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Discussion Starter · #1 ·
Hi

I am new to carb and could use some expert advice.

Got a AFR500v2 AFR unit from Ballenger installed it with its supplied wideband sensor last night and took the car for a ride.
This is a US 2L 1976 Alftetta with newly installed a pair of Weber DCOE32.
The car is equipped with 123 Bluetooth ignition, euro intake manifold and euro exhaust manifold.

I validated the Weber to be per original spec:

Main Venturi: 32
Emulsion tube: F9
Main Jet: 130
Main Air: Corrector: 200


Now for the AFR results:

After full warm up idle AFR is 14~15.
When accelerating numbers move toward 12~13 until the main circuit kicks in at around 3000 RPM where the number changes to around 11 and stays this way up to max RPM.
Car ideal nice and I don鈥檛 feel any week spots upon acceleration.

Logic says I need to increase the air corrector size a bit, say from 200 to 210 in order to get to the optimal power ratio of 12.5, am I correct?

According to all the Weber DCOE Jet guides the Air corrector needs to bigger from the main fuel jet by 50, so why are Alfa Engine don鈥檛 follow these rules?

For fuel delivery I use a low-pressure electric pump with a measured stable output pressure of 4PSI, I know that this is a little bit over the ideal which is 3.5PSI, can that somehow affect the AFR? Is a 4PSI really too much for Webers?

Thanks for your help 馃檹

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Richard Jemison
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Are your readings at full throttle acceleration, in which case going to a 210 air corrector should help resolve the high RPM readings. But higher fuel levels could be the issue.
But what are the readings at normal street driving, and no load cruising?
If you are measuring fuel pressure at the carbs the high fuel pressure is probably effecting the fuel level. which does cause a richer mixture if too high.
Commonly the range below works well.
Idle: 14-16
Off idle acceleration: 11 to 12 as accelerator jet is influencing mixtures
2000 to 3500 steady state cruising: 12.5 to 14
4000 to 6000 full acceleration: 12 to 13.5
3500- 5000 steady state cruising: 13 to 14
 

But Mad North-Northwest
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Also bear in mind that carburetors are basically controlled fuel leaks. They're clever and they work, but they have limited ability to compensate for changing conditions.

So if you have an AFR meter it's worth tweaking them, but don't chase perfection: get them close enough and then call it good.
 

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yes 4psi is enough to push past the float valve, not alot but enough to actualy over fuel, now mind you it may or may not be happening right now with a "new" needle and seat but once its worn in id be suprised if it didnt over fuel by a little bit, 3.5 is really considered "maximum pressure" for carbs in general as anything more is enough to push past the needle/valve atleast a little bit....ive even seen where webbers dont like anything over 3psi, so do yourself a favor and put a regulator inline
 

But Mad North-Northwest
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Yeah, I'm with Shortlife on the pressure thing.

Having been through a few iterations, what has worked best and most consistently for me with carbs is this:
  • Facet Gold Flo low pressure pump as close to the tank as possible. Mount it vertically and do not install a filter between the tank and pump
  • Filter King filter/regulator (glass bowl version, not plastic!) in the engine bay set to the stock 3 PSI


I also like to install this inertia switch on the pump power feed for safety, but that's up to you:

 

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fwiw the inertai switch can be used off of any of the late 90s and newwer crown vics if you want to cut costs and use a "off the shelf" part

that filter unit is down right sexy, i wish something like that could be used with FULL FI pressures...nothing better than being able to SEE how dirty your fuel is
 

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Discussion Starter · #8 ·
Hello frinds

Richard,
If the rich mixture Is caused by the high fuel preasure i will attend this before moving fwd.

Looking at the expected AFR numbers you provided I'd say my idle and transaction is more or less OK and it's when main kicks in the number drops.
For more accurate figures I will have to take a friend for a test drive and let him video the gauges while accelerating.

Gubi, ShOrtLife
I understand what you are saying I can easily go into a never ending loop of playing with these.
The pump is a basic, suppose to be 2-3.5 PSI regulated type I bought from amazon (Carbole).
I have the main fuel filter next to it and another small generic plastic case type filter near the carburetors.

The Facet and filter king looks nice but I thought I'll try to manage without these relatively expensive ones and try a simpler "regulated" pump.

I kept the inertia safety fuel switch from the spica setup, i rebuilt it and it works fine.

Update: took the fuel hose out of the carb and noticed the fuel preasure on the gauge is not dropping to zero.
This is strange as this gauge used to work fine.
The gauge has a Calibration screw so I zeroed it and plugged everything back.
The preasure readings is now a steady 3.8PSI.

See below some pic of my setup.
Again thank you all for sharing your wisdom.

Samuel
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But Mad North-Northwest
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The Facet and filter king looks nice but I thought I'll try to manage without these relatively expensive ones and try a simpler "regulated" pump.
I get it, I've used a few cheaper solutions myself. But the setup I described above is pretty bulletproof.

"Buy once, cry once" is a lesson the Alfas have taught me on more than one occasion.
 

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Air correctors mainly influence AFR at WOT and they have a much smaller influence at part throttle. If the AFR is in the 11's when cruising at 70 - 80 mph then you should try 125 main jet. If it is in the 12's and 13's in that cruising range then 130 is correct. Then do WOT runs. The AFR should be in 12 - 13.5 range at high rpm. That can be adjusted by changing the air correctors. Fuel pressure can change fuel height which in turn affects AFR. RJ recently fixed an AFR problem on his race car by adjusting the fuel height by 1 mm.
 
