Front... N ................ P ................. Q ................ R
Part No. prefix - Rear ... N ................ P ................. Q ................ R
................................................... * Use 35 if necessary to improve driving

2.) ELAN + 2 -- To page 20 of Technical Data, amend Dellorto 'Big-Valve' carburetors settings, as in '1 ' above.

3.) ELAN -- To page 24 of Technical Data, amend Dellorto 'Big-Valve' carburetors settings, as in '1' above.

Regards,
Tim Engel
Lotus Owners Oftha North (LOON)