Holly Carburetor.
Melting Slicks
Joined: May 2002
Posts: 2,717
Likes: 121
From: Sulphur LA
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
Jim and resdoggie are leading you in the right direction,
I don't want to distract from their help so I haven't posted but thought this would help with what they have posted,
https://forums.holley.com/entry.php?...uretor-Stumble
Neal
I don't want to distract from their help so I haven't posted but thought this would help with what they have posted,
https://forums.holley.com/entry.php?...uretor-Stumble
Neal
Thread Starter
Burning Brakes
Joined: Apr 2013
Posts: 1,072
Likes: 61
From: Saint clair shores Michigan
Barrels 4
Billet Color None
Booster Straight
Brand Holley
CFM 750
Choke Electric
Circuit 2
Emission Code 1
Finish Shiny
Fuel Gasoline
Fuel Inlet Dual
Material Aluminum
Model 4160
Primary Main Jet 72
Primary Power Valve 6.5
Primary Pump Nozzle Size 31
Product Type Carburetor
Secondaries Vacuum
Supercharged Application No
Throttle Bore 1.688 inch
Part Number 0-80508SA
Neal
Billet Color None
Booster Straight
Brand Holley
CFM 750
Choke Electric
Circuit 2
Emission Code 1
Finish Shiny
Fuel Gasoline
Fuel Inlet Dual
Material Aluminum
Model 4160
Primary Main Jet 72
Primary Power Valve 6.5
Primary Pump Nozzle Size 31
Product Type Carburetor
Secondaries Vacuum
Supercharged Application No
Throttle Bore 1.688 inch
Part Number 0-80508SA
Neal
Racer
Joined: Jan 2013
Posts: 302
Likes: 2
From: Sayville New york
yes neal that is my carb. today after reading forum i warm her up , shut down checked both fuel level ports. then removed # 31 squirter and replaced with # 37, WOW about 80% of the stumble is gone. A/F gauge went from 20.2 to 13.45 when you open throttle with car in park from idle to 2000rpm being very careful not to engage secondary.what will my next move be ?i should i have mention i have the blue plastic cam on top screw for accelerator pump.thank you Resdoggie/427 hotrod
Last edited by Captain bob; Dec 11, 2017 at 06:30 PM.
Had a 1976 L-82, 4-sp
Joined: Mar 2011
Posts: 5,338
Likes: 1,213
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Jim and resdoggie are leading you in the right direction,
I don't want to distract from their help so I haven't posted but thought this would help with what they have posted,
https://forums.holley.com/entry.php?...uretor-Stumble
Neal
I don't want to distract from their help so I haven't posted but thought this would help with what they have posted,
https://forums.holley.com/entry.php?...uretor-Stumble
Neal
Had a 1976 L-82, 4-sp
Joined: Mar 2011
Posts: 5,338
Likes: 1,213
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
yes neal that is my carb. today after reading forum i warm her up , shut down checked both fuel level ports. then removed # 31 squirter and replaced with # 37, WOW about 80% of the stumble is gone. A/F gauge went from 20.2 to 13.45 when you open throttle with car in park from idle to 2000rpm being very careful not to engage secondary.what will my next move be ?i should i have mention i have the blue plastic cam on top screw for accelerator pump.thank you Resdoggie/427 hotrod
Racer
Joined: Jan 2013
Posts: 302
Likes: 2
From: Sayville New york
will give timing curve ASAP with and without HEI vacuum advance (this is a fully adjustable type as a add-on now set at 12 degrees max) mechanical is 36 degrees at 3000, weights and stops are OEM springs using one heavy and one medium.total vacuum and mechanical at 3600 is 54 degrees but will give increments. given a choice would you up squirter to 40 with hollow screw or change to 50mm pump diaphragm first. the video suggests any squirter 37 and above should use this.mat take a while for my speed shop to purchase this.
Last edited by Captain bob; Dec 11, 2017 at 09:33 PM.
Race Director
Joined: Jan 2000
Posts: 13,018
Likes: 2,262
From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
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Congratulations! Sounds like you're going the right way. Nail down your timing and then tweak some more.
Until you change the squirter...the larger pump isn't needed. It won't make a difference otherwise by itself.
