View single post by Esprit2
 Posted: 06-26-2019 04:22 am
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Esprit2

 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 512
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Alfa carbs, eh? Is there any suffix letter after the throat size... like 40C or 40E? When you get to 40H & beyond, those are 'emissions' carbs that sorta re-invented how DHLAs operate. They're a whole 'nuther discussion.

30mm Chokes ?! Those 'are' small for a 2.0 or 2.2. Even the Elan/ Europa's small 1.5 litre Lotus Twin Cam used Dellortos with 30-33mm chokes. I'm not aware of what chokes the JHPS site calls for (I'll take your word that it's 34), but the J-H factory DHLA 40s used 35 chokes. However, the standard jetting won't be of much good to you at 5200'... altitude is a very big deal to carburetors. The air gets thinner so the mixture gets richer. At 5200', a bone stock Dellorto J-H should be so rich that it will bog down, lose power, and belch black smoke. It needs to be leaned out. Despite the hiccups you mentioned, your engine reportedly runs well enough to indicate the carbs have already been tuned leaner than J-H stock.

Unfortunately, I have no experience with carbs at high altitudes... I'm a flat lander at 900'. However, Lotus Owners of Colorado (LOCO) has members running 907 engines in the Denver area, and J-H owner Jeff Rehman has recently completed a 2.2 conversion on his 907. There are folks who should be able to help you out. Jeff is using Weber DCOEs, but he worked through the altitude issues. Perhaps he could give you some pointers. I believe he worked with LOCO member Vic Cooper, who not only maintains his own very nice hotrod Lotus Esprit, but is an automotove pro who understands tuning for altitude. If you don't know Jeff, PM your contact info to me, and I'll forward it to him. Or go to the Jensen-Healey Facebook page... he hangs out there.

As for the popping on over-run. Have you played with the Idle Jet Holders (ie, Idle Air Correctors), or just the Idle Jets? Is there any off-idle hesitation?

Boring 40s out to 45s ? I've not heard of anyone doing that... no success or failure reports. Personally, I'd be more comfortable buying the size I wanted in the first place.

How are your Alfa Dellortos jetted? How about adding a column to the following:

Stock is TOO RICH at 5200 feet.
Jensen-Healey, Stock 2.0L, 8.4:1, C-cams . . . . . . . Your Alfa Dellortos
Carb Type. . . . . . . . . . . . . . . . . DHLA . . . . . . . . . DHLA
Throat, Emissions . . . . . (mm). . 40E. . . . . . . . . . . 40__ (suffix ??)
Throat, NON-Emissions . (mm). . 40. . . . . . . . . . . .
Choke . . . . . . . . . . . . . (mm). . 35. . . . . . . . . . . . 30, 34 on order

Main Jet . . . . . . . . . . . . . . . . . . 130 . . . . . . . . . .
Main Air Corrector Jet. . . . . . . . . 160 . . . . . . . . . .
Main Emulsion Tube . . . . . . . . . . 7772-5. . . . . . . .

Idle Jet, Emissions. . 5-Speed . . . 52L . . . . . . . . . .
Idle Jet, Emissions. . 4-Speed . . . 55L . . . . . . . . . .
Idle Jet Holder, Emissions . . . . . . 7850-5, LEAN . . .

Idle Jet, . . . . . NON-Emissions . . 50. . . . . . . . . . .
Idle Jet Holder. NON-Emissions . . 7850-1, Normal. .

Float Weight . . (grams) . . . . . . . 8.5 . . . . . . . . . .
Float Height . . (mm) . . . . . . . . . 16.5-17.0 . . . . .
Pump Jet. . . . . . . . . . . . . . . . . . 45. . . . . . . . . . .
Starter Jet. . . . . . . . . . . . . . . . . 70. . . . . . . . . . .
Starter Emulsion Tube. . . . . . . . . 7482-1 . . . . . . .
Needle Valve . . . . . . . . . . . . . . . 7180-15 (170) . .
Slow Running Rpm, 4-Spd . . . . . . 800- 850. . . . . .
Slow Running Rpm, 5-Spd . . . . . . 950-1000 . . . . .
I Prefer a Little Faster. . . . . . . . . . 1000-1100 . . . .

Idle Air Corrector Jet Sizes are in Random Order:
Leaner . . . . . . . . . . . . . . . . . . Normal . . . . Very. . . . . . Richer
7850-5, . . -10, . . -9, . . -4, . . -1, . . -3, . . -6, . . -7, . . -2, . . -8
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Similar

Regards,
Tim Engel

Last edited on 06-27-2019 04:22 pm by Esprit2