Alfa Pages

[Brit01]

DRLA carbs!

Hesitation between 2-3000 rpm (also feels like it has a lack of power in the lower rev range).

Changed 52 idle jets to 55 and now it's bogging down when accelerating hard!

Can't seem to get an 'in between' progression.

I will try with some rampipes to see if extra air intake will help the progression.

Can a retarded timing cause a bog down? (apart from the obvious of too much fuel being pumped in and/or not enough air).
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

Next step will be to raise the height of the floats by 1.5mm or so.

They are fairly new and I set them at 6mm, same as old ones.
But I did notice when I tested them in water the new ones appeard much more buoyant than the old ones.

I think the level in the carbs could just be too low. Raising them to 4mm or so may make the difference.

If this doesn't work not sure where to go. Maybe checking out the throttle linkages/butterfly wear.
Or even leaks in some o-rings (pump jets e.g)
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Ian M]

There is a specific level that the floats need to be set at (cant remember it at the moment though) possibly 4/5mm.
One test is if engine stalls under heavy braking then they are set too low.
Ive had this happen but dont recall it affecting performance though.
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Presntly own
Red Abarth 500c

[Brit01]

Yes you're right. 5/6 mm.
got mine at ~6mm (new floats).
Will lower them to about 4.5mm.

I know these are very sensitive and just a mm can make the difference.
Bit of a fiddly job especially in the cold (winter down here) but will try to find time this weekend.





also another doubt:

I bought a DRLA service kit a while back and wasn't aware that there were different size needle valves and seats at that time.

What size should I be using for a 40 drla with 32 chokes?
I see there is 150-400.

No idea what mine are. Can this cause progression issues if they are too small
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

Matt from Eurocarbs told me to use 58/60 idle jets as the 52 factory ones are way too lean.

He also insisted the DRLA carb mixture screws should be 2.5 turns more or less.

Strange as the manual says 5.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Bobkelso]

Hi Brit,
just an other strange doubt of mine ''
did you verified the integrity of the plastic pipe
from motor to the brake servo units?

I read from others that if there is a very small air leak
brakes can still have decent power (also if not 100%),
so may be you are not noticing it, but motor can have
some small malfunctions like
- idle difficult to regulate or with vibrations
- hesitation accelerating from low rpm
due to air variously in excess depending
on how the damaged pipe is stretched
during the motor functioning.. ''
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Alfa 33

[Brit01]

Thanks Bob.

I did fit new vacuum pipes there and new jubilee clips but I will check them again for a good seal. Should be fine if all new I guess.

Just got back from the local machinist and had some idle jets drilled out to 60 and mains to 145.

New fuel filter also.
Tecfil for a 145 16v injection .
Bigger filter - less restriction and better filtration rather than those awful cheap inline filters you get to 2 bucks.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[RFlower]

Before getting into different jet combinations and other technical bits, which are not likely to have just changed themselves, first look for the simple solution.

First move is always to check and double check all the carb and manifold gaskets, then check again, renewing them if in any doubt.

Also, of course any vacuum pipes etc. on the engine side of the carbs for bad connections or damage.
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Dick Flower, Nr. Carcassonne. '94 Trofeo 1.4 ie (F), '93 Imola 1.3/1.4 ie (now for breaking) (F), '91 1.7 ie (GB)(spare car), '86 Sprint 1.5 QV (F). '87 VW Syncro camper (F), '73 NSU Ro80 (F), '99 Fiat Seicento (F)

[Brit01]

everything checked many times, linkages, both opening at the same time, pump jets, floats etc etc.

Now some Guy crofts members divulged some tests done on these Dellorto carbs and stated the 52 idles are way too lean and need to be increased to 55-60, also the mains are on the lean side.

If the new idles don't improve the progression then yes there must be something I have overlooked. maybe even a slightly malfunctioning vacuum advance on the dizzy.

But I've heard so may people have great success with increasing the size of the idles from 58-60-62 even.

I'll keep you updated.

Maybe it also depends on the quality of fuel.
Here we have awful fuel and varies from tank to tank. Imported from Brazil with 10% ethanol also. But just bad.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

Excellent!!!

60 idles and 145 mains in.
Really nice smooth progression.

