Alfa Pages

[Brit01]

Just curious - what vacuum readings are normal at each cylinder at idle?

I'm trying to finely tune my carbs (taking some practice!) and currently reading about 24 cmHg at about 850 rpm.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

Question:

Was playing around with the idle mixture screws while reading the vacuum gauge.

Why is it I don't see a change in the vacuum? I understand that the point of the highest vacuum is the sweet spot.

From 1 1/2 turns all the way out to almost 5 turns I had NO CHANGE in vacuum.
Very strange. So I'm a bit confused how to know if its running too rich or lean.
I've seen the engine hotter if it's less than 3 1/2 turns in. Less than 3 turns and it tends to rev high and takes a time to settle. Too lean!

Currently have them set at 3 3/4 turns which seems to many. While running in neutral standing still engine fan does come on every couple of minutes.

I have 52 idle jets.

I have some spare new 55's if I need to try these.

Engine was rebuilt 15 months ago and I'm running K&N panel filter.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

I've been busy today.

I took out the vacuum ports and saw that the o rings were all old, hard and perished!!

So replaced and cleaned these, also cleaned and blew out the mixture needles.

Put 4 new idle jets in also. (without measuring them I can visually see they are not the same size even though they state 52!!).

So tomorrow morning I will sync the carbs again with the 'refurbishment' completed.

Vacuum ports screwed in nice and tight with the new o rings.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[paulhide]

Good luck.
At the moment I have a carburettor misfire on light throttle (I've checked all other possibilities) which I'm trying to work out. Am going to change a complete carb to see if that resolves the problem.
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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]

Spent hours today trying to get the mixture right.

I actually put 55 idle jets in. The old worn 52's always seemed to be a bit on the lean side and of odd sizes visually.

Idle seems to be a bit unstable at the moment.
I get mixed signs of it being lean and rich.



(hole in the exhuast doesn't help with diagnosis of exhaust note!!!)

Currently about 3 turns out I think.

Now is it best to turn each one 1/4 turn while the revs continue to increase before falling or focus just on one cylinder at a time??


(when I turned the mixture screws all the way in the left carb had a half a turn difference in relation to fully seated position, is this normal?)





Maybe the 55's are just too rich but I wouldn't think such a small size increase would upset it.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[paulhide]

Size of idle jets WILL make a difference.

Yes, it would seem that it is normal that mixture screws settle at different rotations. They certainly do on mine anyway.

Changing the mixture screw in one place will affect the balance of the others, so you have to go from screw to screw till you have a balance that you are happy with.
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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

[paulhide]

SOMEBODY SENT ME THIS A FEW YEARS AGO (for weber carbs on various vehicles):

Rough running and idle is normally down to the idle mixture and balance settings being incorrect, below is a technique to establish a clean idle and progression. Before adjusting the carbs in this manner you must make sure that the following conditions are met.

i) The engine is at normal operating temperature ii) That the throttle return spring/mechanism is working OK iii) That the engine has sufficient advance at the idle speed (between 12 and 16 degrees) iv) That an accurate rev counter is connected. v) That there are no air leaks or electrical faults.

A reasonable idle speed for a modified engine on Webers is between 900 and 1100 RPM.

If you are adjusting the idle for a set of carbs already fitted then progress to the second stage, if the carbs are being fitted for the first time, screw all of the idle mixture adjustment screws fully home and then out 2.5 turns. If you are using DCO/SP carbs then start at one turn out. Start the engine and let it reach normal operating temperature. This may mean adjusting the idle speed as the engine warms up. Spitting back through the back of the carburettor normally indicates that the mixture is too weak, or the timing is hopelessly retarded. If this happens when the engine is warm and you know that the timing is OK, then the mixture will need trimming richer on that cylinder. Set the idle as near as you can to 900RPM.

Using an airflow meter or carb synchroniser adjust the balance mechanism between the carbs to balance the airflow between them, if the rearmost carb is drawing less air than the front, turn the balance screw in a clockwise direction to correct this. If it is drawing more air, then turn the balance screw anti-clockwise. If the Idle speed varies at this point, adjust it back to 900 RPM, to decrease idle speed screw in an anti-clockwise direction, to increase, screw in a clockwise direction.

