Securanoia

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-# Carbeurators
+# Carburetors
 ** Just Holley 4150 & 4160 for now **
 **Note:** If non-ethanol compatible materials are used for the needle-and-seats' O-rings or for the accelerator pumps' diaphragms they could be damaged by ethanol gasoline
+- If the car is lean or rich during normal driving conditions, you need to tune the jets, not the power valve
+- A competition or race engine which has a long duration high overlap camshaft will have low manifold vacuum at idle speeds.
+- Before adjusting the carb's jets, or valves
+	- eliminate any possible issues with the vehicle's ignition
+	- eliminate any possible issues with the vehicle's fuel system
+	- Verify the damper and timing tab really do reflect TDC
+	- Verify the ignition advance is working correctly
+	- Verify you have 5 psi of steady fuel pressure at the carb
+	- Verify the carb's floats are set correctly
+	- Verify that the cars valves are adjusted (valve lash?)
+	- Verify there aren't any vacuum leaks
+- TUNE based on the results of the car under actual operating conditions, don't assume anything
+- THE Only way to truly know how the combo of power valve, booster type, accelerator pump cam, squirter, accelerator pump size and carb jets will work on your combo, is to try a couple different combos and see how the 60' times and the engine feels as you accelerate,
+- Reading spark plugs helps a lot
+- Changing ignition advance curves helps a lot
+- While tuning your carb you'll most likely need to change the
+	- carb jets
+	- power valve
+	- accelerator pump cam
+- These are less likely needed to be changed
+	- squirter size
+	- accelerator pump size
+	- booster type
 ----
 ## Power Valves - Vacuum Activated Fuel Enrichment Valves
-Holley carburetors utilize "Power valves" which are part of a vacuum activated fuel enrichment system
+power valves and accelerator pumps make up the Holley 4150/60's vacuum activated fuel enrichment system, AKA "power enrichment system"
-Power valves (along with accelerator pumps) provide extra fuel in addition to the fuel already flowing through the main jets in order to maintain a target AFR when *transitioning* from idle/cruise to WOT
+- The power enrichment system (which includes power valves)
+	- Supplies additional fuel to the main system during heavy load or WOT
+	- Helps maintain a target AFR *only while transitioning* from idle/cruise to heavy-load/WOT
+	- **Note:** PVs are not intended to be an enrichment circuit during normal throttle cruising when manifold vacuum is high
-A spring and diaphragm in the power valve restricts additional fuel flow until manifold vacuum drops to certain value.
+- How they work
+	- They have a spring and diaphragm that restricts additional fuel flow until the manifold vacuum *falls below* a certain value
-- Each Holley power valve is stamped with a number to indicate the vacuum opening point
+	- They're screwed into the metering plate which is located between the fuel bowl and the carb's main body
-	- For example, the number "65" indicates that the power valve will open when the manifold vacuum drops to 6.5"Hg or below (=< 6.5"Hg)
+	- Each Holley power valve is stamped with a number to indicate the vacuum opening point, for example
-	- The higher the number, the faster the power valve opens (8.5 opens sooner than a 5.5)
+		- "65" indicates that the power valve will open when the manifold vacuum drops below 6.5"Hg (=< 6.5"Hg)
+	- The higher the vacuum threshold number, the faster the power valve opens, e.g. an 85 will open sooner than a 55
-Power valves are screwed into the metering plate that's located between the fuel bowl and the carb's main body
-**Note:** Power valves are not intended to be an enrichment circuit during normal throttle cruising when manifold vacuum is high
 - "Standard Flow" PV vs a "High Flow" PV
-	- For each power valve there's a "Standard" & "High" flow rate version
+	- For each PV rated at a certain vacuum threshold, there's a "Standard" & "High" flow version which indicates orifice size
 	- Use standard flow for small blocks, up to 350 cubic inch
 	- Use high flow for big blocks, 396 and up
 #### Power Enrichment Timeline of Events
-Accelerator pumps and power valves make up the Holley 4150/60's "power enrichment system" which is designed to supply additional fuel to the main system during heavy load or full power (WOT) situations.
