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Holley Carb ?'s

26K views 21 replies 5 participants last post by  TeamRush 
#1 ·
I saw a post on the forums from year 2000 from a guest that had almost the same setup as I did (258 w/ Crane 260 cam, Clifford intake and exhaust, and Holley 2300 7448 carb). Just wondering if that person is around or if anybody has a similar setup and could let me know what tuning they had done to the carb?

Mine came with 8.5 powervalve and 61 jets. Just wondering if that has worked for folks on the 258.

Thanks.
 
#3 ·
How about I tell you how to tune your Holley so it works with YOUR engine?

First off, you need a VACUUM GAUGE.

You need a vacuum gauge to set the idle mixture,
And to determine the correct power valve to use.

There are a number of steps to tuning a Holley correctly, and you should do them all so your Holley does what it's supposed to do!

Start with checking the base plate for vacuum leaks!
Any vacuum leak will cause problems with everything from idle mixture to power brakes!

--------------------------------------------------

Secondly, Throttle linkage adjustment.
Make sure you have some slack in the throttle linkage so when you put the jeep in a bind, it doesn't pull the throttle linkage open.

Check to make sure when someone PUSHES THE THROTTLE PEDAL TO THE FLOOR, THE THROTTLE BLADES IN THE CARB ARE PERPENDICULAR!
Don't just stand beside carb and open linkage,
Actually have someone push the pedal down!

----------------------------------------

Third, Check your accelerator pump linkage, make sure it starts to move the INSTANT the throttle blades start to move!
If there is any 'Gap', you will get a 'Bog' or 'Stumble' when you try and move from a stop.



---------------------------------------------

Fourth, Take the SIGHT PLUG screw out of the float bowl(s)...
So when you start the engine, you can adjust your fuel float level.





Remember!
The SCREW in the adjuster is the LOCK SCREW,
And the 'NUT' is the adjuster!

Most 'Off Road' guys wan the fuel level to be just barely getting into the threads of the sight plug hole,
Serious off roaders will want fuel level about 1/16" to 1/8" below the threads.

THERE WILL BE FUEL SPILLAGE!
Engine (or fuel pump if you have electric) MUST be running before you can adjust the fuel level,
And you should NEVER adjust fuel level INDOORS!
Always have a fire extingusher handy!


--------------------------------------------------

Fifth, Screw in the idle mixture screws LIGHTLY, then back out about 1.5 turns.

Hook up the vacuum gauge to base plate vacuum, and turn the idle mixture screws TOGETHER (ALWAYS TOGETHER!) 'IN' until you get the highest STEADY vacuum.

If you go too far in, the idle will move around, and the vacuum will NOT be steady.
If you go even farther in, the engine will die.

You are looking for the highest STEADY vacuum, and you are looking to have the screws EVEN, both the same amount 'Out'.

------------------------------------------------------

Sixth,
Use that vacuum gauge with LONG HOSE, and place it so you can see the gauge while driving.
Find a flat, long stright stretch where you can drive and keep an eye on the vacuum gauge...

Get up to 55 MPH, keep the throttle STEADY and just CRUISE down the highway.
This is called 'Part Throttle Cruise', and you want to take the vacuum reading at 'Part Throttle Cruise'.

That vacuum reading at PTC will determine the correct size Power Valve...
Most people want the Power Valve 1.5 to 2.0 In.Hg. LOWER than the PTC vacuum reading.
IE: If your vacuum at PTC is 8.5 In.Hg., most people would want a 6.5 In.Hg. power valve.

Street rodders will want to get CLOSER to the vacuum reading, so the power valve opens sooner and gives extra fuel.

Average commuters will want the power valve to open about 2.0 In.Hg. below the PTC vacuum reading, so it saves fuel, but still does it's job.

Serious off roaders will often go 2.5 to 3.0 In.Hg. below the PTC vacuum reading, so the Power Valve doesn't open on the trail when they are trying to 'Finesse' an obstacle at low RPM/Speed...

