Dellortos conflict of opinion

[andrewdmoore]

There is an adjustment screw on the top of the Dellorto 40s on my Sprint that is blanked off/filled with wax. My current mechanic has found that the wax has been previously removed on one carb and someone has messed with the screws beneath and sheared the tops before refilling the hole with mastic.

A previous mechanic (a Webber/Dellorto service agent) says that these screws should be left alone as they are for Turbos only.

As these screws are so badly mashed, the current mechanic recommends getting a new carb body so these screws can be adjusted properly.

Who would you believe & what would you recommend I do?

Thanks, Andrew

[types26/36]

Andrew, if you are talking about the screws in the pic they are nothing to do with turbos, they are in the later carbs (including webers) and are for eqalizing the air flow through the venturi's of the same carb at idle.
On the older carbs there was no adjustment between the the two venturi's of the same carb, only between the two different carbs.
These screws are set at the factory and are not supposed to be tampered with but if you can set the carbs and each venturi has the same air flow then dont worry about it.

[andrewdmoore]

Brian,

I'll have to go back to the garage to check, but I'm pretty sure it was the screws in the 'turrets' at the top (the ones nearest the manifold) as there was 2 per carb.

Thanks, Andrew

[types26/36]

I'm pretty sure it was the screws in the 'turrets' at the top (the ones nearest the manifold) as there was 2 per carb.
Andrew

Andrew there are 2 per carb (no 1) it was just a bad pic.
No 2 (in the turrets) are the idle mixture adjusting screws and should not be sealed up.

[bill308]

Andrew and Brian,

The following link shows a labeled picture of a 45 DHLA. It must be a late model carb because it has all the features shown in the 40 DHLA E? photo. The layout is almost identical.

http://home.comcast.net/~jrkengr2/carbt ... ments2.jpg

I hope this helps.

Bill

[types26/36]

Bill,yes it is almost the same only the idle by pass screws are not sealed up on your picture as they are on mine and I presume Andrews.
I have never seen any reference to adjusting them in any manual and only seen them refered to as "set in manufacture" or "set by the factory"
The later Webers also have this system usually with a plastic cap over the screw with sealing compound as well although I have adjusted some on Weber carbs.

[bill308]

Brian,

Air balance is quite straight forward to adjust if you have the proper equipment, namely a manometer system measuring manifold vacuum (best) or a synchrometer measuring air flow (a distant second place).

Initial setting is all air bleeds are closed, only one per carb should ever be open, unless you really, really know what you are doing.

These air bleeds should only be used to balance within a carb. Carb to carb adjustments are intended to be balanced with the balance screw on the throttle shaft, between the carbs of a 2-carb system like the Elan.

I use a manometer system measuing manifold vacuum simultaneously in multiple ports. The the bleed screw on the higher vacuum reading (lower flow) port is opened until its vacuum signal equals its paired mate's. Remember, opening a bleed screw, lowers vacuum (and increases flow) on that port. Balance within that carb is now complete. Go on to the next carb and do likewise.

Finally, balance carb to carb with the linkage.

One might have to repeat the process to get a finer balance, but it's the same process repeated.

When I bught replacement carbs to replace my DCOE-18's, I elected to get a matched set of 40DHLA E's because of the features they offered, namely 5-progression holes, vacuum taps, and air bleeds. The goal was off idle tuneablility and the resultant improvement in torque characteristics and driveablility. All DHLA's are also reported to have superior fuel automization verses DCOE's. We'll see.

By the way, the pecking order for DHLA's, the way I understad it is:

1. DHLA C's (5-progression holes-extended transition possible or tune like DHLA's, air bleed balance, vacuum tap, non fixed idle air bleed, best of the range)

2. DHLA E's (5-progression holes-extended transition possible or tune like DHLA's, air bleed balance, vacuum taps, fixed idle air bleed, long nose idle jets, first emission carb)

2. DHLA's (no suffix, 3-progression holes-meant to get on the mains early, non fixed idle air bleed)

4. DHLA H's (5-progression holes-extended transition, air bleed balance, vacuum taps, fixed idle air bleed, true emission carb tho)

These should be the only models of interest to Lotus folks. I view the DHLA E's and DHLA's as a toss up, depends what's important to you, trade of air balance verses idle mixture range. I'm told the rest of the range are primarilly emissions carbs. The first 3 above are highly tunable with the DHLA H's less so and reportedly slightly less power.

Bill