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-# Carbeurators+# Carburetors
 ** Just Holley 4150 & 4160 for now ** ** Just Holley 4150 & 4160 for now **
  
-THE O-RING ON THE NEEDLE AND SEAT, AND THE DIAPHRAGM IN THE ACCELERATOR PUMP, CAN BE DAMAGED BY ETHANOL IN FUEL UNLESS AN ETHANOL COMPATIBLE MATERIAL IS USED+**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
  
-## Power Valves - Vacuum activated fuel enrichment valves+- If the car is lean or rich during normal driving conditions, you need to tune the jets, not the power valve
  
-Holley carburetors utilize a vacuum operated power enrichment system+- A competition or race engine which has a long duration high overlap camshaft will have low manifold vacuum at idle speeds. 
  
-- The purpose of a power valve is  +- Before adjusting the carb's jets, or valves 
- - the accelerator pump supplies a shot of extra fuel to cover the rapid increase in air flow during the transition from partly open throttle to fully open throttle + - eliminate any possible issues with the vehicle's ignition 
- - for it to add the needed extra fuel the engine needs to transition and maintain the correct fuel/air ratio when you are under wide open throttle. + - eliminate any possible issues with the vehicle's fuel system 
- - restrict additional fuel flow until the vacuum drops to a known level stamped on the power valve rim + - Verify the damper and timing tab really do reflect TDC 
- - allows additional fuel flow, that comes in as the velocity of air through the carbs venturi speeds up and the vacuum reading drops, it opens, + - 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
  
-- It is not intended to be an enrichment circuit during normal throttle cruising.+- 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
  
-- Each Holley power valve is stamped with a number to indicate the vacuum opening point. For example, the number “65” indicates that the power valve will open when the engine vacuum drops to 6.5" or below.  +- While tuning your carb you'll most likely need to change the 
-- there's a number stamped on the power valve (EXAMPLE 6.5), that relates to the VACUUM reading the carb will need to drop below (in that case 6.5" of vacuum) before the power valve opens and adds additional fuel to what the carbs jets already allow + - carb jets  
-- the higher the number the faster the power valve opens as the vacuum drops as the throttle opens+ - power valve 
 + - accelerator pump cam 
 +- These are less likely needed to be changed 
 + - squirter size 
 + - accelerator pump size 
 + - booster type
  
-- Power valves are screwed into a metering plate between the carb fuel bowl and the carb body in many carbs+---- 
 +## Power Valves - Vacuum Activated Fuel Enrichment Valves
  
-  +power valves and accelerator pumps make up the Holley 4150/60's vacuum activated fuel enrichment system, AKA "power enrichment system"
-  +
-#### POWER ENRICHMENT SYSTEM+
  
-The power enrichment system supplies additional fuel to the +- The power enrichment system (which includes power valves) 
-main system during heavy load or full power situations. + - Supplies additional fuel to the main system during heavy load or WOT 
-Acceleration - the transition from  partly open throttle to fully open throttle+ - 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
  
-Event 0) at idle or light cruise, the car produces more vacuum because the throttle blades are almost closed restricting flow into the intake+- How they work 
 + - They have a spring and diaphragm that restricts additional fuel flow until the manifold vacuum *falls below* a certain value 
 + - They're screwed into the metering plate which is located between the fuel bowl and the carb's main body 
 + - Each Holley power valve is stamped with a number to indicate the vacuum opening point, for example 
 + - "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
  
-Event 1) The Driver presses the gas pedal, which rotates the carb's throttle linkage clockwise/open Causing both of these events to occur at the same time:+- "Standard Flow" PV vs a "High Flow" PV 
 + - 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
  
