Carbs the squirty bit.

[exceliom]

Got my cleaned and rebuilt a few months ago but after refitting them I noticed a few errors on the rebuild ( like the floats were set way too low ) So I decided to Re rebuild them again, with a new kit from Eurocarbs.
Firstly I noticed that one set could squirt fuel across the garage when the throttle was opened, the other set would only dribble in comparison. I've changed components across and recleaned the limp carb.
Would I be right in thinking that the "super squirter" is wrong?
The squirt mechanism can be adjusted from the diaphragm on the bottom of each carb but what could be the right amount . Does anyone know how to set up this?
Any advice would be greatly appreciated.

[Lotus-e-Clan]

The super squirter is correct.

One full (quick, not slow) depression of the throttle should produce a set volume for a set time. If it's not quirting about a metre or so, then something is wrong.

You should refer to Des Hammill's tuning Book on Delortto and Weber tuning (search 'Des Hammill' on this forum or google for more info).

I have a pair of burettes for measuring DHLA accelerator pump volume, but you don't need them to get it 95% right.



IIRC of the top of my head, you're aiming for 5 to 7 ml per full stoke volume.

[CID]

Wow that's some nice equipment...

I've set mine off the car with some X squirts and measuring then the average fuel.
However that did not really worked apparently.
After installing, the AFR during acc. was however NIO. The car stopped accelerating.

So I just adjusted the amount until the car accelerated to the max (with GPS program) ... that's what the accelerator jets need to do anyway ACCELLERATE.

Rgds Curt

[exceliom]

Thanks, Lotus-e-Clan.
Would there be a chance that sufficient fuel is not getting to the diaphragm, I've blown all the passages out but could be missing something very obvious.

[Alan_M]

Ok, as you’ve rebuilt them, are you sure you fitted the diaphragms up the correct way? If one is upside down it won’t pump.
Is the free play/clearance the same for both levers?
Have you removed the pump jets and checked they’re not blocked, maybe swap pump jets from one carb to the other and see if fault follows.

[Lotus-e-Clan]

Also check the non-return valves in the pump circuit under the top cover.

There are wells under brass covers that house a weighted rod to hold down a ball bearing against the pump flow. These can stick (or hold debris) and restrict the pump jets of fuel.
Refer to no 24 in the diagram below. No 26 being the pump jet.

[LotusMonkey]

I bought Des' book recently and it is excellent, though weirdly I could not see a specific volume specified for the accelerator pump action, only a reference to there should be no free movement of the arm - i.e. that it should just be set so it is contact with the diaphragm base. I will look through again, as that is the information that I was looking for.

Mine were also built incorrectly and I basically have had to redo them myself.

Duncs

[Lotus-e-Clan]

Des's book is good. But there are one or two areas where he chooses not to got into detail, or doesn't fully explain function. Setting up the pumps is one area. Explaining the relationship between physical throttle balance achieved by observing the throttle plates passing the progression holes, versus setting balance via adjusting the bypass screws, is another. Many a tuner following Des's method for setting vacuum balance via the bypass screws (using 4 manometers) have ended up in a pickle by ignoring setting the physical throttle plate balance first.

[LotusMonkey]

Des's book is good. But there are one or two areas where he chooses not to got into detail, or doesn't fully explain function. Setting up the pumps is one area. Explaining the relationship between physical throttle balance achieved by observing the throttle plates passing the progression holes, versus setting balance via adjusting the bypass screws, is another. Many a tuner following Des's method for setting vacuum balance via the bypass screws (using 4 manometers) have ended up in a pickle by ignoring setting the physical throttle plate balance first.

Now I am scared - I bought that book expecting it to cover every aspect of getting the rebuild and setting up right, and reading your post I am now even more confused

[Lotus-e-Clan]

Des's book is good. But there are one or two areas where he chooses not to got into detail, or doesn't fully explain function. Setting up the pumps is one area. Explaining the relationship between physical throttle balance achieved by observing the throttle plates passing the progression holes, versus setting balance via adjusting the bypass screws, is another. Many a tuner following Des's method for setting vacuum balance via the bypass screws (using 4 manometers) have ended up in a pickle by ignoring setting the physical throttle plate balance first.

