Alfa Pages

[Brit01]

Been getting a stubborn flat spot under hard acceleration.

I have 53 idles
142 mains.

I had 33 pump jets.
I changed them to 40 pump jets last night to experiment - got a nosedive and then good acceleration but obviously it was washing my cylinders as I lost some oil pressure.

With the smaller 33's I didn't get the nosedive, just a slight hesitation.

Should I increase the idle jets to 55 and keep with the smaller 33 pump jets?

OR keep the 53 idles and try 35 pump jets maybe?

Above 3000 rpm it responds just great.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Oggie]

I guess your new engine has standard cams, or have you replaced with fast road versions.
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PHAT 33

[Brit01]

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

[Brit01]

idles changed from 53 to 55. pump jets back to 33 ish (made locally!).
Started her up and she sounded smoooth. (all in under 30 mins)
Tomorrow if I get the chance I'll take her for a spin. May have to adjust the idle mixtures a little.

Also going to throw in some Motul 300v 20w/60 oil this week hopefully. (as opposed to 10w/60 as this will need to be changed more frequently and the car will never be started up in cold conditions so 10w is not really needed)
As my crank was on the limits of it's factory tolerance I want to bump up the pressure a little with the 60 viscosity oil.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Bobkelso]

Hi, Brit
what is the set-up before the air filter?

I mean, boxer on 33 with twin carbs usually have a thermic
operated valve before air filter, in a "y" plastic pipe before the filter box.

In theory that valve is closed when motor is cold,
to block cold air from main pipe from front of the car
and get only hot air from the secondary pipe from motor
hot manifold plates, and only after some minutes
goes fully open in the main pipe when motor is in temperature.

In practice that valve it is not so usefull to start the car
(because in the very first minute also manifold is cold!!)
and more over give problems as in few years the valve
leaks internal gas and remains always half closed,
depending also on the external temperature.

Before every regulation of carbs I suggest to remove permanently
that valve and close or redirect to the car front also the secondary
pipe that was pointing at the manifold (When my car was not with GPL
set up, I opened the "y" pipe, removed the valve and closed the two little
holes in the external plastic were there where the shaft ends of the valve
to avoid rumor from motor to escape; that 33 was never so fast
and enjoying to drive as after that little modification).

The car will start same way that before but motor will breath better
(you will see more rpm at idle) and always in the same way,
so it can be achieved a more stable carbs regulation (in principle
also some minor power gain because of slightly better air aspiration)
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Alfa 33

[Brit01]

No valve on mine, totally removed to increase air flow.

The small tube I have an extension in front of the radiator behind the grill for forced cold air induction at high speed.

Also a 63mm tube coming from the other to a hole on the front chassis just behind the bumper so it brings in cold air also.

Hesitation is normally caused by lean mixtures.

I have all this cold air coming in through a K&N panel filter so idle jets have been increased to compensate for this.

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

[Bobkelso]

[Brit01]

55 idles much better, but sometimes get a quick nosedive under very hard acceleration due to too much fuel going in.

What about larger chokes, say 34 instead of 32?
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Oggie]

Do you use trumpets, or the correct term velocity stacks?.
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PHAT 33

[Brit01]

no stacks.

Standard airbox but as mentioned I lengthened the large cold air intake tube, I have since reverted it back to the original length and will test it tonight.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

removed the bottom part of the airbox (as I've done before but was replaced for summer heat), and acceleration/response was so much better.

53 idles too lean
55 rich with a little nosedive

airbox opened to reduce restriction and with 55 idles works nicely.

Got to do some more testing but looks promising.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Oggie]

I had the same issue using 44 idf's, I ordered some spare jets and they were the wrong ones 50 I think(mine being 55) I tried them and the stutter under acceleration has dissapeared, they do tend to get blocked though, found blue silicon stuck in the last set I cleaned?.
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PHAT 33

[paulhide]

Sounds like you need 54s
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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]

jeje yes was thinking of that. There is an Italian guy on ebay who sells them. Got my 53's from him.




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

[Brit01]

I feel I can get another 1 degree of advanced timing without pinging. Still feels a little retarded at about 9 degrees.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

Looking at all of the jets where they squeeze into the main bodies (e-tube and air corrector part), I see they never join flush with each other.

Idles and mains. Always a few mm's to spare. I've see photos of others where the end jet part sits flush.

Should mine bottom out and sit flush?

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

[Brit01]

Checked all jets this weekend.
All bottomed out and flush as they should be. I was mistaken in the previous post.

All ok.

Didn't have much time but I'm suspecting it's running rich on the 55's and not lean. Can be a bit misleading sometimes.

If I had the original air intake attached (63mm pipe) to the airbox, it would hesitate under acceleration from light to 3/4 throttle. Only under full throttle it would kick in.

Then I opened the airbox to allow no restriction and the power kicked in much earlier leading me to believe it was starved of air and not lean at all. But under wide throttle it would hesitate a little(going lean).

I will install the smaller idle jets with the 63mm original air intake and see how it behaves.
Maybe going back to factory specs with the original airbox intake is what it needed as it was designed for. If I had open filter boxes on the carbs I'm sure I would need the 55's and larger mains but these suck in hot air from the engine bay.

(another issue occurred coming back during the last 2/3 kms) - a little knocking from the left front wheel hub area when turning the steering wheel either way. Have to remove the wheel and inspect all bolts. Hope it's not the outer drive shaft.



regards

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

[Brit01]

Really frustrating now.

Idle 52 jets in. Set up the idle and balanced them.

Idles and cruises at any speed smoothly. But acceleration under 3000 rpm is awful.

It hunts/surges/splutters (almost feels like it's running on 3 cylinders sometimes). Cruised at 130 km/hr for 60kms last night and that was just fine.
It can cruise in 3rd at a very low speed also without trembling.

Something is very wrong here. I will try the larger pump jets again with the 52 idles this time.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)