Dellorto DHLA40s

[JonB]

Some pix..

Carb for cylinders 1 and 2

Carb for cylinders 3 and 4

I'm looking for some advice on how to tune these beasts. I have a flow meter (fits to a single trumpet and gives a numeric reading) and Gunson's Colourtune.

First though, this gap, is it normal?

Carb - manifold gap

I think I am looking at the manifold O ring behind the bolt, where I expected a properly formed gasket. Is that right?

[el-saturn]

.........as there's even cobwebs which shows no cleaning or so...and the o-ring missing on one side (?) i imagine you should steal an hr somehow to give em a good clean an a set of fresh o-rings - that'd be one step forward!! sandy

[bitsobrits]

Gap is normal, and should be on both side of the intermediate plate between carb and manifold. There should be an O ring on each side of that plate, special spring washers (Thackery washers) under the nuts, and the gap adjusted per the manual. The plate/O-rings are an anti-vibration mechanism and the carb should never be fully tightened down.

Isn't much to tune on Webers or Dellorto's (assuming the jetting is already correct) other than carb balance and idle mixture. Numerous print and online publications out there (including the Factory manual) on the process. I find Des Hamill's book on to be very useful. How to Build & Power Tune Weber & Dellorto DCOE & DHLA Carburettors

[vincereynard]

Something like this -

Note the gaps in the thackery washers. Details in the manual. Fuel Section (L) Page 19.

They are shown in your first 2 images but with plain nuts (presumably) bolted tight.

[alan.barker]

On the studs you need thin plain washers + thackery washers+ nyloc nuts.
Imho the best for balancing Dellortos is a Carbtune.
Alan

[JonB]

So I am missing the Thackeray washers?

[vincereynard]

So I am missing the Thackeray washers?

You appear to have them but they are bolted down to have no mid coil clearance.

Also there is no additional plain washer and the nuts should be nyloc. With a plain nut what would prevent it vibrating loose and altering the clearance? (Hence bolted down.)

This will give no flexibility to the carb. mounting and could put a distorting strain on the carb. face.

Nasty bodge. But the bits are cheap. I bought new studs as well then they are all the same length.

Does your wife still recognise you?

[MarkDa]

You've got the special tools needed to equalise air flow and then optimise mixture.
After renewing the o rings and reinstalling the carbs it should take an hour or so -providing ignition timing is right.

[JonB]

Something like this -

(picture)

Note the gaps in the thackery washers. Details in the manual. Fuel Section (L) Page 19.

They are shown in your first 2 images but with plain nuts (presumably) bolted tight.

Carb pr0n! My carbs will never be as clean as that!

So, they're bolted tight. I had thought the engine on my car at least had been well looked after. Now I see that is not necessarily the case. It has multiple oil leaks too (but let's not derail the thread, I will start another at some point). Time to grab the manual.

[JonB]

Ah-ha! The Dellorto carbs are explained on page 63 (section L.26). Better get some new O rings, Thakerays and nylocks ordered...

[Edit: done!]

[JonB]

On further reading it seems there are not that many points of adjustment as has been stated above.

• Idle speed
• Idle mixture
• Acceleration pump capacity
• Butterfly position (balance)

Thing is, the carb is covered in screws that look like adjusters. They're not described in the manual, but at least one looks (from the cross sectional diagram) like a cover for the progression holes (fig. 29, item 23). I would like my car to run well, but I also seek fuel economy as I can tell it is running rich from all the soot in the exhaust. This takes me, presumably, into the shady realm of emulsion tubes and jets.

Maybe I can adjust the acceleration pump capacity thingie to reduce the amount of raw fuel it squirts into the inlet when mashing the throttle to the floor... as you do..

[MarkDa]

Jon
Most of the screws just hold something in.
Until you've remounted the carbs, balanced the airflow, set the idle jets and then run the car a while you won't really know if anything else needs to be done.
If not happy at that time next step would be to strip, check jet and tube sizes and clean carbs.
Generally on standard engines the standard set up works!
Mark

[vincereynard]

Here's a short article on tuning Dellortos. It expains what and where the tweaking bits are.

Tuning Carbs.pdf

(637.11 KiB) Downloaded 9571 times

[JonB]

Vince, that is just the ticket, thanks!

[john.p.clegg]

..and don't forget to set the float height first...

John