--------------------------------------------------

Seventh,
Make sure your distributor is hooked up to SPARK PORTED VACUUM!
If you don't, your distributor vacuum advance will not function correctly...
 
#4 ·
Nice write up TR!!!!!!!!!!!!!!!!!!!!!!!!

IMHO - Holly's are probably the best carbs ever made - IF you understand them. Plus they have so many "goodies" available to make them even better depending on the application.

The only thing I don't like about them is they have so many teeny tiny passages that a piece of grit that you "wouldn't even feel in your eye" will plug them.

Off road they seem to need constant attention. Even with the best filtration system, somehow that little hunk of grit finds it's way in.

For street or racing applications they are tops!
 
#5 ·
TR thanks for the in depth info. Once I can get it to start I'll do exactly that.

Currently it won't run at a normal idle. If I set the curb idle very high it will stumble and 'run' with black exhaust (still haven't gotten exhaust done past the header). I've tried adjusting the idle mixture screws with no discernable effect.

It seems to be dumping too much fuel into the intake at idle, even with the idle mixture screws set 1/4 turn open.

I rebuilt the carb (new gaskets, power valve, accelerator pump) while the engine was in pieces. Broke off one of the mounting fingers on the base plate when mounting and then found a 7448 carb on ebay and used the base plate from that carb with the upper from my original.

More description to follow.
 
#8 ·
TR thanks for the in depth info. Once I can get it to start I'll do exactly that.

Currently it won't run at a normal idle. If I set the curb idle very high it will stumble and 'run' with black exhaust (still haven't gotten exhaust done past the header). I've tried adjusting the idle mixture screws with no discernable effect.

It seems to be dumping too much fuel into the intake at idle, even with the idle mixture screws set 1/4 turn open.

I rebuilt the carb (new gaskets, power valve, accelerator pump) while the engine was in pieces. Broke off one of the mounting fingers on the base plate when mounting and then found a 7448 carb on ebay and used the base plate from that carb with the upper from my original.

More description to follow.
You really CAN NOT play 'Mix & Match' with the throttle bodies...
There are different vacuum routings, and some carbs were 'Emissions' models, and their throttle bodies are completely different than the rest of the Holley line.
-------------------------------

Two things you might consider,
If you CAN NOT get the engine to IDLE,
And the idle mixture screws are set at 1.5 turns out,
Then you have fuel FLOODING the engine.
ADJUST YOUR FLOAT LEVEL!

Chances are your float level is WAY OFF!
This is what it SHOULD look like if you remove the 'Lock Screw' in the top,



Many times, you will find the needle and seat inlet valve screwed WAY DOWN below the ADJUSTER NUT...



BE VERY CAREFUL getting the Needle & Seat Inlet Valve back out!
It's made of brass, so it's fairly sturdy,
But the BOWL IS NOT! IT's made of a high quality Zinc, and the threads will distort and be damaged VERY EASILY!
SO BE CAREFUL while you are recovering the Inlet Valve!



Turning the 'Nut' RIGHT LOWERS the fuel level.
Turning the 'Nut' LEFT RAISES the fuel level.
---------------------------------

If your curb idle setting is open far enough that it's uncovering the TRANSFER SLOTS, then you are NEVER going to have 'IDLE' since you are getting into the Main Jets once you uncover the transfer slots...

Make sure the BACK BLADES are closed,



------------------------------

Then adjust your front Curb Idle so the blades in the throttle body are covered...





------------------------------------------

A third option for WAY TOO MUCH FUEL if the float level is properly set,
And the transfer slots aren't uncovered is POWER VALVE PROBLEMS...

One of the BIGGEST problems I run into is blown power valves (no backfire valve in the throttle body) and the WRONG GASKETS under the power valve.





-------------------------------------

Something that DOES happen, but is fairly rare...