 - Event 0 - Idle or light cruise
-	- Manifold vacuum is high because the throttle blades are almost closed restricting flow into the intake
+	- Manifold vacuum is high because the throttle blades are almost closed, restricting flow into the intake
+	- The carb's main jets provide sufficient fuel to maintain the target AFR
 - Event 1 - The Driver presses the gas pedal
 	- This rotates the carb's throttle linkage clockwise ("open")
-- Event 2a (concurrent w/2b) - The Accelerator pump sprays an extra shot of fuel into the venturies
+- Event 2a (concurrent w/2b) - The Accelerator pump begins to spray an extra shot of fuel into the venturi
-	- The accelerator pump supplies a shot of extra fuel
+	- This produces a richer, *less detonation prone* air/fuel mixture during the transition from partly open throttle to fully open throttle
-		- The cam actuates the lever which pushes up on the diaphragm
+	- The cam actuates the lever which pushes up on the diaphragm
-		- Fuel is sprayed against the outside of the boosters for better atomization
+	- Fuel is sprayed against the outside of the boosters for better atomization
-		- This happens in just the primaries for a "Vacuum Secondary" 4150/60 and in both the primaries & secondaries for a "Double Pumper" "Mechanical Secondary" 4150/60
+	- This happens in just the primaries for a "Vacuum Secondary" 4150/60 and in both the primaries & secondaries for a "Double Pumper" "Mechanical Secondary" 4150
-	- Covers the rapid increase in air flow during the transition from partly open throttle to fully open throttle
 - Event 2b (concurrent w/2a) - The throttle blades open
 	- Manifold vacuum rapidly DEcreases
-		- Under WOT, it could drop down to 0-1.5"Hg
+		- Under WOT, it could drop all the way down to 0"Hg - 1.5"Hg
 	- The velocity of air going through the carb's venturi speeds up
 		- This rapid INcrease of air flow requires additional fuel in order to maintain a target AFR
-- Event 3a - (concurrent w/3b) - The accelerator pump has run out of stroke
+- Event 3a - (concurrent w/3b) - The accelerator pump stops spraying fuel into the venturi
+	- The accelerator pump has run out of stroke
 - Event 3b - (concurrent w/3a) - The power valve opens
-	-The diaphram on the power valve uses the now-lower manifold vacuum as atrigger to open its valve
+	- The lower manifold vacuum triggers the PV's diaphragm/spring to open its valve
-	- This allows more fuel to flow through the carb providing a richer, *less detonation prone* air/fuel mixture during WOT
+	- More fuel flows through the carb providing a richer, *less detonation prone* air/fuel mixture
-	- This prevents "bogging", "hesitations" or "coughing" when the carb's jetting alone can't keep up with demand
+	- This prevents bogging and hesitations caused when the carb's main jets alone can't keep up with the fuel demand
 - Event 4 - The Driver lets off of the gas pedal
-- Event 5a (concurrent w/5b) - The throttle blades close
+- Event 5 - The throttle blades close
+	- The velocity of air going through the carb's venturi slows down
 	- Manifold vacuum INcreases
-		- Indicative of partial-throttle, steady-speed operation like low speed cruising
+		- The throttle blades are almost closed which restricts air flow into the intake
 		- Typical values are 11-20"HG
-	- The velocity of air going through the carb's venturi slows down
+- Event 6 - The power valve closes
-- Event 5b - (concurrent w/5a) - The power valve closes
+	- The higher manifold vacuum triggers the PV's diaphragm/spring to close its valve
-	- The diaphram on the power valve uses the higher manifold vacuum as atrigger to close its valve
 	- This leans out the air/fuel mixture
-- Event 6  - The carb's internal fuel routing goes back to standard jetting
+- Event 7 - The car returns to partial-throttle, steady-speed operation, low speed cruising, or idle
-	- The carb's main jets provide sufficeient fuel for the target AFR
+	- The carb's idle circuit and/or main jets provide sufficient fuel for the target AFR
 #### Tuning power valves
-- keep in mind there's many guys chasing carb problems that are eventually traced to the ignition, or fuel system, verify the damper and timing tab really do reflect TDC and your ignition advance is working correctly, and verify you have 5 psi of steady fuel pressure at the carb and the floats are set correctly and the cars valves are adjusted and there's no vacuum leaks before you go swearing its solely a carb problem
-- If you are lean or rich during normal driving conditions, you need to tune the jets, not the power valve.
+- The initial power valve rating should be 1/2 of the manifold vacuum reading while the car is at a steady cruise or idle
-- The reason you check the vacuum at idle and take that reading and divide it in half, is so you do not have a power valve that will open at idle as this will tend too cause an excessively rich mixture at idle, or just off idle.
+	- If the vehicle has a manual transmission, take the vacuum reading with the engine thoroughly warmed up at idle in neutral
-- START the tune with the power valve used being selected too be close to 1/2 the vacume/plenum reading at a steady cruise, at minimum throttle NOT at idle in neutral
+	- If the vehicle is equipped with an automatic transmission, take the vacuum reading with the engine thoroughly warmed up, idling in gear with foot on the brake
-- TUNE based on the results youll see in actual operation, and you don,t assume anything here, your almost certainly going to need to change the power valve, jets and accelerator pump cam based on the results youll see under actual operating conditions.
+	- The reason to start with a PV rated at 1/2 of the car's idle manifold vacuum is so it doesn't open while the car's idling or just off idle. That would cause an excessively rich mixture.
-- An accurate vacuum gauge should be used when determining the correct power valve to use.
+	- **Note:** There are only "x.5" power valves, i.e. there are no "x.0" power valves. If the vacuum reading is an even number, select the next *lower* power valve.