I think you'll end up with cam in #2 position (will need to readjust pump) before it's all over with.
Then you can work on vacuum sec opening rate.
JIM
Until you change the squirter...the larger pump isn't needed. It won't make a difference otherwise by itself.
I think you'll end up with cam in #2 position (will need to readjust pump) before it's all over with.
Then you can work on vacuum sec opening rate.
JIM
Had a 1976 L-82, 4-sp
Joined: Mar 2011
Posts: 5,338
Likes: 1,213
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
A 0.040" squirter worked for me and I didn't need to change the accl pump size as Jim noted. My 650 street hp came with two pink cams in hole #1 and I didn't need to change them either to eliminate the hesitation. However, you may need to do so but educate yourself on what cams do and how it effects the squirters. It's a lot of trial and error to get it right but following Holley's tuning method and listening to the guys in here helped immensely.
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Verdad Gallardo
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
will give timing curve ASAP with and without HEI vacuum advance (this is a fully adjustable type as a add-on now set at 12 degrees max) mechanical is 36 degrees at 3000, weights and stops are OEM springs using one heavy and one medium.total vacuum and mechanical at 3600 is 54 degrees but will give increments. given a choice would you up squirter to 40 with hollow screw or change to 50mm pump diaphragm first. the video suggests any squirter 37 and above should use this.mat take a while for my speed shop to purchase this.
Most people think that a 30cc pump diaphragm actually shoots 30cc when you hit the full throttle. Not true. The diaphragm plunger only discharges a portion of the 30cc. There is still a reserve left in there. H-m-m-m. If you are not using 30. Sure don't need 50.
Last edited by HeadsU.P.; Dec 12, 2017 at 09:59 AM.
Racer
Joined: Jan 2013
Posts: 302
Likes: 2
From: Sayville New york
so does line boring the cam shaft journals to coincide with lined bored mains but we do every day on CNC machine but never touch a carburetor
Last edited by Captain bob; Dec 12, 2017 at 10:15 PM.
Racer
Joined: Jan 2013
Posts: 302
Likes: 2
From: Sayville New york
today remove # 37 squirter and replaced with @ 40 --------no stumble!!!!!! however timing not good (vacuum advance plugged) reads 17 @ 800 ,29 @1500 , 32 @2000 ,34 @ 2500 , 36 @ 2800 , 40 @3500 ,42 @ 3800 does not change after 3800 rpm. Resdoggie what made you think timing? now i have to try trial and error on the stops in dizzy, -------thank you
Racer
Joined: Nov 2017
Posts: 289
Likes: 32
It never ceases to amaze me how most car enthusiasts install carburetors that are grossly oversized for their street engines just because the "racer guy" down the street recommended one that big. The result is a very poor performing engine at low engine speeds because of lousy air/fuel mixing and often use intake manifolds that are intended for continuous 5000+ rpm operation.
Burning Brakes
Joined: Jul 2014
Posts: 831
Likes: 54
From: Arlington TX
today remove # 37 squirter and replaced with @ 40 --------no stumble!!!!!! however timing not good (vacuum advance plugged) reads 17 @ 800 ,29 @1500 , 32 @2000 ,34 @ 2500 , 36 @ 2800 , 40 @3500 ,42 @ 3800 does not change after 3800 rpm. Resdoggie what made you think timing? now i have to try trial and error on the stops in dizzy, -------thank you
Race Director
Joined: Jan 2000
Posts: 13,018
Likes: 2,262
From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
C2 of Year Winner (performance mods) 2019
2017 C2 of Year Finalist
today remove # 37 squirter and replaced with @ 40 --------no stumble!!!!!! however timing not good (vacuum advance plugged) reads 17 @ 800 ,29 @1500 , 32 @2000 ,34 @ 2500 , 36 @ 2800 , 40 @3500 ,42 @ 3800 does not change after 3800 rpm. Resdoggie what made you think timing? now i have to try trial and error on the stops in dizzy, -------thank you
Going good. I'd use more initial advance and limit total. 20+ initial would be good with a limit in total to 34-36* maybe.
The actual changes you're making are very simple ones...which is why Holley's are popular. We just needed to get you pointed the right direction. You got this!!