When you are sure that the carbs are drawing the same volume of air, visit each idle mixture screw, turn the screw counter clockwise (richening) in small increments (quarter of a turn), allowing a good 5 - 10 seconds for the engine to settle after each adjustment. Note whether engine speed increases or decreases, if it increases continue turning in that direction and checking for engine speed, then the moment that engine speed starts to fall, back off a quarter of a turn. If the engine speed goes well over 1000RPM, then trim it down using the idle speed screw, and re-adjust the idle mixture screw. If engine speed decreases then turn the mixture screw clockwise (weakening) in small increments, again if engine speed continues to rise, continue in that direction, then the moment it starts to fall, back off a quarter a turn. The mixture is correct when a quarter of a turn in either direction causes the engine speed to fall. If that barrel is spitting back then the mixture is too weak, so start turning in an anti-clockwise direction to richen. During this procedure, the idle speed may become unacceptably high, so re-adjust it and repeat the procedure for each carb barrel.

After all the mixture screws have been set, the idle should be fairly even with no discernible 'rocking' of the engine, if the engine is pulsing, spitting or hunting then the mixture screws will need further adjustment. If the engine is rocking or shaking then the balance is out, so revisit with the airflow meter/ carb synchroniser. No amount of adjustment will give a good idle if the throttle spindles are bent or leaking air or the linkages are loose on the spindles!
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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]

Many thanks Paul.

I had this one printed out, with about 5 other manuals and instructions

If I can't get a good balance with these 55 idle jets then I think I'll need to buy new 52 jets (but I had the idle mixure scews turned out about 4 turns with these, always thought they were a bit lean).

The tricky part I've found is reconneting the linkages, this always seems to unsettle the idle. Shame you can't adjust these finely while they are connected.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

Silly quick question:

If the gasket and washer with the idle mixture screw are worn out/old can this have an effect on the adjusting?

Can I get an air leak through this?

I wasn't able to reach/remove the spring/washer while the carb was on the car but I did manage to clean the needle.
No idea what condition the gasket/washer are in. I do have new sets though.[/b]
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[paulhide]

I think they would have to be pretty knackered to let air pass them. I did have one spare carb recently which simply didn't have the washer and spring with one of the mixture needles/screws!
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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]

Knackered like the orings from the vacuum ports??
Hard and perished!!!!

Now I'm wanting to strip the whole carb but time is an issue as I have a 3 month old.



[url]

Uploaded with ImageShack.us[/url]
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

Just been out for a test drive.

Smooth acceleration, no stumbles! Nice
BUT the idling is not good.

it's smooth but erratic especially after stopping when decelerating.

Maybe an imbalance between idle stop screws??

Or an airleak? I will get some carb clean spray and spray around the joints while its idling to see any change in rpm.

I will also remove the throttle linkages to see whether the idle is the same.
Maybe they are slightly out but not noticeable after increasing throttle.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

Found a company on ebay that sells idle jets in small increments.

52,53,54,55.... etc.

I'm a bit of a perfectionist but not sure if it's worth getting the mixture down to this degree of accuracy.
My 52's were always a bit lean.
Now I've got 55's and currently trying to dial them in to get a good running at idle (acceleration and transition is much better than with the 52's but idle is still a bit rich).
Currently 2 1/4 turns out. (52's were 4 turns out and still a little lean with a stumble)

Would it be worth trying 53 and 54 jets? Or just stick with using the mixture screws turned further in with 55's?

Also is there anywhere else in the UK where I can buy cheap DRLA mixture screws with the hex heads and jets (apart from dellorto uk - they want to charge 8.95 for postage!!!! )?
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

It's a balancing game with the Dellortos.


Erratic idle much less but now more rocking of the engine at idle even though the vacuum readings are the same on both sides!!!
I adjusted the throttle arm on one side as I think this was causing the unstable idle.