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Discussion Starter · #11 · (Edited)
Update; Ordered a fuel pressure regulator, until it arrives, I reduced the fuel pressure by lowering the Fuel pump operating voltage (4 high current Silicon diode connected in series), I now have a steady 3.1 PSI.

Also tweaked the idle mixture a bit (slightly leaner) and took the car for a ride

The idle AFR when the car is fully warm standing is around 15, Idle RPM is around 750.

Full throttle acceleration from idle to 4000RPM is around 12, from 4000 to 6300 it goes down to 11.5.

Cruising at 3000RPM on fifth gear AFR is around 13.

All these values are +/- 0.3 as the numbers jump on the AFR display and you have to average them In your brain Also when throttle position changes there is sometime a delay until numbers stabilize.


Driving the car, compared to the spica the carb replaced not a huge difference.
With the new installed carb鈥檚 the engine starts better and goes higher in RPM.
I think the tourqe improved but I鈥檓 not sure about it as the feel is different.
The spica was definitely more civilized in the way it climbed in RPM almost as the rate was controlled.

Ordered a 210 Air corrector and might also try a 125 main, I鈥檓 close, its just fine-tuning that is needed.
My target numbers are the one Richard suggested.

I have a friend with a 2Liter MK3 spider equipped with original Euro Carb Nord engine, this is my stock euro benchmark.
His car (based on my memory) is more agile and willing to climb in RPM faster, the only difference between this and my car is the Camshaft, the Spider has the 105480 type cam and my Alfetta is still with the SPICA emission cams.
Another possible reason for the more nimble feel may be the weight diffrence between the two cars.


Thx
Samuel.
 

Richard Jemison
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What lobe centers do you have the Spica cams installed at. Spica was about emission control, nor power.
Changine loce centers can have a big positive (or negative) effect on engine performance.

The Spica cams were the worst used on Alfa engines, and only in the USA. The 10548-01 cams were street application for ROW engines.
 

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Discussion Starter · #13 · (Edited)
What lobe centers do you have the Spica cams installed at. Spica was about emission control, nor power.
Changine loce centers can have a big positive (or negative) effect on engine performance.

The Spica cams were the worst used on Alfa engines, and only in the USA. The 10548-01 cams were street application for ROW engines.
Thank you Richard

They are set standard, 102 for both intake and exhaust.
Can I produce more power by setting them differently?

I have a single used 10548 cam on the shelf with no visible lobe ware, (smooth, round and same height) found it on a junkyard with some rust spots which I cleaned using WD (no sanding or anything like that).
It's still doesn't look great which is why i did not want to install it as i was afraid that the coating may be damaged and didn't want ruin my tappet, what do you think?

if i do the swap to what lobe center should i set the intake 105480 and exhaust spica.
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Richard Jemison
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Does look bad, but I would suggest using Aluminum wheel cleaner (acid comes in a spray can) and spray the cam with it leaving it wet for at least 1 hour. (Get the oil off of it first) It will remove the rust. in the pitted areas. If after that you can feel divots/holes then it`s useless for anything not even a core as the bearing area has to be smooth as does the lobes.
With the little stock cams I suggest advancing the intake cam to a lobe center of 99 degrees (1 hole on the sprocket. and on the exhaust side retard the LC to 99 degree LC. another 1 hole movement.

These (99 degree LCs) were the stock 10548 specs and there is no way these cams will have piston to valve interference at those settings. Should result in a torque boost.
 

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Discussion Starter · #15 ·
Does look bad, but I would suggest using Aluminum wheel cleaner (acid comes in a spray can) and spray the cam with it leaving it wet for at least 1 hour. (Get the oil off of it first) It will remove the rust. in the pitted areas. If after that you can feel divots/holes then it`s useless for anything not even a core as the bearing area has to be smooth as does the lobes.
With the little stock cams I suggest advancing the intake cam to a lobe center of 99 degrees (1 hole on the sprocket. and on the exhaust side retard the LC to 99 degree LC. another 1 hole movement.

These (99 degree LCs) were the stock 10548 specs and there is no way these cams will have piston to valve interference at those settings. Should result in a torque boost.
Hi Richard

Thank you for all the tip's, I was out of my house for the last few days but will try cleaning it as you suggested.
One last question (sorry for being that pedantic):

What would give better results, a pair of 105480 cams set both to 99掳 (euro standard) or,, a mix of 105480 on Intake and US Spica cam on exhaust set both to 99掳?

if mine is good I may opt for buying another one locally and install a pure pair.


Thank you
Samuel.
 

Richard Jemison
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Either cam setup will result in too much overlap that kills low end torque, and that lost fuel air mix reduces the volumn of fuel air in the compression stroke another power reducer.
Whichever cam you use set the exhaust cam at .021" lash to reduce early duration off the seat and reduce overlap.
 

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Discussion Starter · #17 ·
Hello Doctor Jemison

See attached recent pictures of the single 105480 cam I have, I cleaned it the way you suggested and its still has some stain on it though it doesn't look like they go deep.

To the garbage or can it be used?

Thank you Sir.

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Replace or have the cams repaired. Those cams are done, however you can now buy new cams and cam followers...maybe even get a better performance cam as well. Also with the cams comes valve adjut as well. Good luck
 
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