Dellorto G Carbs

[William2]

Has anyone fitted Dellorto 40DHLA "G" variant carbs to their Elan? If so would you happen to have a list of all the various jet sizes and emulsion tubes fitted?

[elancoupe]

DHLA 40 F, G,H and so on are emissions carbs with limited adjustability.

The ones to use are, no suffix, C or E.

Tim Engel (Esprit2) is a member here, and extremely knowledgable on these, perhaps he will chime in.

[Esprit2]

I've not specifically worked with the G variant either, but Mike is correct, the Dellorto DHLAs to use are, "no suffix", C or E. The others, including the G, are generally either made specifically for some series production engine other than Lotus, or they're emissions engines. That's not necessarily bad, it's just that some have less adjustment range/ set-up flexibility, and may make it more difficult for you to get where you need to go. I don't know if the G will be a problem on the Twin Cam; but Lotus had it about right, and the further off the carbs are from the Lotus spec when you start, the more parts (money) it will take to get them into a working config for the Twin Cam.

You're starting with a correct 40mm choke, so the next key feature is the choke size. Lotus used 30mm chokes on the more mild standard TC, and 33mm chokes on the boy-racer Sprint. The larger the chokes, the more revvy and top-end happy the engine will be. Peak power will benefit, and low end grunt and drivability in traffic will suffer. The smaller the choke, more civilized and tractable the engine will be, sliding toward grocery-getter as the chokes get smaller.

The best approach is to be honest about your engine. If it's otherwise a standard spec TC, then don't try to turn it into a LeMans winner with just a set of carbs. Target Lotus' standard 30mm choke set-up. If it's a Sprint engine, then target the 33mm choke set-up. It really doesn't work to start with whatever choke size happens to land at your feet, and "fix it" with jetting. Choke size is the foundation upon which the rest of the set-up is built. Get it right, then go from there.

Is your engine standard, Sprint or hotrod? How big are your G's chokes, and what's the current jetting set-up? If the engine is mostly stock, and the chokes are out of the 30-33mm range, then think about investing in a new set of chokes and rebuild from there.

Lotus factory settings: Dellortos on 1558 cc Lotus Twin Cam:

..................................... Standard ............. +2, (all .................. Europa TC
..................................... Elan ...................... & Sprint ............... & Special
Carb Type ................... DHLA 40 ............... DHLA 40 .............. DHLA 40
Choke .......................... 30 mm .................. 33 mm .................. 30 mm
Auxiliary Venturi ......................................... 7848-1
Main Jet ....................... 115 ....................... 120 ...................... 115
Main Air Corrector ....... 210 ....................... 130 ....................... 160
Main Emulsion Tube .... 7772-5 .................. 7772-5 ................. 7772-1
Idle Jet ......................... 50 .......................... 50 ........................ 50
Idle Jet Holder .............. 7850-1 .................. 7850-2 ................ 7850-2
Float Weight ................ 10 gr, 7298-1 ........ 10 gr, 7298-1 ....... 8.5 gr, 7298-2
Float Height (mm) ........ 14.5 - 15.0 ............ 14.5 - 15.0 ........... 14.5 - 15.0
Float Needle Valve ....... 8811-150 .............. 7180.15 ............... 7180.15
Pump Delivery .............. 7.5cc/ 20 strokes ... 8cc / 20 strokes ... 8cc / 20 strokes
Pump Jet ...................... 7851.33 ................. 45* 8083.45 ......... 40 8083.40
Starter Jet .................... 70 .......................... 70 ......................... 70
Starter Emulsion Tube, 7482-2 .................... 7482-1 .28 ........... 7482-1 .28
Fuel Pressure (Psi) ...... 1.25 ? 2.5 .............. 1.25 ? 2.5 ............. 1.25 ? 2.5
....................... (kg/cm2) 0.087 - .176 ........... 0.087 - .176 .......... 0.087 - .176
Air Trumpet Length ..... 4.44 cm (1.75") ....... 40 cm .................... ?
Slow Running Speed .... 800 rpm ................. 800 rpm ................. 800 rpm
..................................................................... *35 if necessary
...................................................................... to improve driving

For Sprint & +2 engines with 'emissions' 40E carbs, the float specs changed to:
Float Weight ................................................. 8.5 gr, 7298-2
Float Height (mm) ........................................ 16.5 - 17.0

That's an overall lean condition. Starting from scratch with new carbs, that's not a condition you want to target. If you have such an engine, and it suffers from lean running, then try replacing/ resetting the floats to non-emissions specs before going off on any big effort to re-jet the carbs.

These factory settings aren't necessarily perfect. Emissions standards were creeping into the picture, and some factory specs reflected mandates more than best running. However, an engine with lean issues can usually be sorted out by playing with the floats, idle jets and air correcctors.

I included the Europa specs just for another reference point. It uses a smaller Main Air Corrector (richer mixture), but the lighter 8.5 gr float set to the same height as the Elan's 10 gr float will create an overall lean condition in the carb. Somewhere in there is a balance... of sorts. Also, the Idle Jet Holder (ie, Idle Air Corrector) goes from mid-range in the Elan to second most rich available in the Europa.

FYI, Idle Jet Holders (Idle Air Corrector Jets) are not numbered sequentially, but totally randomly. Don't get caught making any assumptions about which one is the next size richer or leaner. Go by the following chart:

Weaker .............................. Normal .... Very ...... Richer
7850-5 ... -10 ... -9 ... -4 ... -1 ... -3 ... -6 ... -7 ... -2 ... -8
............................................................ Similar

Sorry, no specific answers in all that. Just note that it doesn't work to compensate for incorrect chokes with jetting, or by turning screws. Get the chokes right first, the floats right second, then work out the jetting from there. If the G-carbs do have the right chokes for the Elan/ Twin Cam, then start by using one of the factory jetting set-ups above, depending upon the engine's state of tune (standard Vs Sprint).

Regards,
Tim Engel

[William2]

Many thanks for your advice. It seems to me that I would do better by selling the "G" carbs I have and looking out for a pair of carbs of the correct type.

[Esprit2]

If they're way off target from the typical Lotus Twin Cam set-up, then yes, that might be true. But for the record, what chokes and jetting are currently in your G-carbs? Look into the throat, and you should see a number stamped on the end of the choke. That's it's size in mm.

The carb will need to be right for the application. It's not simply a matter of bolting on something close, and then adjusting screws until it's right.

Go to the Eurocarb Ltd website and check out the prices of replacement chokes, emulsion tubes and jets to get some idea of what it will cost to reconfigure the G-carbs.

Eurocarb
http://www.dellorto.co.uk/
Dellorto DHLA Parts
http://www.dellorto.co.uk/merchandise/p ... ectionID=1

Prices in GB Pounds
13.60 each, 2 per carb x 2 carbs - Chokes
12.37 each, 2 per carb x 2 carbs - Main Emulsion Tube
_4.18 each, 2 per carb x 2 carbs - Main Jets
_4.18 each, 2 per carb x 2 carbs - Main Air Corrector Jet
_3.65 each, 2 per carb x 2 carbs - Idle Jets
_6.80 each, 2 per carb x 2 carbs - Idle Jet Holder (aka, Idle Air Corrector)
On and on...

Regards,
Tim Engel