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[Brit01]

Hi guys,

Just fitted 2 new pump diaphragms to my Dellorto DRLA 40 carbs.

I'm a newbie here, keen to learn, and mechanically minded.

When I press the throttle am I supposed to see a clear squirt of fuel from the jets circled red below? If not where could the blockage be?
Should I unscrew these and check for debris?

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[paulhide]

The diaphragms pump fuel up through channels to them, including any debris that may have been disturbed. Yes by all means unscrew them and clean them, but be very careful as once debris gets in these they are very hard to clean as the down facing nozzle is extremelt fine. The front end of these accelerator jets swivel and are shaped to fit in one way round only.
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[Brit01]

thxs Paul.

Got them out and gave them a good clean, also air blowing back through the fine holes. They looked all clear.

BUT when I pumped the throttle again I couldn't see any fuel coming out of the 4 of them.

Unlikely that the 4 are blocked or that both floaters are damaged.

Maybe a blocked fuel filter?

[paulhide]

Is there fuel in the carburettor reservoir? This is allowed in by the floats.
Is the channel from the diaphragm to the accelerator jets clear?
Have the diaphragms still got the springs with them?
Is the lever that pumps the diaphragm free to move.
Before the accelerator jets in the channels to them there are two sprung weights with tiny ball bearings. Are these free? They are beneath the two crosshead screws shown in the bottom of your photo near the accelerator jets. Try not to burr the screws as they may be rather tight.
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[Brit01]

Hi Paul,

yes I need to check the float chamber. I guess its because it doesn't have sufficient fuel in the reservoir.
Hoping its just this and not a broken float.



Channels clear yes, diaphragm spring fine and levers also.

need to get a new battery tomorrow and will try to prime the fuel chambers and get it running.
Then I will inspect to see if the jets are squirting well and also the ball bearings.
If not then I need to dive into the float chamber.
Never done this before but I'm a quick learner.

Cheers

[Brit01]

Ah yes also found out that 1 jet is 33, other is 35 and the other 2 are unmarked!!!

Not good.

What size is recommended for a 1.7 boxer?

[paulhide]

Mine have 35s
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[Brit01]

ok thxs, will buy a new set of 35's I think.

This week I'll attempt to remove the top plate to view the floats and inspect the chamber for debris.

Let me know if you have any tips/advice.

Is the removal of the idle/main jets as easy as just unscrewing them?

The remove the 5 brass screws (5 I think from memory) from the top plate, lift off and see the floats on the underside.

First time I've done this.

[paulhide]

Yes, removing idle and main jets is simple.
Be careful removing the top plate holding the floats that you don't damage the gasket in between or the choke spring.
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[Brit01]

Thxs Paul.

Just to confirm, circled in red is the choke spring right?
This could pop off when I lift off the plate.



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[paulhide]

yes that's the one.
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[Brit01]

Great thxs Paul.

This is not so complicated after all. Many people here said 'aahh no don't touch the carbs, take it to an alfa specialist (who will charge a fortune for 1 hours work!!).

I love mechanics and this kind of work for me is great fun, just got to visualise how it works and all the pieces before cleaning it.

The tricky part I know is tuning and synchronising them. I haven't touched the idle mixture or idle speed screws!

Just needed to replace the diaphragms, clean out the jets, and check/clean the floats/chamber for now.

[Brit01]

So far so good.

Manged to get 5 mins in the garage last night.

Removed the idle and main jets.

Idle: 52
Main: 142
Emulsion: 9164.4

Thank god all the same size not like he pump jets. Gave them a good clean.

Tonight's job is to remove the top plate and check the floaters.

Tomorrow I will take the pump jets to have them drilled out so they are all 0.35 mm.

[Brit01]

First time dismantling my dellorto.

Great. Very happy with myself. Got this far. floats and chambers in excellent condition.

Pump jets had to have them drilled to 0.45mm as 2 were oversized and couldn't get any new ones locally.
As long as they all match for now.
Would it be avisable to get these changed to 0.35mm when i can or are they ok left as 0.45mm?

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[Brit01]

Just been out for a test drive.
Nice!! smooth transition, left all the cars behind me at the lights!!

Idle timing was way out, set it back to 8 degrees and smooothhhhh.

BUT there is a tiny leak on one of the gaskets that is sandwiched between the float chambers and top plate.

Is it crucial I change this asap? Or will it be ok for a few weeks until I manage to get a new gasket?

[Brit01]

Been out for more testing.

There is still a slight hesitation sometimes under full throttle in 1st and 2nd gear.

Should I go up one main jet size or could the idle jets be a little lean??

I have 142 main jets now.

Also the gasket leak seems to have gone.

I will richen the mixtures a little tomorrow, half a turn maybe, if this doesn't improve the flat spot I'll try 55 idle jets.

[Brit01]

Much better.

I turned out the mixture screws half a turn and the flat spot disappeared.
Idling and timing still good.

Might be a tad rich now (it felt just a little 'heavy'), maybe 1/4 turn back in and see.

[BigAl]

Hey brit, have you tried balancing the carbs?
I can balance them but never tune them, i listened with the hose pipe but could never hear any difference.
Maybe this would help you if you are like me lol
http://www.dellorto.co.uk/merchandise/products.asp?CategoryID=8&PartsectionID=17

http://www.fastroadcars.co.uk/shop/index.php?act=viewProd&productId=209
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x2 33 16v
pictures http://www.alfa-pages.co.uk/viewtopic.php?t=5203

[Brit01]

In the process of doing that. Got a nice gauge, hooked it up to the vacuum port, but I think the gasket on the brass fitting is gone or dead, If I opened the port more than 1/4 turn the needle fluctuated, I assume air is leaking in through the thread of the vacuum port.

Have to connect it directly or put some washes on the ports.

BUT it does idle very smoothly, I'd be surprised if they were out.

[BigAl]

What type of gauge do you have? I believe you will need mercury ones to dampen down the pulsing effect.
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x2 33 16v
pictures http://www.alfa-pages.co.uk/viewtopic.php?t=5203

[Brit01]

[Brit01]

Just read a great tip to dampen the needle gauge.

Use the aquarium adjustable manifold fittings. Screw in the tap just slightly to create the damping effect.

I will try this.

[BigAl]

I am sorry Brit, i do not know, Paul ???
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