CARBURATORS:
Before we proceed lets make one thing clear so as not to confuse ourselves. CARBS DONT SUCK FUEL!,VACUUM PULLS THE FUEL!,or the famous of all! 'THIS THING SUCKS A LOT OF AIR'!!!
To keep us in line and to be precise,the correct definition is ATMOSPHERIC PRESSURE! pushes the fuel in to the carburetor. Vacuum also is a misnomer as it is the ABSENCE OF PRESSURE that is incorrectly defined as vacuum...
Carbs is as ancient as the engine itself. The most meaningful improvement from the start of time is the power valves and the vacuum or mechanical secondaries. Other types have needle jets like the Mikunis and replaceable air jets and changeable venturi's.
We will try to keep it simple here and just generalize instead of pointing the different systems of idle,mid range and power circuits on this different types. One thing comes in clear to the engine tuner!
THE SPARK PLUG IS YOUR PARTNER! I do not know if i can properly get the carb to function correctly with out taking a look at the color or the proper heat range of the plugs. BEWARE! not all spark plug will show combustion color,some are self cleaning and if the plug is too cold it shows like its running 'rich'. If its too hot it shows too 'lean'. Know this and its a TUNERS SECRET WEAPON! I have seen engines where the carb is blamed as 'junk' when the plugs are not read properly and the jetting and all else including timing is wrong....
The sharp builder has a distinct edge when he uses all the tools at his disposal to put distance between him and the competition!
Follow the Manufacturers recommendation as to the proper CFM rating. deviate away from this only! when you have a very radical engine capable of extreme RPMs and or compression ratios and cam timing that seem like this thing would or should not even run....This are the engine builders that balances extreme cam timing and multiple carburetors with unbelievable compression ratios way past 15.1!
How do you know your carburetor is size correctly?
I will give you a 'hint' that worked for me. Beside my Tach is my trusty 'Vacuum' Gauge.( Again the wrong description but for the sake of argument we will call it this).
At FULL THROTTLE AND TOP GEAR! before you let off on the next turn or crossing the finish line at the strip, note your vacuum readings!
if it is close to ZERO! Your induction is too BIG! If it has too MUCH Vacuum reading at full throttle! it is TOO SMALL! size accordingly! Beware that when you have a very restrictive exhaust with a lot of BACK PRESSURE the reading will also affect this...because if it cannot exhaust out, it will not ingest on the intake!!!
Another tip! On the dyno or at the track.
When you see a lot of FUEL RESIDUE from the area ABOVE THE VENTURI! ("'vena contracta" is the latin word for this constriction or venturii).
You have REVERSION!
The intake is coming back out to the carb! This is evident on FULL THROTTLE as a MIST or CLOUD on the TOP of the carb or!
What caused this?
1. just make sure its is not residue from the accelerator pump, 2.The Manifold is too short and the intake is pulsing back out to the carb or, from the sudden rush of air/fuel colliding with the just abruptly closed intake valve...this wave of mixture will bounce back to the carb and beyond..
3. The Venturi (size) is too big and the velocity thru the venturi is slow and the subsequent back-flow will occur.
4. A combination of #2 and 3 usually will exhibit a Carburetor "GROWL" or WOOSHING SOUND or what we call" CRASHING or ROAR".
When you accelerate and most of all evident on the lower or mid RPMs. What is probably ideal is the sound of rapid air being ingested at a high rate when the car accelerates...
You ever notice that when this GROWL is heard the car seem to labor or sluggish and just will not build or accelerate fast to higher RPMs or gain speed ?
Run a Velocity stack or any kind of air straightener to the venturi. even a filter will usually help as long as it is not restrictive. Make sure there are no air movement across the carb inlet at speed.this will throw the carb off as a disturbance above the venturi will affect its performance and metering...
Isolate your carbs with an" air pan or air box". if you can seal this and utilize a Ram-Air from the grille or the high pressure at the base of the windshield, do so as this is free horsepower!
Utilize a COOL CAN if possible! the chilled or cooler fuel will improve combustion as it is denser when its cold.( cooler or denser fuel carries more weight and helps prevent detonation and the formation of "vapor Lock".) I have seen a tenth reduction and up to almost 2 mph in the quarter. thats Free Horsepower!!!
And dont forget to make sure your air bleeds,venturi and even your idle circuit are clean.( in some carbs the idle circuit also functions as a reverse air bleed).
Also the often overlook part of a carb set-up:
FUEL PUMP VOLUME / PRESSURE.
You can have all the top line Pumps and Regulators and it would still be inadequate!
Example: I installed a so called race pump to support a lot of HP! my fuel requirements called for a Gallon in 18 seconds! this "Trick Pump"
made a gallon in 28 seconds...I had to run two regulators and had to modify the junction from the two pumps.
LESSON TO BE LEARNED?
FLOW TEST YOUR FUEL SYSTEM AT THE CARB INLET TO VERIFY THAT IT CAN AND WILL DELIVER THE REQUIRED DEMANDS OF YOUR ENGINE....
Regardless of who manufactured the pumps!!!
Fuel line routing,Alternator output and Battery condition affects this results.
On some total loss systems we run dual batteries or dual 16 VOLT BATTERIES! THIS OVERDRIVES THE FUEL PUMPS.ELECTRIC WATER PUMP AND IGNITION SYSTEMS.....