Siphon from the accelerator pump circuit...
If some of the check valves stick open, and there isn't a 'Anti-Siphon' valve in the Venturi body,
You can get fuel siphoning from the Accelerator Pump Nozzles ('Shooters') and running right directly down the Venturi bore.
 
#6 ·
To conclude my thoughts:

Short of a significant fitting issue with the upper to the base plate, I don't know how else fuel could be getting past the mixture screws. I believe on the 2 bbl there are 'transfer passages' below the throttle plate when it is closed that allow the fuel that comes past the idle mixture screws to get into the intake with closed throttle.

Brand new 6.5 power valve this morning made no apparent difference.

Elsewhere someone had said the black exhaust was due to weak ignition. Now I have a new distributor/coil/rotor, all spark plug wires have reasonable resistance readings and brand new plugs.

Any thoughts would be appreciated.
 
#10 ·
Sounds like the throttle bodies are the same type then, you may just get away with this 'Mix & Match' after all!

You should only have ONE metering plate, and one metering block.
(Block Front, for power valve and jets, ect.

There shouldn't be one in the back, it should be just a metering plate screwed onto the venturi body,
But I can't tell for sure until you give me the LIST NUMBER off the choke horn so I can look up the stock parts it's 'Supposed' to have.
 
#11 ·
Carb is a 7448-1 (at least that is what is above the date code on the air horn). I believe it came 'stock' with 8.5 power valve and 61 jets.

Ended up taking the carb apart and cleaning it with nearly a whole can of carb cleaner. All the passages in metering plate and airhorn.

Now the engine seems almost ready to catch and run, but I ran out of time. Stuck out in Idaho for the next week an a half, while the jeep is in NC. Hope it is just a timing issue now and can get started when I get back.

Can you think of a reason why it wouldn't start at idle, and would only start at part throttle, but limp along with lots of black smoke?

Thanks again for all the help.
 
#12 ·
Carb is a 7448-1 (at least that is what is above the date code on the air horn).
I believe it came 'stock' with 8.5 power valve and 61 jets.
List 7448-1 (now we are getting somewhere!)
What it is, and what it came with from Holley...

Model 2300,
350 CFM,
Renew Kit 37-1536,

Trick Kit 37-933,

Needle & Seat 6-504 (off road p/n 6-513 recommended)
Holley 6-513 - Holley Needle and Seat Assemblies

Primary Main Jet 122-61 (That's a 61 jet for the layman)

Primary Metering Block 134-203

Power Valve 125-85 (that's an 8.5 In.Hg. Closing Point Power valve)
You should get a part throttle cruise vacuum reading and put in the proper power valve...

Accelerator Pump Discharge Nozzle 0.031"

Primary Bowl Gasket 108-83-2

Primary Metering Block Gasket 108-89-2

Primary Fuel Bowl 134-103
(Center Pivot, not the best for off road applications)

Throttle Body & Shaft Assembly 12R11070A

Venturi Diameter 1-3/16"

Throttle Bore Diameter 1-1/2"

This should be a 350 CFM, 2 barrel with CENTER PIVOT float bowls... and it's a 'Universal Application' unit.

Up until now, I wasn't sure if it was 2 or 4 barrel, vacuum secondary or mechanical secondaries if it was a 4 barrel.
All Holley correspondence should start with the 'LIST' number first and foremost!
-------------------------------------------------------

Ended up taking the carb apart and cleaning it with nearly a whole can of carb cleaner. All the passages in metering plate and airhorn.
You really should use carb cleaner 'DIP' for cleaning the carb.
The stuff in the spray cans is mostly just to take the dust off the outside.

Can you think of a reason why it wouldn't start at idle, and would only start at part throttle, but limp along with lots of black smoke?
Covered this before...
My first though is way too much fuel pressure.
This carb should see a MAXIMUM of about 6 PSIG,
And it will probably run better with about 3 PSIG.

The second thing I would check is the throttle cable to make sure it's not holding the blades open.

The third thing I would check is the CURB IDLE screw to make sure it's not holding idle open to the point of uncovering the transfer slots (Which will make it run WAY too rich at idle)...

