Carb Tuning Issues 383 w/ 670 Holley Street Avenger

Theron

Theron

Member
Continuing my issues. Vehicle: 69 Chevy C10, sm465 manual, 383 stroker, Dart Pro comp 215cc heads, edelbrock 7501 air gap intake, Holley 670 SA, comp cams XE284h-10 12-250-3, 450hp, 450 lb/ft.

Set everything to spec according to Grumpy's thread 831 on carb tuning. Set the transfer slot to .020 (looks like a square). Set the secondary throttle blades to 'even-ish' with the light test. Put it back together.

It will not idle at all. I need to come up a full turn on the primary idle screw (matched on the secondary) before it will even give me an idle that barely keeps the truck running at 500 or so rpm.

At this point, quite a bit of the transfer slot is now exposed.

No vacuum leaks detected with the propane test. Truck has nothing connected to vacuum from the carb or manifold (no power brakes, mechanical distributor controlled by a 6al2 box, manual transmission)
 
Running test at 75 primary jets and 80 secondary jets leaves a stumble/buck under 1500 rpm. Attached is a plug picture.
 

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your obviously running rather lean, why not try bumping the jet size up 2-t0-3 sizes
maybe 78-or even 80 primaries jets, verify the float levels and that you have 5-6 psi fuel presure at the carb inlet port,youll certainly se a change that will point you in the right direction
you can,t guess you need to deal in verified facts,
please post very clear pictures of your spark plugs,
whats your fuel pressure at the carb inlet port read? and check your vacuum at idle and again at 3000rpm with a vacuum gauge, then verify your ignition timing curve, check your float levels are set correctly.
a 600-750 cfm carb can be rather easily tuned on a typical chevy 350-400 it just takes experience and facts to work from, if you don,t know how to do something or what I'm talking about, ASK QUESTIONS,WE ALL START OUT with LESS THAN IDEAL EXPERIENCE
we can certainly find the cause and correct it but you need to deal in verified facts, its a simple step by step process of check, test eliminate the potential cause and re-test, Id suggest you get a timing light and b, verity TDC as a starting point then borrow, buy or find someone to help you tune that has access to one, (a fuel/air ratio scanner) and take a compression test and verify your ignition advance curve,
GENERALLY your fuel/air ratio should be in these ranges
Idle- up too about 2500 rpm try for 14.7:1-15:1 f/a ratio
from about 2500 rpm- too about 4500 rpm try to smoothly and predictably transition the fuel/air ratio mix richer to about 13.5:1
from about 4500 rpm- too about 6500 rpm and higher ,try to smoothly and predictably transition the fuel/air ratio mix richer to about 12.5:1this is only a starting point on the tune but it generally gets you in the ball park and tends to reduce the chances of the engine reaching detonation conditions.
the ignition advance curve needs to be checked, the chart below is a very good starting point to work from, and USE OF A RICHER FUEL/AIR MIX, WILL AT TIMES BE REQUIRED IN THE OFF IDLE TO 3500 rpm range
chart3e1.jpg

and yes, use of a small handy and accurate fuel pressure gauge, mounted on the fuel injector fuel rail (0-100 psi for FUEL INJECTION)
fpgg3a.jpg

or carb inlet port (0-15 psi for carburetors)is almost mandatory, they generally cost under $30
fpgg1a.jpg
fpgg2a.jpg

555-BO-1672-wGa.jpg


without testing you simply guessing

http://garage.grumpysperformance.com/index.php?threads/drop-back-to-basics.12943/#post-67323

http://garage.grumpysperformance.co...hink-logically-don-t-assume.12484/#post-62772

http://garage.grumpysperformance.co...-test-seems-to-be-a-forgotten-art-form.11838/

http://garage.grumpysperformance.com/index.php?threads/carb-tuning-info-and-links.109/

having a few basic meters,gauges etc.
IT sure helps too have basic tools, when isolating issues


