Vacuum Port

[Pablo]

Hi there,

 

i will install a Set of DHLA 40 E Carburettors on my Car but i am missing the Vacuum Port for Ignition Advance.    Have anybody experience to install this missing Port later ?

 

Thank you all !

 

 

Regards

[Triumph-V8]

Must be a port in proper position related to throttle plate.

As overside of carb is occupied only possible position would be underneath.

At idle no vaccuum is needed as throttle is opened vaccuum should be generated.

 

But better idea is to change to electronic ignition with mapping

that can be connected directly to manifold pressure.

 

If you look on 123 ignition only the 123tune USB can handle that.

[2.5piman]

Hello Pablo,

 

you can't look at the vacuum advance for the distributor on it's own. Seeing as you have a non standard carburettor that would need to be set up to give a lean portion at cruising speed and the vacuum advance could then be utilised. If the carburettor is set up for pure performance then forget about the vacuum advance, it is purely an economy measure to allow the car to cruise with a weaker mixture and run smoothly.

 

Alec

[Triumph-V8]

Proper vaccuum advance gives better fuel economy in the range of 0.5 litre per 100Km when cruising.

As its for free and engine feels more crispy I would use it if there are no difficulties.

 

Alec is right that leaner mixture needs even more advance but also

reduced/part throttle benefits from more advance when being rich.

 

Expect up to additional 15 degrees from vaccuum advance as perfect figure

for max. vaccuum. This shows the benefit because nobody will doubt that

reducing normal advance by 15 degree will have a serious influence.

[2.5piman]

Hello Triumph V8,

 

"Proper vaccuum advance gives better fuel economy in the range of 0.5 litre per 100Km when cruising.

As its for free and engine feels more crispy I would use it if there are no difficulties."

 

Only if the carburation is set up for it, by itself it does nothing, except possibly cause engine damege?

 

Alec

[Triumph-V8]

Hi Alec, with no doubt you have to do it right

because in same areas of the mapping I am

driving with 45 degrees advance.

That can kill an engine!

 

But I did a lot of testing with my Megasquirt.

 

What you can do first is to let the engine spin at 3000 rpm and keep the pedal fixed than.

Try what gives highest rpm with minimum advance by adding advance step by step.

 

You will notice that initially from the 30 degrees the engine gets from centrifugal

the rpm rises fast and than there is a point where nothing more happens.

That will be about 45 degrees and it does not matter much if mixture is rich or lean

where I must admit I did no testing in strange AFR areas.

I prefered to go between 13 and 15 AFR at part throttle.

 

What I tried is to make ignition mapping to switch between two tables while driving.

Without a hickup I can switch between two tables, one prepared with more advance

and see if engine pulls better with that.

That is how I drove through the whole mapping and changing both mappings step by step.

 

Cheers

Andreas

[Pablo]

Hello Andreas, hello Alec

thank you for the fast Response, great Background Information !

 

 

Then there is no way to install a vacuum port.

Whatever, i will convert from Emission to non Emission Carbs, because i think they will work better then Emission ?  ( I hope so )

 

Pablo

[Triumph-V8]

"non emission" sounds funny!

You will need a 40mm plug in the front to lock the carb

otherwise there will be some emission anyway  :-)

.

They changed a little bit on the carbs adding an air bleed screw

if I am talking about the right version you are facing.

That does not make that difference in driving and mostly

I had to lock the screw fully for setup properly.

 

If the engine runs good I would not change anything!

It might go to the bad side!!

[Pablo]

 Sorry, pre Emission Carbs meant. "  DHLA 40 E "

 

Now i can say its terrible to find a good Setting on DHLA L Carbs  with 34mm Chokes.

After a Long time (with Trial and error) i find a good Setting with 33mm Chokes.

The Engine has 300° Camshaft, Compr. Ratio approx 10,2 : 1, Bigger Inlet Valves, Machined Cylinder head, Sport exhaust System

So i think to achieve with Pre Emission Carbs and 34mm Chokes more power.

 

( Only the vacuum connection is not available )

 

Regards

[motov8id]

Pablo I think a wide band O2 sensor will greatly help you decide how to tune your carbs. The vacuum advance aids the the transition from idle to open throttle and the vacuum is gone once the throttle is open.