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Discussion Starter #1
Does anyone know an easy way of measuring the balance of the Dellorto carbs and how to adjust them?

I haven't got any airflow instruments yet and was wondering if there is anyway of testing to see if they are unbalanced.

Cheers
 

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One way is to open the hood while engine is idling and with hand try to accellerate a little. After few test you might be able to hear which carb is staring first or if they start both at the same time. You dont have to rev the engine a lot , just a simple pull on the same spot as the petal connects to . Couple of hundred rpm will be adequate .
 

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you can build your DIY vacuummeter :)

this is the link- i will just translate he important part of the text

Sinkronizacija karburatora

you need a plank, 10 meters of transparent plastic tubing, some junctions for that tubes, and if the vacuum is too strong you need some pressure regulators (can be found in zoo shops, it is used for aquariums)

you pure some antifreeze in the tubes and the goal is to have equal amount of liquid in each tube.

i am to lazy to try it myself...but i will one day :cheese:
 

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The original factory adjustment was based entirely on careful setting of clearances on the throttle operating levers, so actual flow measurements were not necessary. This was a good thing, as I had read that some tuners just use a length of hose to listen to each intake to make air correction adjustments. I made a "steth-a-hose" to do this and found that each intake tract makes a different noise, even when properly set up!

All I did was adjust all of the air bypass screws to the same setting (they only affect idle quality anyway), I can't remember what value they were, something like 2.5 turns out from fully home. Each carburettor throttle stop was adjusted so there was 1.5mm (I think) of free play before the butterflies opened, and that was it.

Lauren
 

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Discussion Starter #5
you can build your DIY vacuummeter
this could be fun but not sure if I've got the time at the moment.

Greek: I'll listen carefully and see if I can notice any difference.

All I did was adjust all of the air bypass screws to the same setting (they only affect idle quality anyway), I can't remember what value they were, something like 2.5 turns out from fully home. Each carburettor throttle stop was adjusted so there was 1.5mm (I think) of free play before the butterflies opened, and that was it.
Never really understood fully what the air bypass screws do:confused:
What is their purpose?
Is one of them attached to the distributor with a small pipe?

I thought we balanced the carbs by using the little adjusting rod with the ball joints on the end that snap into the throttle levers. Is this true?
 

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2.5 turns from fully closed did the trick with me as well. But my butterflies open instantly when I press the throttle - no clearance there !
 

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Balance between the left and right carbs is adjusted using the screws on the throttle linkage. Balance between the two bores in the SAME carb is done by using the air bypass screws. This is done first on both carbs before attempting to balance left and right carbs.
In Europe the air bypass screws often have a lead plug tapped into the hole to stop people messing about with the settings. Check yours, you may need to drill/dig it out.
Buy a Morgan Carbtune - much easier than trying to make you own!!
 

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Discussion Starter #8
Air bypass screws

Has anyone tried using the air bypass screws in dellorto DRLA carbs??

I have the front left barrel just very slightly out of sync, stronger vacuum than the others.

I washed and replaced the o-ring on the bypass screws but whenever I try to use this method of opening the air bypass screw the AFR goes crazy.
Even just slightly opening it up to reduce the vacuum to balance with the rear barrel.

My AFR gauge jumps up and down and the exhaust note goes crazy.

So I just leave them all closed and have a smoother balance even though this barrel has a slightly stronger vacuum than the others.

:confused::confused::confused:
 

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Discussion Starter #9
No takers on this one?:(

Anyone use the air bypass screws with success on the Dellorto carbs?
 

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If the bypass screw is not helping, try the idle mixture screw
for that barrel. The mixture setting also affects the vacuum.
 

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Discussion Starter #11 (Edited)
try the idle mixture screw
for that barrel. The mixture setting also affects the vacuum.
Yep that's what I've had to do Lonewolf. The only way.

Just wondering if anyone has had success with the air bypass screws.
Maybe a very rudimentary design function and not properly tested. After all they are old Italian designs.

Maybe the angle of the butterfly is slightly out of balance with the others but it is negligible. But me being a perfectionist it's hard to keep my fingers off.:cheese::cheese:

So I understand if the vacuum is stronger on this barrel and cannot adjust it, I make the mixture a little leaner as it has less air coming in.
 

