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My 1983 Spider Veloce 1.6 has a problem of hesitation/stumble on acceleration, when the pedal is pushed hard and this occurs at less than 3,500 RPM starting at around 1800 rpm. If I press the acceleration pedal very slow, the issue is not there.

My car has Weber 40 DCOEs 106 and 107A with the following jets:
1) 55 F 21 jets for idle
2) F41 for emulsion tube + 132 main jets
3) 30 acceleration pump jets
4) 85 F 9 starter jet air jet start 150

Since idle is set at more than 1 & 1/2 turns from sitting (max recommended) it means the car runs with a lean idle mixture that is compensated by the tuning the idle mixture screw to enrich the mixture. I think I should try 60 F9 jets to compensate for being too lean. At alfa BB someone reported moving from 55F21 to 55F17 one step richer might be sufficient. Des Hammill (his book on Weber and Dellorto build and tne is must read) recommends go up (richer) with idle jet size at 5 increments like 60, 65 and 70 if idle screws need to be turned on more than 1 1/2.. mine is about 10 turns !

Other suggestions for the issue, I read for flat spot in acceleration (up through 3500 RPM) tbd (to be determined) besides Idle jets too small are:
1) Progression air correction jets too large->right now mine is the minimum at 30 so I am not sure. But Redline Fuel Management suggest to go to a 55 jet for the acceleration pump to increase duration and increase fuel volume. Also Des suggest that "acceleration jets should be large enough to remove any trace of hesitation or stumbling when the accelerator pedal is depress"
2) Floats set too low->checked to 8.5 mm at jet closed and 15 mm total drop per spec, still an issue after calibration to spec for my 40 DCOE Weber (also changed the needle valve jets with the new ones of the Redline kit)
3) Try adjusting mixtures at 1800 to 2000 RPM-> this won't work as you compensate the lean idle by acting on the mixture and make the engine running rich with not completing combustion
4) Exhaust header too big->to check with spec as it was replaced in my car by previous owner
5) Valve clearance set too tight (advances timing)-> to check
6) Ignition over-advanced-> to check
7) Weak spark->changed spark plugs, still an issue after change (btw spark plugs are somehow black means the engine run rich mixture by previous owner)
8) Check the fuel squirt of the progression pump when pressed in each carburetor and the stroke length (11 mm)-> to check
9) Check the throttle position at idle below the progression holes-> to check Note Redline fuel management says that this is 95% of tuning problem cause as the the throttle plate when the the idle screw is more than 1 an 1/2 turn (like my case) is exposing (means already using at idle instead during the progression) the progression holes causing to start the engine to stumble off idle at 1800 rpm
10) Check or replace the emulsion tubes-> to check
11) Check the fuel level in the carb bowls -> to check

Anybody in the forum had a similar issue with their Alfa with Weber 40 DCOE and solved the root cause of the issue?
 

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you are in the states with a 1983 1.6 liter spider????? i thought they are were 2.0 liter cars.. and after 1981 they all came with bosch fuel injection,,,did you remove your fuel injection?
 

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you are in the states with a 1983 1.6 liter spider????? i thought they are were 2.0 liter cars.. and after 1981 they all came with bosch fuel injection,,,did you remove your fuel injection?
My thoughts exactly but might be a gray market car. That is all that I can figure
 

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You should swap in Ljet fuel injection, it would get rid of all those nasty carb problems..........
 

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Nice checkiist. Thanks, I'll be needing a starting point once I mount the new airbox and Shankle headers.
However, I'm not help with your problem.

BTW, I also have Webers on my originally-SPICA 1972 Spider (but a 2000cc with 45DCOE's). I am a firm believer in fuel injection, and I contemplated converting to FI, but the costs and time to convert are not worth the effort.
 

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carbs are better.carbs give you big hp,,,lol
 

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always wondered..if carbs are great for race cars.. why dont they use them ? all the ones i have seen are F.I.
 

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Bianchi, you have done interesting things with you car and I appreciate the information you have contributed over the years. However, your constant carburetor "beat-down" grows old particularly when it is irrelevant to the subject at hand. How about appreciating both FI and carbs for their merits and let it go?

To the OP, you mention a stumble or hesitation as low as 1800 rpm. That could certainly be carburetor related but it could also be the result of an ignition problem. I would make sure the ignition system is in good shape before focusing on the Webers. For that matter, if the car is new to you, perhaps consider going through the normal maintenance checks such as compression, valve clearances, valve timing, timing chain tension, distributor cap, rotor, points/condenser if you have them, coil/spark plug wires, ignition timing, etc. Eliminate as many variables as you can to be more confident that the problem is indeed related to carburetion.

You may know the DCOE 106/107s are "emissions" Webers. They will work fine when properly setup but there are physical differences as well as tuning differences between "classic" Webers and "emissions" Webers. You need to be aware these differences exist when consulting reference documentation. Settings that work for one series of Webers may not be appropriate for the other. With that out of the way, I would not start swapping idle jets yet. The jets you have are about right for a 2L engine and should be adequate if not too large for a 1.6L. I would check carburetor synchronization as a first step after confirming that the problem is not originating elsewhere.
 
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