Maybe a leak on one of the vacuum ports.

I've run out of lunch breaks at work to play with the carbs!! Lol

As long as it gets me home now.
Then when I have another hour back with the vacuum gauge.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

Too rich now? Backfire/popping on deceleration and idle!!

Acceleration is just great but maybe enrichment is going on and burning the excess fuel on deceleration?

(also got a hole on the exhaust right now)
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[paulhide]

Hiya, having an exhaust leak may not be helping your procedure!
I would imagine 55s are too big.
Yes you need to have carbs drawing in equal amount of air on both sides before tuning and then make sure linkage opens all butterflies at exactly the same 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]

[Brit01]

Got permission from the boss to work on my 33 this Saturday morning.


The other day driving back from work I thought I would just tweak the carb a tad, ended up screwing up the balance (starting rocking!!), and little fart backfires began under decel and idling.

I'm putting the backfires down to the unbalanced carbs, one side becomes much richer than the other.

I was balancing them before by removing just one throttle linkage. Maybe that's where I went wrong.

Tomorrow I will remove both and re-sync them until thet are silky smooth!! Fingers crossed the farting goes away and I can adjust the mixture so its not soo rich.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

Spent some time today syncing the carbs. Damn those throttle linkages are tricky to get right.

To get the carbs balanced is easy, the linkages are the most difficult part.

Pretty sure I've got an air leak. The air bypass screws are definately leaking, god knows what else.
Idling is so unstable. Being a little rich shouldn't make such an unstable idle. Even if I lean it in it is still unstable.

So I will be removing the carbs in a few weeks and replacing all the gaskets and washers etc.
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

Well my wife hadn't driven my 33 for a long time (before I started working on it), and she had to use it yesterday.

Even though I haven't finished tuning and cleaning the carbs (and small hole before the mid-box!),
she said 'wowww what did you do? It's much faster and smoother. I love it!'

Not bad considering my first time tuning a carb!!
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

Just an update guys.

Had a nice new exhaust system fitted (mid and rear, also with a thread for a lambda that I purchased so I can monitor the AFR), not all SS but good quality galvanized. Exhaust tip is SS.

Sounds great, not loud but nice and raspy! The fitter had done many 33's before and knew what was good for it.

Also fitted '53' idle jets (0.01mm up from the factory size). Great improvement I must say. Maybe due to the slight increase in air intake with the K&N air filter?

Now I've just got to fix the wipers. I'm thinking the right linkage is slightly bent. I have removed the right (passengers side) wiper to take off the strain for the moment.







[/b]
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Brit01]

Early xmas present!!

Finally got a Bosch wideband lambda kit and gauge installed on my new exhaust system.

Nice piece of kit and cool to see the AFR as you are driving and a piece of cake to set the idling and see the jets as you are cruising.

Idling I found a good point is about 13.1. Anything above 14 and the engine gets a bit too hot and revs drop (too lean).

140km @ 4000rpm ranges 13.1-13.8.
idle jets up to 3000 rpm ranges around 12.5 (great torque here)


[url]

Uploaded with ImageShack.us[/url]
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S2 33 1988 1.7 QV
Dellorto DRLA40 (32mm venturi)

[Joelomint]

Just a thought, so i hope i'm not opening a tin of worms for you.. but think you mention the idle suffering after braking/decelleration? I have had this problem on a couple of the 33s i've owned, and the biggest single improvement came from resetting and/or renewing the floats.. the floats become less 'floaty' over time, and can allow excess fuel into the carbs - especially when braking!

Just a thought tho, but if you are gonna strip the carbs down at some point, definately check the function of the floats..

[Brit01]

Runs like a dream now.
Better than ever before. Torque is superb, especially after I extended the main air intake a little.

Carbs reconditioned and polished. New float valves but the floats could do with changing. That will be a special shipping task as they are not available here.

[Brit01]

photo of my newly conditioned carbs: (ignore the cold air intakes, these have now been modified to fit correctly)

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