BEN ALAMEDA @ PARA, FB, BENALAMEDARACING.COM
( tech. articles in memory of Chuck Stevens: Mentor & Friend )
Before we proceed lets make one thing clear so as not to confuse ourselves. CARBS DONT SUCK FUEL!,VACUUM PULLS THE FUEL!,or the famous of all! 'THIS THING SUCKS A LOT OF AIR'!!!
To keep us in line and to be precise,the correct definition is ATMOSPHERIC PRESSURE! pushes the fuel in to the carburetor. Vacuum also is a misnomer as it is the ABSENCE OF PRESSURE that is incorrectly defined as vacuum...
Carbs is as ancient as the engine itself. The most meaningful improvement from the start of time is the power valves and the vacuum or mechanical secondaries. Other types have needle jets like the Mikunis and replaceable air jets and changeable venturi's.
We will try to keep it simple here and just generalize instead of pointing the different systems of idle,mid range and power circuits on this different types. One thing comes in clear to the engine tuner!
THE SPARK PLUG IS YOUR PARTNER! I do not know if i can properly get the carb to function correctly with out taking a look at the color or the proper heat range of the plugs. BEWARE! not all spark plug will show combustion color,some are self cleaning and if the plug is too cold it shows like its running 'rich'. If its too hot it shows too 'lean'. Know this and its a TUNERS SECRET WEAPON! I have seen engines where the carb is blamed as 'junk' when the plugs are not read properly and the jetting and all else including timing is wrong....
The sharp builder has a distinct edge when he uses all the tools at his disposal to put distance between him and the competition!
Follow the Manufacturers recommendation as to the proper CFM rating. deviate away from this only! when you have a very radical engine capable of extreme RPMs and or compression ratios and cam timing that seem like this thing would or should not even run....This are the engine builders that balances extreme cam timing and multiple carburetors with unbelievable compression ratios way past 15.1!
How do you know your carburetor is size correctly?
I will give you a 'hint' that worked for me. Beside my Tach is my trusty 'Vacuum' Gauge.( Again the wrong description but for the sake of argument we will call it this).
At FULL THROTTLE AND TOP GEAR! before you let off on the next turn or crossing the finish line at the strip, note your vacuum readings!
if it is close to ZERO! Your induction is too BIG! If it has too MUCH Vacuum reading at full throttle! it is TOO SMALL! size accordingly! Beware that when you have a very restrictive exhaust with a lot of BACK PRESSURE the reading will also affect this...because if it cannot exhaust out, it will not ingest on the intake!!!
Another tip! On the dyno or at the track.
When you see a lot of FUEL RESIDUE from the area ABOVE THE VENTURI! ("'vena contracta" is the latin word for this constriction or venturii).
You have REVERSION!
The intake is coming back out to the carb! This is evident on FULL THROTTLE as a MIST or CLOUD on the TOP of the carb or!
What caused this?
1. just make sure its is not residue from the accelerator pump, 2.The Manifold is too short and the intake is pulsing back out to the carb or, from the sudden rush of air/fuel colliding with the just abruptly closed intake valve...this wave of mixture will bounce back to the carb and beyond..
3. The Venturi (size) is too big and the velocity thru the venturi is slow and the subsequent back-flow will occur.
4. A combination of #2 and 3 usually will exhibit a Carburetor "GROWL" or WOOSHING SOUND or what we call" CRASHING or ROAR".
When you accelerate and most of all evident on the lower or mid RPMs. What is probably ideal is the sound of rapid air being ingested at a high rate when the car accelerates...
You ever notice that when this GROWL is heard the car seem to labor or sluggish and just will not build or accelerate fast to higher RPMs or gain speed ?
Run a Velocity stack or any kind of air straightener to the venturi. even a filter will usually help as long as it is not restrictive. Make sure there are no air movement across the carb inlet at speed.this will throw the carb off as a disturbance above the venturi will affect its performance and metering...
Isolate your carbs with an" air pan or air box". if you can seal this and utilize a Ram-Air from the grille or the high pressure at the base of the windshield, do so as this is free horsepower!
Utilize a COOL CAN if possible! the chilled or cooler fuel will improve combustion as it is denser when its cold.( cooler or denser fuel carries more weight and helps prevent detonation and the formation of "vapor Lock".) I have seen a tenth reduction and up to almost 2 mph in the quarter. thats Free Horsepower!!!
And dont forget to make sure your air bleeds,venturi and even your idle circuit are clean.( in some carbs the idle circuit also functions as a reverse air bleed).
Also the often overlook part of a carb set-up:
FUEL PUMP VOLUME / PRESSURE.
You can have all the top line Pumps and Regulators and it would still be inadequate!
Example: I installed a so called race pump to support a lot of HP! my fuel requirements called for a Gallon in 18 seconds! this "Trick Pump"
made a gallon in 28 seconds...I had to run two regulators and had to modify the junction from the two pumps.
LESSON TO BE LEARNED?
FLOW TEST YOUR FUEL SYSTEM AT THE CARB INLET TO VERIFY THAT IT CAN AND WILL DELIVER THE REQUIRED DEMANDS OF YOUR ENGINE....
Regardless of who manufactured the pumps!!!
Fuel line routing,Alternator output and Battery condition affects this results.
On some total loss systems we run dual batteries or dual 16 VOLT BATTERIES! THIS OVERDRIVES THE FUEL PUMPS.ELECTRIC WATER PUMP AND IGNITION SYSTEMS.....
BEN ALAMEDA @ PARA, FB, BENALAMEDARACING.COM
( tech. articles in memory of Chuck Stevens: Mentor & Friend )
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