JIM
Last edited by 427Hotrod; Dec 12, 2017 at 10:43 PM.
Tech Contributor
Joined: Jun 2004
Posts: 20,910
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
It never ceases to amaze me how most car enthusiasts install carburetors that are grossly oversized for their street engines just because the "racer guy" down the street recommended one that big. The result is a very poor performing engine at low engine speeds because of lousy air/fuel mixing and often use intake manifolds that are intended for continuous 5000+ rpm operation.
Some of us think that engine choices are an analog (bell curve) choice. There are a few engines that are strictly designed to get the utmost in fuel economy (and horsepower be damned) while other engines are designed for the utmost in horsepower (and mileage/durability be damned). Most of us drive/race cars with engines somewhere in the middle (a decent compromise of horsepower/economy/durability).
There's no single (or dual) answer for everybody.
Race Director
Joined: Jan 2000
Posts: 13,018
Likes: 2,262
From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
C2 of Year Winner (performance mods) 2019
2017 C2 of Year Finalist
Also interestingly...these simple tuning tips will make the OP love his 650 on his 383 with a 3500 converter....and Bob's nasty 408" is going to rock when it's all done.
We're working with "universal" carbs on completely redesigned engines...cams, heads, intakes etc. Tweaking a carb is just part of the deal and a Holley makes it easy.
JIM
We're working with "universal" carbs on completely redesigned engines...cams, heads, intakes etc. Tweaking a carb is just part of the deal and a Holley makes it easy.
JIM
Race Director
Joined: Dec 1999
Posts: 11,096
Likes: 990
From: Sierra Foothills CA
It never ceases to amaze me how some people think that engines are a binary choice: either street or race.
Some of us think that engine choices are an analog (bell curve) choice. There are a few engines that are strictly designed to get the utmost in fuel economy (and horsepower be damned) while other engines are designed for the utmost in horsepower (and mileage/durability be damned). Most of us drive/race cars with engines somewhere in the middle (a decent compromise of horsepower/economy/durability).
There's no single (or dual) answer for everybody.
Some of us think that engine choices are an analog (bell curve) choice. There are a few engines that are strictly designed to get the utmost in fuel economy (and horsepower be damned) while other engines are designed for the utmost in horsepower (and mileage/durability be damned). Most of us drive/race cars with engines somewhere in the middle (a decent compromise of horsepower/economy/durability).
There's no single (or dual) answer for everybody.
Racer
Joined: Nov 2017
Posts: 289
Likes: 32
Here's some numbers showing just how much air a 350" street engine can consume at various rpm's and at a very reasonable 90% volumetric efficiency (free flowing intake and exhaust).
1. 635 cfm @ 7000 rpm
2. 547 cfm @ 6000 rpm
3. 456 cfm @ 5000 rpm
4. 365 cfm @ 4000 rpm
5. 274 cfm @ 3000 rpm
6. 182 cfm @ 2000 rpm
When a mechanical secondary carburetor is ran wide open at low engine speeds the venturi velocity drops so low the engine loses power because of poor air/fuel mixing. But an AVS or vacuum secondary carburetor won't begin to open its secondaries until the engine is able to use the additional air and that air is introduced gradually to prevent bogging. Almost all of the 60's G.M. muscle cars used the Rochester QuadraJets because of their ability to be used on virtually any size of engine from 250" to 500" and everything in between. The Rochester QuadraJet is one of the very best carburetors ever made for street engines.
1. 635 cfm @ 7000 rpm
2. 547 cfm @ 6000 rpm
3. 456 cfm @ 5000 rpm
4. 365 cfm @ 4000 rpm
5. 274 cfm @ 3000 rpm
6. 182 cfm @ 2000 rpm
When a mechanical secondary carburetor is ran wide open at low engine speeds the venturi velocity drops so low the engine loses power because of poor air/fuel mixing. But an AVS or vacuum secondary carburetor won't begin to open its secondaries until the engine is able to use the additional air and that air is introduced gradually to prevent bogging. Almost all of the 60's G.M. muscle cars used the Rochester QuadraJets because of their ability to be used on virtually any size of engine from 250" to 500" and everything in between. The Rochester QuadraJet is one of the very best carburetors ever made for street engines.