A joy to drive now! Finally feels like it should.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[paulhide]

Very interesting. And how does that affect emissions?
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Owner's Club 33 Registrar. Now from P4 & S2 1.7 QV
http://www.alfa-pages.co.uk/viewtopic.php?t=5188

[Brit01]

we have no emission test here so not an issue. Sorry to be environmentally unfriendly!

Interested in getting an MSD unit or alike to improve combustion.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[RFlower]

The larger jets could still only be compensating for a minute air leak in the induction system.
_________________
Dick Flower, Nr. Carcassonne. '94 Trofeo 1.4 ie (F), '93 Imola 1.3/1.4 ie (now for breaking) (F), '91 1.7 ie (GB)(spare car), '86 Sprint 1.5 QV (F). '87 VW Syncro camper (F), '73 NSU Ro80 (F), '99 Fiat Seicento (F)

[Brit01]

There are no leaks. All new and been checked and replaced to be double sure.
I've found that air leaks tend to produce an unstable idle but this is not the case now.

Also Dellorto themselves confirmed the 60 idles work better.
Been some dyno tests by a member on GC's forum also.

Maybe 52's work better with good quality fuel.
The few people who have dellortos here have the same issue with 52 idles.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

I wish they would stop messing with the ethanol content in our crappy fuel here.

First with the 97 premium is was 0% , then it was 10% and now i heard it was 5 %.

I'm sure it messes with my detonation limits.

Well anyway it's pinging a little now so got to retard it a touch.
Wish I had one of those small knobs on the outside of the dizzy to adjust it.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

MSD ignition 6A and SS blaster coil on its way!

Ebay purchase to see what all the rage is about with these multi-spark CD systems (capactitve discharge instead of inductive).
Also multi-sparks for 20degrees of the crank movement.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Bobkelso]

Very useful post and nice conclusion with solution founded

After your experience I read about, it seam that it is common
that carburator jets should be personalized a little respect
standard configuration, because:

- more ethanol you have in the fuel and more big jets
are needed as ethanol has better anti-detonation power
but lower heat power respect gasoline (more fuel needed);
our alfa came from 20 years ago when gasoline was different;
actually usually they don't use more than 5-10% ethanol
because in that case it should be very pure to avoid to much
water in it (in brazil they use more alcool and judge jets but
all the fuel line of the motor, aluminium and rubber parts,
is modified to get no corrosion by alcool+water)

- more km the motor has more bigger jets are needed

- as you says to pass emission test on all the cars sorting
the factory jets can be a little in the small side by default..

- maniacs put different jets and ignition advance from summer to winter..
(I usually only regulate a little the mixture screws when summer and
winter are arrived, when the motor starts to have a slow return
to idlee and screws must be adjusted a little I know it is officially summer..'')
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Alfa 33

[Brit01]

new filters (EMPI)




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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

Just changed the idles back to .55 as I found the new electric pump was delivering more fuel and black soot began to come out of the tailpipe indicating a very rich mixture.

During my lunch break I will get out and re-balance/tune them with the smaller idles.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

[paulhide]

Yes definite excess fuelling issue.
I've had this in the past with faulty pump jet diaphragms and leaking float inlet valves, but these come with hesitations or even misfires on initial acceleration and even stalling on heavy braking. In this case you can see the jets dripping, with the inlet manifolds removed.
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Owner's Club 33 Registrar. Now from P4 & S2 1.7 QV
http://www.alfa-pages.co.uk/viewtopic.php?t=5188

[Brit01]

[Brit01]

Carbs bone dry while running so no leaky valves there.

I am suspecting the brake servo drum now
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[paulhide]

Maybe you know better, but wouldn't brake servo drum issues cause rough running with air going into bottom of carb and you would have poor braking?
I thought you were on the right tracks with the floats, but floats too heavy causing too much fuel?
I mentioned the leaking jets as the extra fuel caused the symptoms you stated.
I am no expert, so you may be right - just using my own experiences and remembering someone writing on here sometime ago that they believed that the floats can become less buoyant over time.
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Owner's Club 33 Registrar. Now from P4 & S2 1.7 QV
http://www.alfa-pages.co.uk/viewtopic.php?t=5188

[Brit01]

I think overfueling would result in wet or leaking dripping carbs. All looked very goog.
Floats are only two years old
Also valves are new. But anything can fail.

If there is a small hole in the drum then I believe the idle can still be smooth but pressing the brake unsettles this balance.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)