MULTI METER

INFRARED TEMP GUN

TIMING LIGHT

COMPRESSION GAUGE

PRESSURE/VACUUM GAUGE
chartvac.jpg


read the links and sub links

http://garage.grumpysperformance.com/index.php?threads/verifying-your-real-advance-curve.4683/

http://garage.grumpysperformance.com/index.php?threads/carb-tuning-info-and-links.109/

http://garage.grumpysperformance.com/index.php?threads/holley-carb-power-valves.1639/

http://garage.grumpysperformance.com/index.php?threads/simple-things-u-need-to-know-setting-float-levels-etc.1115/
http://garage.grumpysperformance.co...n-670-holley-street-avenger.12305/#post-60572







https://www.youtube.com/watch?v=P7GX82ljmxg

http://www.4secondsflat.com/Carb_CFM_Calculator.html

http://www.4secondsflat.com/Carburetor Sizing and Series Charts.htm
holle3.png


http://www.amazon.com/Holley-Carburetor ... lley+carbs
holle2.png

http://www.amazon.com/Holly-Carburetor- ... AQ9Z01P4SV
https://www.youtube.com/watch?v=xSrB5ba97IY


https://www.youtube.com/watch?v=47A6_LF295o

https://www.youtube.com/watch?v=WfjkeC3dPSI
years ago I purchased two of these assortment packs when they cost about 1/2 the current price , Ive tried hard to keep 4 jets in each size in inventory as I use those, 72 jets in assorted sizes for $52 is still a good deal , and it gets better if you buy the pack or two of them, when summit posts a discount code
http://www.summitracing.com/parts/hly-36-181
hly-36-181.jpg

https://www.summitracing.com/parts/...MI3bORxpag6wIVlJgBCh3ISwMREAEYASABEgLILPD_BwE
IF you can read spark plugs , USE A TIMING LIGHT, and use an INFRARED TEMP GUN AND VACUUM GAUGE
http://www.harborfreight.com/cpi/ctaf/d ... mber=93547
A MULTI METER AND TIMING LIGHT WILL BE USEFUL
image_12926.jpg

http://www.harborfreight.com/5-in-1-dig ... 98674.html

http://www.summitracing.com/parts/MSD-8991/
timinglite6.jpg



vgauge.gif

TUNING A HOLLEY IS DAMN SIMPLE
chevfireor.gif

infrared thermometers are a very useful tool to track down issues with tuning, or mal functioning sensors
T504-4254_product.jpg

viewtopic.php?f=50&t=138&p=168&hilit=infrared#p168



IF you can read spark plugs , USE A TIMING LIGHT, and use an INFRARED TEMP GUN AND VACUUM GAUGE

TUNING A HOLLEY IS DAMN SIMPLE

http://garage.grumpysperformance.com/index.php?threads/holley-carb-power-valves.1639/

http://garage.grumpysperformance.com/index.php?threads/carb-tuning-info-and-links.109/

http://garage.grumpysperformance.com/index.php?threads/holley-accelerator-pumps-cams.1790/

http://garage.grumpysperformance.com/index.php?threads/holley-annular-vs-down-leg-boosters.5229/

http://garage.grumpysperformance.co...-the-holley-4150-and-4160-series-carbs.10736/

http://garage.grumpysperformance.com/index.php?threads/holley-carb-tune-info.264/
 
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Went to 79 primary jets. *seems* better, but I'm getting jaded at this point. Problem is still there. Here is the plug at #79. Fuel pressure is 6.5. Float levels are just at the bottom of the sight windows.
 

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#82. No change in how it runs other than it seems to bog more now.

Still surges/falls off/doesn't run right at part throttle. It idles ok. It turns off w/o dieseling at that idle point. It just won't drive on the street without kicking, bucking, surging... whatever you want to call it, it's not smooth when I am barely on the pedal.

I don't think this has to do with jetting?

Due to showing too much transfer slot at idle? It definitely is showing a lot more than .020 and I can't get it to idle any lower than where it is now.

