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carburetor [fiat] explaination x2
FIAT
Special to mirafiori
Tuning Single Carburetors
Preliminary Settings
Note: These is the recommended procedure per Weber with some modifications, you will find the same general steps in any publication on setting up carburetors.
Check Factory Settings
Do not rely on the factory settings unless otherwise directed by your vendor. Back out the idle speed screw (see figure) until it is no longer in contact with the throttle stop lever. Now turn the screw until it contacts the lever and again 1 ½ turns. Turn the idle mixture screw (on our carburetors it is typically in the center bottom of the carburetor body) in until it is fully seated - do not force the screw. Now turn it back out two full turns.
Start and warm the Engine
Disengage or block the choke open. On automatic chokes you can use a small clamp or wire to pull the choke mechanism open. The engine should start and run poorly (if it does not then increase the idle speed screw ½ turn until it does). Adjust the idle speed screw until the engine runs at approximately 900 RPM. Turn the mixture screw in (lean the mixture). If the engine increases in speed then continue to turn until it is no longer increasing or runs worse, then back the screw out ½ turn. If the engine decreases in speed then turn the screw out until it is increasing in speed. Continue to turn until it is no longer increasing or runs worse, then turn the screw in ½ turn. Adjust the idle to approximately 850 RPM. Let the engine warm up to operational temperature. On a Spider you will wait until the fan has cycled two times (on-off-on-off).
Final Settings
Note: should the engine fan come on during these steps STOP working until it shuts off. Set the idle speed screw so that the engine runs at 850 RPM, or 900 RPM if you have air conditioning. Recheck the mixture screw by turning slightly in then out. Engine speed should be set - using the mixture screw ONLY - to the fastest and smoothest point of operation (listen for exhaust popping). Reset the idle speed screw as necessary.
.bmp)
The Mystique
Dual Webers are just plain neat to work on, look at, and operate. They are loud, powerful, and demonstrate your ability to really tackle carburetion. Many FIAT owners consider installing twin Webers on their FIAT engine, and many have taken the plunge.
Dual Carburetor Configurations
There are configurations that you should consider if you want to work with twin carburetors. They are both Weber products, Solex and Dellorto configurations are not listed because they are not available new and parts can be nearly impossible to find. These carburetors are downdraft, two-barrel, synchronous operating units. Each barrel is fully independent of the other and can be tuned as such. Barrels share only the fuel bowl and accelerator pump. They require special manifolds to work - manifolds without plenums, so each cylinder has a unique runner to its own carburetor barrel. The two models used on FIATs are the Weber IDF and DCNF. The Weber IDF is available in 40, 44, and 48mm configurations.
.bmp)
Dual Carburetors
The second popular configuration is the Weber DCNF, available in 40 and 44mm sizes. The 40DCNF is a more compact and modern design, but the operational principles are the same as the IDF. Generally speaking, a set of DCNFs will cost more because the manifolds are a bit more expensive. However, the manifolds are also a bit higher in quality and design than the IDF manifolds. Ultimately, the choice is yours. FIAT used IDFs so many people choose those. I have used both and have been very pleased with them.
How much power will I get?
About 25% more than a stock single carb, which is very restrictive. You are literally doubling the venture area when you go to dual carbs over stock. Compared to fuel injection, the picture is muddier, since stock specs show that FI adds 20% to the twin cam.
Are they hard to keep in tune?
Opinions vary - Mike Richmond (who wrote the majority of this appendix) says Not if you stick with a “tried and true formula: set them up and tune them. Then leave them alone. Replace the needle/seat and clean them every 24,000 miles.” My experience has been that they are generally seasonal, at least in Atlanta I found myself jetting up or down (just the idle jets, mind you) four times a year. Easy work.
Are they hard to tune the first time?
They shouldn’t be, but most people make the mistake of failing to install them right the first time (especially used ones) or they change too many things at once. Install them right and be scientific and you will have them humming after a couple of weekends. In the meantime, you will learn to curse in Italian. You absolutely need a device to measure the amount of air drawn into the carburetor barrels (available from most vendors or carburetor shops) to tune these carburetors correctly. This device measures the amount of airflow into each barrel. The preferred unit is the Type SK (vs. the Type BK) Synchrometer with adapter number 18. This will fit nicely into the ram pipes (velocity stacks) of the IDF 13/15s. The Uni- Syn gauge (another type of metering device) is not recommended for tuning IDFs. A fourth type is available from most motorcycle shops and has four gauges which each attach to the vacuum port at the base each carburetor (next to the air bleed screw). I refer to ALL of these devices as in the next topic.
Quick Tuning Guide
First, reset the carburetor to its basic settings. Turn in all four air bleed screws until they are seated. Screw in all four mixture screws until they seat, then back out 1 ½ turns. Adjust the idle stop screw (between the carburetors) so that the engine idles (even if poorly) around 900 RPM. Balance the airflow between barrels using the synchrometer. First measure the air in both barrels of a single carburetor. Adjust the one with the lowest reading to match the one with the highest reading by adjusting the air bleed screw. Repeat for the other carburetor. Now compare the airflow on one carburetor to the other and balance them using the center link balancing screw. Set the mixture by turning the mixture screws - one at a time. First turn the screw in, if the engine speed begins to increase keep turning until the speed begins to decrease or run worse then back ½ turn. If the engine speed begins to decrease reverse this operation, turn the screw out and speed will increase, turn until it begins to decrease or run worse then in ½ turn. Fine tune as necessary using similar steps. These are finesse carburetors, you master them in a very short amount of time!
