More DRLA 40 nonsense

Is it tops off and pump jets out to swap venturi's? I might take the DRLA36's down to 28's for a try

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Yep and the aux vents. You'll need smaller mains too, one or two sizes down from experience.

 

Following my Dell'orto Vacuum related post in the 'what have you done to your bay today' thread, this seemed a good place to share some nerdy DRLA 40 Information.

Most Dell'orto 40's have DRLA 40 stamped on the side followed by a Letter:
D (destra) for right hand side. S (sinistra) for Left Hand side. Most were used on Alfa's.

My carbs both have DRLA 40 B stamped on the side.
B type carbs were sold for in line use, suitable for a Ford Pinto or similar, nor for a boxer type engine used in an Alfa Romeo or VW air cooled.
The spindles would have been specific to allow in line linking, so depending on what you are going to fit them it may be a problem.
Thanks to eurocarb www.dellorto.com for the info.

As you can see from the photo my right hand side carb was modified to fit throttle linkage, prior to me buying it 16+ years ago and has worked fine in my VW air cooled engine.
DRLA 40 B don't have a vacuum take off/union and its best left that way apparently.

@zedders @snotty @areksilverfish you may or not be interested, but i've shared it here in case it is ever of use to anyone considering buying Dellorto DRLA B carbs!

 

I'm interested ! Does explain why you've got what you've got. You can live without the vac take-off. They are great carbs (if a little thirsty with a heavy right foot).

 

All Dell nonsense is good nonsense.

I nearly suggested in line for your linkages.

 

More Dell nonsense: the 45s on the MG are marked, variously A, P and no letter at all after the 45. Clearly not a matched set, but hey ho.

 

..interesting..good to know..thanks for the ingo Paul


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This is an idea that is stupid or maybe put EMPI out of business.
Most linkage's are a faff on dual carbs, don't open equally , lots of filing/drilling, swearing.
Or there's synklink. Dear.
Run two throttle cables. Right from each carb all the way to accelerator pedal.
Mind blowing?
Cheap?
Simple?

 

Ps what happened when you went to 32mm chokes?
Even with just 1970cc 'the dell book' says it's ok, so 2.4 should be in no way too big.
Im still choosing an initial set up (drla 36 tho).

 

Not as simple as a basic CSP centre-mount

 

Easy to set up and synch…. Even I can do it. Btw what idles you running. Mines still rich bottom end on 57s

 

I think

 

Me? 57s (although could maybe go down to 55s).

 

Nice idea but is there room for the cables to make a smooth 90 degree turn to run in straight to the throttle spindles. Then theres the custom lever on the end of each throttle spindle maybe one pointed up, one pointed down if you dont have left/right carbs, the mid- air bracket for the bowden tube each side., the two into 1 joiner just behind the pedal lever under the floor at the front, adjusters for length of cables not being quite right.
Problem is that engines are built with different widths and depending on spacers and manifolds the carbs are at different heights.. but you need precise sub millimetre accuracy symmetrical sideways movement at the carbs
And the carbs dont bolt down in precisely the same positions making the solid bar arrangments produce different results each time they are refitted .


Then the synclink cable system looks a good solution. All the complexity where you can see it in the engine bay and less demand on getting the carbs bolted down in exactly the same places.

 

Bigger chokes push the power up the rev range, ok in a car not so handy in a bus.

 

They also make jetting more dependent on float level as you get less suction from lower air speed through the venturi at the same air flow rate.
With relatively too large venturis the jetting only tends to work at idle and wide open throttle as tested in the rolling road world , with flat spots in the real world in between.
Its one of the reasons the progressive is a mess as it opens up its throat from 26 to 26+28 mm ( cant remember exact numbers but it more than doubles ) suddenly..

 

More likely it's the overlap between idles and mains which can be rich or lean or "just right" depending on the combination of every other changeable part.
Is that with your 30's or did you go down to 28?
Idles in a bus do next to nothing and only operate below about 2mm of pedal under driving conditions. Take your main stacks out and go for a drive and you'll see what I mean. The biggest effect they have on anything is starting from cold.

 

Don't forget it's a combo of capacity and max revs. The power and torque die over 4,000rpm on mine so I have nothing to gain by larger vents. The 32's are where I settled but there wasn't much in it between those and 30's. 34's were too lean at lower rpms cruise with correct WOT jetting. It's all a balance though and if my engine revved to 6,000rpm I would have perused main/air combo jetting for 34's.

I added the red stuff to this commonly referenced graph to demonstrate. Rough and ready guestimate but looks to me that 30's should be fine for my engine... which they are.


The Dell book may say 32mm for 2L but VW fitted much smaller on buses. There's too much info out there relating to cars that just doesn't work for heavy buses.

 

I think it's more that they allow higher revs so if your engine is designed to make power at higher revs then bigger venturis allow the air flow. Conversely with our stock or stockish cams making max power at lower revs, big vents are pointless. Rule of thumb is fit the smallest vents that don't choke the engine at it's max revs.

 

went down to 28s. I take your point and thanks for the comment. mains are 127s so not massive.