Too small of a shooter or accelerator pump?
 

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I am driving home from working a 1/2 day Turning wrenches in my Corvette.
Its Raining.
Thinking.
 
Here's something I found on another forum:

"Problem is a street avenger isn't designed to work with a cam that big in a 350. The idle fuel circuit is set up lean for smaller cams in a 350. You might cover up the problem with pump cams and squirters, but ya really need more idle fuel. IFRs need to be bigger."

How does that sound?
 
Its Bullshit from some Ficken Moron.
I have a 770 CFM Street Avenger on my 1965 Oldsmobile 425A Ci V8 engine that I transplanted into my 1963 Pontiac Grand Prix last Month.
360 HP & 470 Ft-lbs Flywheel Power.
About a 270 advertised cam. 112 lobe centerline. 52 degrees overlap.
I can smoke the rear tires off for 500 feet stomping the gas from a dead stop.
Twin strip posi marks.
Blacktop is melted down.
15-18 mpg at 55-80 mph.
Turbo 400 trans. Stock torque converter. 3.23 gears in the 9.3" inch Pontiac rear diff.
 
Street Avenger series Holley 4150 is decent.
Metering blocks should support 500-550 Hp.
 
Lets backup and get a Story.
When did this issue come up ?
Has the bad idle and stumble allways been there ?
 
You have a Hidden Vacuum leak present or a Fuel delivery issue I suspect or both.
 
This issue has been here since the engine came off of the dyno from break in. It diesels on shutdown. It surges when driving at part throttle. The dyno reports show that the AFR is fine. The fuel bowls stay full. I have the fuel pressure regulated to 6.5. The timing is set at 31 degrees, according to the machinist, because the compression is borderline.

I have tested for vacuum leaks. I can detect none with propane.
I do not see a fuel supply issue.

At this point I give up. I've learned as much about this as I can from reading and trying to practice it. I have, LITERALLY, read every one of grumpy's posts and tangent links on the subject.

Talking to Holley tech, they say that it is stuck in a bad place between the idle circuit and the transition. It's a known flaw with carbs and this type of big cam.

What they are basically telling me is that my combination will not run on the street.
 
Let me look up this Comp Cam 284 X cam.......
It can not be that Radical.
Drag Race cams I prefer Come on Strong at 4,000 Rpms & Keep Pulling at 8,000 RPMs.
 
Dyno Results

Camshaft Part # 12-250-3 Grind # XE284H-10
Duration @ 0.006": 284° / 296° Duration @ 0.050": 240° / 246°
Max Lift w/ 1.5RR: .507" / .510" Lobe Separation: 110°
Lobe ID#'s: 5447 / 5209 Intake Centerline: 106°
Engine Type: Chevrolet 350 Small Block
Bore: 4.040" Stroke: 3.480"
Displacement: 356ci Compression: 9.25:1
Heads: Dart Sportsman II Intake: Edelbrock Victor Jr.
Carburetor: Holley 750 dbl. pmp. Exhaust: 1 3/4" Headers
Max Torque: 377 ft*lbs @ 3900 RPM Max Power: 390 HP @ 5800 RPM
Manifold Vacuum: 9.5" Hg @ 1000 RPM & 11.5" Hg @ 1200 RPM w/ no load.
 
OK. we have a published baseline & actual camshaft specs to see.
 
So why is it surging enough to shake the truck apart at part throttle? I have the mixture down at this point, it just won't run smoothly under load at less than 2000 rpm. Over that, it's fine.
 

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Lets forget about your Chassis Dyno Session.
Just gave you FLASH NUMBERS.
Not much good right now.'Piss Poor driveability is the Real Issue.
 
Let me research more.
I want to know actual IVO, IVC, EVO, EVC . Can figure out overlap.
In the Corvette world they give Bullshit numbers I cant work with.'
Tell me its the greatest big stick to match the Big Stick in thier pants.
Ain't Shit,
 
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