Dellorto Idle Jet Change??

[William2]

I have adjusted my carbs with a Synchrometer and the engine ticks over quite well and picks up with no flat spots. The Dellorto DHLA40E carbs with the fine threaded idle type screws are screwed in by about 2 1/2 turns to achieve a satisfactory tick over. This is in conjunction with size 50 idle jets. Should I leave it at that or try using a slightly larger idle jet so that the adjustment screws can be set at about 3 1/2 turns? The fact that the engine pops a bit, is that a sign of a slightly weak idle mixture? I have not touched the idle bypass screws, they are fully screwed in. Engine is standard SE spec.

[Wevster]

Hi William2
I'm surprised no one has given you a response so I will, i'm no expert however, interestingly I have just changed my Dellorto 'H' carbs for 40E the same as yours. I couldn't get them to idle with the the idle jets which they came with, which were marked 47, so I tried the idle jets from the H carbs marked 55 and the idling issue was cured.
Before tackling mixture make sure carbs are synchronized, I also used a airflow meter to do this, start with the first carb and match each barrel, I think I went for the strongest reading and adjusted the weaker barrel to suit using the idle bypass screw on one side only. Once your happy with that carb move onto the second and adjust in the same way. When the 2nd carbs matched with itself, use the control lever screw slowly and adjust to bring both carbs level.
You will have to adjust the idle screw accordingly, mine is set at around 9000 rpm.
You say your mixture screws are screwed in 2 1/2 turns, when I did mine, I screwed them in all the way and then out 3 1/2 turns. When the motor was fully warmed up I adjusted using a colour tune, which only meant a 1/4 turn here and there to achieve the blue flame just coming into the orange.
Hope this makes sense.
Good luck

Kev.

[William2]

Hi Kev, thanks for your advice. As far as I am aware only DHLA40 and 40Es' should be fitted to Elans as they are the most tuneable so it was probably a good idea to swap yours.

[Wevster]

Yes, I think you're right, the 40H's were fitted by a previous owner, so its nice to get back to the original equipment.
They would probably benefit being on a more modified twink, Alfa etc, so if anyone's out there in the market for a nice set of Dellorto DHLA40H they would be for sale.

Kev.

[mbell]

If the only issue is the number of turns of the idle screws and everything else is good I'd leave it well alone. If it ain't broke don't fix it, and I don't consider 1 turn broken.

(Disclaimer all my experience is with Webber carbs)

[nmauduit]

If the only issue is the number of turns of the idle screws and everything else is good I'd leave it well alone. If it ain't broke don't fix it, and I don't consider 1 turn broken.

(Disclaimer all my experience is with Webber carbs)

if it is like on Weber carbs, too small of an "idle" (low rpm really) jet will get lean mixture when fueling the progression jets before the main takes over...

[mbell]

if it is like on Weber carbs, too small of an "idle" (low rpm really) jet will get lean mixture when fueling the progression jets before the main takes over...

I agree. The idle screw being adjusted significantly away from the target turns could well indicate miss-sized idle/slow jet. My point was I consider 1 turn within normal adjustment window and wouldn't be changing the idle jet based on that unless there was a drive ablity problem, emission problem or other data source (e.g. A/F gauge) to show a problem.