-Event 2a) The Accelerator pump sprays an extra shot of fuel into the venturies +#### Power Enrichment Timeline of Events 
- - Covers the transition from part to fully open throttle+ 
 +- Event 0 - Idle or light cruise 
 + - 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 begins to spray an extra shot of fuel into the venturi 
 + - 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
- - Only primaries for a "Vacuum Secondary" 4150/60; both 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 
- +- Event 2b (concurrent w/2a) - The throttle blades open 
-Event 2b) The throttle blades open causing a + - Manifold vacuum rapidly DEcreases 
- - Rapid INcrease in air flow  + - Under WOT, it could drop all the way down to 0"Hg - 1.5"Hg  
- - Rapid DEcrease in vacuum level + - The velocity of air going through the carb's venturi speeds up 
- - as you open the carb throttle blades vacuum drops off and flow increases, at some point the carbs increased air flow requires additional fuel to maintain the correct fuel/air ratio + - This rapid INcrease of air flow requires additional fuel in order to maintain a target AFR 
-  +- Event 3a - (concurrent w/3b) - The accelerator pump stops spraying fuel into the venturi 
-Event 3a) + - The accelerator pump has run out of stroke 
- - the accelerator pump has mostly run out of stroke +- Event 3b - (concurrent w/3a) - The power valve opens 
- + - The lower manifold vacuum triggers the PV's diaphragm/spring to open its valve 
-Event 3b) + - More fuel flows through the carb providing a richer, *less detonation prone* air/fuel mixture 
-- the power valve opens to flow extra fuel during the transition period and while the accelerator pump is also adding fuel, . Under WOT the vacuum of the engine will drop to a vacuum reading of 1.5 or even lower near zero and the power valve will then open adding the extra fuel needed during WOT. + - This prevents bogging and hesitations caused when the carb's main jets alone can't keep up with the fuel demand 
-- the power valve allows additional fuel to flow, as the plenum vacuum drops. +- Event 4 - The Driver lets off of the gas pedal 
-- the diaphram on the power valve senses the throttle is open and opens a valve which allows a richer fuel/air ratio mixture to flow until you lift off the throttle . +- Event 5 - The throttle blades close 
-- The power valve senses low vacuum and opens up and allows more fuel to flow through the carberator allowing a richer and better, less detonation prone power producing mixture, and thus you don,t get a big "BOG" or cough when the carb suddenly ingested more air and the carbs jetting alone can,t keep up with demand,  + - The velocity of air going through the carb's venturi slows down 
-- the power valve controls the point where that fuel starts to be added using the drop in intake vacuum as the trigger to release more fuel. + - Manifold vacuum INcreases 
-  + - The throttle blades are almost closed which restricts air flow into the intake 
-Event 4) + - Typical values are 11-20"HG  
- - as the vacume reading increases the power valve senses the increase and then it closes +- Event 6 - The power valve closes 
- - Leaning its mixture out for only partial throttle open operation used for steady speed operation like durring low speed cruising. + - The higher manifold vacuum triggers the PV's diaphragm/spring to close its valve 
- - the power valve fuel supply flows fuel until you lift off and the vacuum in the intake plenum increases, and shuts it off. + - This leans out the air/fuel mixture  
- - keep in mind the power valve supplys extra fuel as the vacuum drops as the throttle blades open in the transition process from idle to full throttle,  +- Event 7 - The car returns to partial-throttle, steady-speed operation, low speed cruising, or idle 
- + - The carb's idle circuit and/or main jets provide sufficient fuel for the target AFR
-Event 5) +
- - and the carbs fuel delivery internal fuel routeing goes back to standard jetting+
  
 #### Tuning power valves #### 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 #### 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
  
-"Standard Flow" PV vs a "High Flow" PV +select a 30cc or 50 cc accelerator pump volume
-- There's a standard & high flow rate version for each power valve +
-- match the fuel flow rate of the power valve to the engines needs +
- - standard flows work well for the small blocks (up to 350 cubic inch) +
- - high flows work better on big blocks (396 and up)+
  
 +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
  
 +----
 ## Holly "List Numbers" ## Holly "List Numbers"
  
playground/playground.1677079236.txt.gz · Last modified: 2023/02/22 15:20 by 1b3r1c0

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