Now I am scared - I bought that book expecting it to cover every aspect of getting the rebuild and setting up right, and reading your post I am now even more confused

No need to be scared!

Thing is, If you follow Des's book, you will be 99.5% better off than not following it.

I've written a number of posts on here about setting the mechanical throttle balance by observing their transition across the progression holes.

An example on the pump lever set up. IIRC Des doesn't explain the function of the very weak spring on the lever setting screw. And that omission can lead to incorrect settings.

The very weak spring (looks like a Biro spring) should be set up to initially compress WITHOUT moving the pump lever. This is so the pump does not operate on very small, SLOW throttle openings (slow part throttle movements). But if you floor the throttle RAPIDLY, the spring will operate the lever as required, and you'll get the enrichment you need to cover the wide open throttle. If you set it to operate immediately on all throttle openings you will waste fuel, emissions will suffer, and your engine oil will get dirty very quickly (as well as from wearing the engine quicker).
You must keep your spring is good condition too. They can work-harden, rust etc. which will affect intended operation.

But some will ignore the logic of the intended operation of the pump spring just to cover a badly tuned ignition (too little part throttle ignition advance). Because richer mixtures will burn quicker than weaker ones.

Just bear in mind, Des is approaching tuning from an ex-Racer's point of view and NOT the OEM Delortto's original design brief. Racers never usually care about part-throttle operation, only WOT operation - which is the easiest thing to set up properly.

[exceliom]

Great advice there Lotus-e-Clan.
I've now got them sorted, both squirting.
Now to adjust the amount of flow? Should this be done in distance or calibrated against a number of pumps with volume?
Your advice has been excepional.

[Alan_M]

You’re aiming for equal volume.

This is also worth a read -

http://www.espritfactfile.com/carbbalancing.html

[Lotus-e-Clan]

Check all pump lever springs for uniformity. If they vary in strength or length or condition or rate (compression feel), then replace all 4 with new. Don't accept odd springs from EuroCarb, happened to me, and I insisted on them sending me a matching set of 4.

Only then can you expect to get them working as intended.

Next, bear in mind your ignition set-up. My 89SE has the later dizzy with plenty of vacuum advance, plus engine management tricks like the thermal ignition advance vacuum valve within the inlet water jacket. Optimised part throttle ignition advance set-up is key to avoiding flat spots on part throttle progression.

Similarly, make sure the progression holes at idle are behind the throttle plate on both carbs and that both sets of throttle plate progress exactly the same over the holes on each set of carbs. If not, you won't get the extra enrichment on slow part throttle openings when the accelerator pumps are not fully engaged (this is the point of the soft spring setting). Some folk have reported on here that their throttle plates won't sit fully in front of the progression holes when fully closed. This is a matter of plate alignment/centralisation on the spindle combined with manufacturers tolerances. If they don't sit fully in front of the plates, then it's not the end of the world, and it is what it is.

As Alan says, without burettes it is down to synchronising the pump levers to deliver fuel at exactly the same point in the throttle stroke when opening the plates RAPIDLY ONCE only (do not pump the throttles! ). When opening them VERY slowly, there should be a delay in the pump fuel delivery which approximately coincides with the throttle plate progression over the last progression hole (remove the brass inspection plates to observe the edge of the throttle plates traversing the progression holes).

Once the pumps lever springs are synchronised, aim for an equal squirt of fuel from each jet for exactly the same duration after fully (and rapidly), depressing the throttle. If the diaphragms are a matched set and the internal circuit is clean, then the delivery volume should take care of itself once the initial slow opening LAG point has been set via the Biro spring retaining nuts.

The pump Burettes make this all so easy, but like I said, you can get it as near as damn it without.

[exceliom]

Thanks Peter.
Again excellent advice in simple terms.

[DavidOliver]

Des Hammil covers the Dellorto very well in practical terms.
If you want to get deeper into Theory and separately Maintenance/Tuning look up John Passini on Weber Carburettors.
His editions are now 50 years since first published but nothing has changed, nor will for carburettors.
The weber acceleration mechanism is quite different to Dellorto but the concept is the same and John Passini makes interesting reading for anyone tinkering with carburettors.

Dave the cog.