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I guess the designers of the DRLA and DHLA didn't expected
this high lifespan of these carbs. As i know they were produced
since the middle of the '60s !

Later the similar thing happened to the Bosch K-Jetronic injection system.
 
A

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Balance between the left and right carbs is adjusted using the screws on the throttle linkage. Balance between the two bores in the SAME carb is done by using the air bypass screws. This is done first on both carbs before attempting to balance left and right carbs.
In Europe the air bypass screws often have a lead plug tapped into the hole to stop people messing about with the settings. Check yours, you may need to drill/dig it out.
Buy a Morgan Carbtune - much easier than trying to make you own!!
As already set above you should firstly balance the two barrels of the same carb. To do this you should connect the vacuum gauges, then gently fully screw-in both bypass screws. Unscrew one of the two until both barrels give same vacuum reading. Repeat same procedure for the other carb. Remember that on each carb one of the two bypass screws will remain fully closed.

After you finish with the above you should adjust the linkage that connects the two carbs so that when depressing the throttle both open simultaneously.

Butterflies free play should be set to maximum 1mm.

Next stage will be the mixture adjustment of each of the four barrels/chokes individually.
Vacuum readings may be altered after the mixture adjustments, so repeat the bypass screws set-up again. Mind that only minor adjustments may be required.

Finally adjust the idle speed.

Good luck.

P.S. By-pass adjustment screw on the single choke Dellorto FRDA 32F (Series 2 model) is adjusted differently.
 

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Discussion Starter #14
Unscrew one of the two until both barrels give same vacuum reading. Repeat same procedure for the other carb. Remember that on each carb one of the two bypass screws will remain fully closed.
Yep done this procedure so many times with my vacuum gauges.
But the carbs just don't seem to like me adjusting the air bypass screw. So I end up with them all fully closed.

It's just 1 front barrel with has a slightly stronger vacuum than the others.
When I unscrew the bypass screw just even slightly everything goes unstable.
I've cleaned an replaced the o-rings.

So not sure why. Probably not worth any extra effort as it works good enough. Just wanted them all perfectly matched which is tricky.
 

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Yep done this procedure so many times with my vacuum gauges.
But the carbs just don't seem to like me adjusting the air bypass screw. So I end up with them all fully closed.

It's just 1 front barrel with has a slightly stronger vacuum than the others.
When I unscrew the bypass screw just even slightly everything goes unstable.
I've cleaned an replaced the o-rings.

So not sure why. Probably not worth any extra effort as it works good enough. Just wanted them all perfectly matched which is tricky.
The Dellorto 40 DRLAs on my twin cam have the air by-passes. I have them all screwed in hard as I could never get consistant settings with them. Webers don't have and there is no way to adjust slight inbalances on the 2 barrels of one carb.
Personally I would screw yours right in and concentrate on balance across the 2 carbs.
Morgan carbtune is best bet.
You could set the clearance equal from the linkage to the carb, but this is only accurate if the idle position of the 2 carbs is identical.
Before I had the Morgan Carbtune I would do this.

With engine of, wind back idle screws until butterflies are shut. Achieve this just shut state on both carbs.
Now open both idle scres by exaclty the same amount.
Now start car and set idle speed adjusting both sides by the same amount.
Set the throttle linkage clearance exactly the same on both sides

Should be pretty close now. Any better requires some kind on manometer (Morgan Carbtune)
 

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Discussion Starter #16
I have them all screwed in hard as I could never get consistant settings with them.
Good to know it's not just my carbs. Appears to be a good design trick but in reality it doesn't work for mine.


I find the hardest part is getting the throttle linkages the same height, the clip on ball linkage is tough to replace and hard to get off.
 

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The quickest and easiest way to balance the carbs basically from L to R is with an aerosol of carb cleaner.

Warm the engine fully and have it at idle, then spray some carb cleaner into the intakes for one carb(take the top off the airbox if standard). You will notice the rpm will drop - the engine may even stall. Then do the same for the other carb and listen for the rpm drop.

You may find one carb makes the engine drop significantly more rpm than the other, meaning they are not balanced and one carb is doing more work than the other.

Simply adjust the stop screw on the linkage arm to increase/decrease idle rpm on each carb until you have an even drop in rpm from both carbs, and i nice idle speed. :)
 
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