-- A competition or race engine which has a long duration high overlap camshaft will have low manifold vacuum at idle speeds.
+** Recommended PV Sizes (to start with) **
-- Holley's instructions might be misleading (use a PV 1/2 idle vacuum)
+| Idle "Hg | PV Size
-	- They will ALWAYS lead you to choose too low a PV number, which in turn will force you to use too large jets, too much pump, etc.
+|----------|----------
-	- youll generally want to select a slightly higher number power valve if your getting a flat spot.
+| 8        | 3.5*
-	- Keep raising the PV number until that flat spot clears up.
+| 11       | 5.5 - 6.5
+| 13       | 6.5
+| 15-16    | 6.5 - 8.5
+| 16       | 6.5 - 9.5
+| 17       | 7.5 - 8.5
-you take the vacuum reading at idle and cut it in 1/2 then jump up or down one -two numbers depending on how the plugs look, the engine runs and what your fuel/air ratio meter indicates example if your pulling 16" at idle that would be a power valve in the 6.5-9.5 range
+* There's no "4.0" PV and 3.5 is next lower
-youll also see advise saying that Basing the PV selection on idle vacuum is BAD advise that has floated around for a long time. If you take CRUISE vacuum, divide it in half and add about 2" you will be close.
-read what holley says
+- Some internet ppl say
-- THE Only way to truly know how the combo of power valve, booster type, accelerator pump cam, squirter, accelerator pump size and carb jets will work on your combo, is to try a couple different combos and see how the 60' times and the engine feels as you accelerate, and both experience and knowledge of how to read spark plugs and change ignition advance curves will help a great deal.
+	- getting a manifold vacuum reading at steady cruise is better than idle
+	- Vacuum at cruise (Vc) is about equal to vacuum at idle (Vi) less 4"Hg (Vc = Vi - 4, "If you take CRUISE vacuum, divide it in half and add about 2" you will be close)
-- If the vehicle has a manual transmission, take the vacuum reading with the engine thoroughly warmed up at idle in neutral
+	- Some internet ppl say that Holley's instructions might be misleading ("use a PV 1/2 idle vacuum")
-- If the vehicle is equipped with an automatic transmission, take the vacuum reading with the engine thoroughly warmed up, idling in gear with fott on the brake
+		- They will ALWAYS lead you to choose too low a PV number, which in turn will force you to use too large jets, too much pump, etc.
+		- you'll generally want to select a slightly higher number power valve if your getting a flat spot.
-After determining the manifold vacuum in inches-mg, select a power valve thats 1/2 of that value
+		- Keep raising the PV number until that flat spot clears up.
-**Note:** There are no "n.0" power valves, there are only "n.5" power valves. If the vacuum reading is an even number, select the next *lower* power valve.
-#### Recommended Starting Sizes
-| " Hg  | PV Size
-|-------|------------
-| 8     | 3.5*
-| 11    | 5.5 - 6.5
-| 13    | 6.5
-| 15-16 | 6.5 - 8.5
-| 17    | 7.5 - 8.5
-* There's no "4.0" PV and 3.5 is next lower
 #### Broken power Valves
-- If you have a carburetor older than 1992 (or you have experi-
-enced an extreme backfire) and expect a blown power valve,
-use this simple test. TEST: At idle turn your idle mixture screws
-(found on the side of the metering block) all the way in. If your
-engine dies the power valve is not blown
-	- power valves have a diaphragm that can be ruptured
-	- a BLOWN or busted power valve will leak fuel in an irregular manor,and not regulate flow, so if it does not test correctly, you'll need to replace it, the most common cause, for a busted power valve is carb back fires
-## Accelerator Pump
-- select a 30cc or 50 cc accelerator pump volume
+power valves have a diaphragm that can be ruptured
-- the accelerator pump cam will control how fast the carbs linkager starts to cover the transition between idle and fully open venturies when the engine could go lean
-- remember that a larger squirter size does not give you more total fuel, it only allows more volume to move through the squirter faster, but this only tends to result in a shorter duration squirt, of fuel before and during the transition,as the power valves and secondary jetting add fuel and air flow
+A blown or busted power valve will leak fuel in an irregular manor and not regulate flow
+the most common cause for a busted power valve is a carb backfire
+- If you suspect a blown power valve, use this simple test:
+	- At idle turn your idle mixture screws all the way in. If your engine dies the power valve is not blown
+## Accelerator Pumps & Squirters
+select a 30cc or 50 cc accelerator pump volume
+the accelerator pump cam will control how fast the carbs linkage starts to cover the transition between idle and fully open venturi when the engine could go lean
+remember that a larger squirter size does not give you more total fuel, it only allows more volume to move through the squirter faster, but this only tends to result in a shorter duration squirt, of fuel before and during the transition as the power valves and secondary jetting add fuel and air flow
 ----

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