# if you to get FIAT WEBER carburetor manual click this: FIAT WEBER MANUAL
carburetor [fiat] explaination x2
FIAT
Special to mirafiori
Tuning Single Carburetors
Preliminary Settings
Note: These is the recommended procedure per Weber with some modifications, you will find the same general steps in any publication on setting up carburetors.
Check Factory Settings
Do not rely on the factory settings unless otherwise directed by your vendor. Back out the idle speed screw (see figure) until it is no longer in contact with the throttle stop lever. Now turn the screw until it contacts the lever and again 1 ½ turns. Turn the idle mixture screw (on our carburetors it is typically in the center bottom of the carburetor body) in until it is fully seated - do not force the screw. Now turn it back out two full turns.
Start and warm the Engine
Disengage or block the choke open. On automatic chokes you can use a small clamp or wire to pull the choke mechanism open. The engine should start and run poorly (if it does not then increase the idle speed screw ½ turn until it does). Adjust the idle speed screw until the engine runs at approximately 900 RPM. Turn the mixture screw in (lean the mixture). If the engine increases in speed then continue to turn until it is no longer increasing or runs worse, then back the screw out ½ turn. If the engine decreases in speed then turn the screw out until it is increasing in speed. Continue to turn until it is no longer increasing or runs worse, then turn the screw in ½ turn. Adjust the idle to approximately 850 RPM. Let the engine warm up to operational temperature. On a Spider you will wait until the fan has cycled two times (on-off-on-off).
Final Settings
Note: should the engine fan come on during these steps STOP working until it shuts off. Set the idle speed screw so that the engine runs at 850 RPM, or 900 RPM if you have air conditioning. Recheck the mixture screw by turning slightly in then out. Engine speed should be set - using the mixture screw ONLY - to the fastest and smoothest point of operation (listen for exhaust popping). Reset the idle speed screw as necessary.
.bmp)
The Mystique
Dual Webers are just plain neat to work on, look at, and operate. They are loud, powerful, and demonstrate your ability to really tackle carburetion. Many FIAT owners consider installing twin Webers on their FIAT engine, and many have taken the plunge.
Dual Carburetor Configurations
There are configurations that you should consider if you want to work with twin carburetors. They are both Weber products, Solex and Dellorto configurations are not listed because they are not available new and parts can be nearly impossible to find. These carburetors are downdraft, two-barrel, synchronous operating units. Each barrel is fully independent of the other and can be tuned as such. Barrels share only the fuel bowl and accelerator pump. They require special manifolds to work - manifolds without plenums, so each cylinder has a unique runner to its own carburetor barrel. The two models used on FIATs are the Weber IDF and DCNF. The Weber IDF is available in 40, 44, and 48mm configurations.
.bmp)
Dual Carburetors
The second popular configuration is the Weber DCNF, available in 40 and 44mm sizes. The 40DCNF is a more compact and modern design, but the operational principles are the same as the IDF. Generally speaking, a set of DCNFs will cost more because the manifolds are a bit more expensive. However, the manifolds are also a bit higher in quality and design than the IDF manifolds. Ultimately, the choice is yours. FIAT used IDFs so many people choose those. I have used both and have been very pleased with them.
How much power will I get?
About 25% more than a stock single carb, which is very restrictive. You are literally doubling the venture area when you go to dual carbs over stock. Compared to fuel injection, the picture is muddier, since stock specs show that FI adds 20% to the twin cam.
Are they hard to keep in tune?
Opinions vary - Mike Richmond (who wrote the majority of this appendix) says Not if you stick with a “tried and true formula: set them up and tune them. Then leave them alone. Replace the needle/seat and clean them every 24,000 miles.” My experience has been that they are generally seasonal, at least in Atlanta I found myself jetting up or down (just the idle jets, mind you) four times a year. Easy work.
Are they hard to tune the first time?
They shouldn’t be, but most people make the mistake of failing to install them right the first time (especially used ones) or they change too many things at once. Install them right and be scientific and you will have them humming after a couple of weekends. In the meantime, you will learn to curse in Italian. You absolutely need a device to measure the amount of air drawn into the carburetor barrels (available from most vendors or carburetor shops) to tune these carburetors correctly. This device measures the amount of airflow into each barrel. The preferred unit is the Type SK (vs. the Type BK) Synchrometer with adapter number 18. This will fit nicely into the ram pipes (velocity stacks) of the IDF 13/15s. The Uni- Syn gauge (another type of metering device) is not recommended for tuning IDFs. A fourth type is available from most motorcycle shops and has four gauges which each attach to the vacuum port at the base each carburetor (next to the air bleed screw). I refer to ALL of these devices as in the next topic.
Quick Tuning Guide
First, reset the carburetor to its basic settings. Turn in all four air bleed screws until they are seated. Screw in all four mixture screws until they seat, then back out 1 ½ turns. Adjust the idle stop screw (between the carburetors) so that the engine idles (even if poorly) around 900 RPM. Balance the airflow between barrels using the synchrometer. First measure the air in both barrels of a single carburetor. Adjust the one with the lowest reading to match the one with the highest reading by adjusting the air bleed screw. Repeat for the other carburetor. Now compare the airflow on one carburetor to the other and balance them using the center link balancing screw. Set the mixture by turning the mixture screws - one at a time. First turn the screw in, if the engine speed begins to increase keep turning until the speed begins to decrease or run worse then back ½ turn. If the engine speed begins to decrease reverse this operation, turn the screw out and speed will increase, turn until it begins to decrease or run worse then in ½ turn. Fine tune as necessary using similar steps. These are finesse carburetors, you master them in a very short amount of time!
# if you to get FIAT WEBER carburetor manual click this: FIAT WEBER MANUAL
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