The fourth thing I'd check is to make sure the throttle blades aren't closing completely.
Bent or mis-adjusted linkage will cause the blades to seal in the bores, cutting off air, and the vehicle won't idle.

My FIFTH thought is to adjust the fuel inlet float as directed earlier.

Sixth, adjust the idle mixture as directed earlier...

Then I'd adjust the POWER VALVE as described earlier...

If I had the carb off (like for adjusting the blade opening at idle) I would check for, and install if necessary, a 'Back Fire' valve in the throttle plate.

It's VERY easy to tune a Holley if you follow the directions and pay attention to the details...
 
#13 ·
TR - you say the center pivot bowls are NOT the best for off road?
Why?

Seems like the side pivot types on a sidehill leaning one way it'd go too rich, the other way too lean.

For up and downhill, I've always installed the jet and vent extenders (inside the bowls) for off road use. What am I missing?

Good info on his!
 
#17 ·
TR - you say the center pivot bowls are NOT the best for off road?
Why?
Because center pivot bowls have big wide flat bottom floats that like to end load when you are in off camber situations.
(Float is Up-Side-Down in this picture)



Side pivot float bowls have rounded floats that don't side load, and do a MUCH better job in off camber situations.
Float is up-side-down in this picture...


------------------------------------------------

Seems like the side pivot types on a sidehill leaning one way it'd go too rich, the other way too lean.
You would be assuming the float in a side pivot was mounted off center so the varying fuel level on one side or the other effected it directly...

That ASSUMPTION would be incorrect.
Side pivot still has the ROUNDED float bottom centered in the bowl, so the fuel inlet metering is pretty well regulated until you uncover one of the Main Jets or Idle Fuel Pickup Tubes...


(Image Courtesy Of HOLLY CARBS! Thanks Holley!)

This image of a side pivot float bowl is a little biased,
Remember, if you look dead on at the end, instead of this angled shot,
The float will be MUCH more to the center of the bowl, and the rounded bottom will work MUCH better at off camber angles!
----------------------------------------

For up and downhill, I've always installed the jet and vent extenders (inside the bowls) for off road use. What am I missing?
Not much with the vent 'Whistles', I recommend them myself...
Holley 26-89 - Holley Fuel Bowl Vent Baffle


And a Vent Screen will help slow down any fuel escaping from the float bowls, without getting in the way of venting the bowl...
Holley 26-39 - Holley Fuel Bowl Vent Screens


As far as jet extension go,
Remember, if you have a CENTER PIVOT float bowl, and you want to use Jet Extensions,
YOU MUST USE A FLOAT WITH THE CORRECT 'NOTCHES' IN IT TO CLEAR THE JET/EXTENSIONS!
Holley 116-10 - Holley Carburetor Float Kits


Here are the 'Short' Jet extensions, which I like the best for off road use,
Holley 122-5000 - Holley Main Jet Extensions


YOU DO NOT NEED A SPECIAL FLOAT IF YOU HAVE A SIDE PIVOT FLOAT BOWL!
The Jet Extensions/Jets will clear the float without special floats in side pivot bowls.
----------------------------

Back to the vents...

If you look up some of my posts from 10 years ago concerning Holleys, you will find I show several ways to raise the vent tubes up off the Venturi bodes...

We have used everything from copper tubing to raise the float vents up (so fuel doesn't leak out on steep 'UP/DOWN' hill climbs/desents,
To rubber tubing slipped over the slash cut vent tubes...

Now Holley is producing the 'Truck Avenger' carb for 'Off Road' use, and it comes with a raised vent tubes over choke horn...

Look at the tube crossing the Venturi Opening with the holes drilled in it....
This is the same thing we did with copper tubing and brake line for years, good to see Holley started doing it!



Also notice the side pivot float bowls on this 'Off Road' carb,
Along with a removable top for the vacuum secondary spring change!
Man, it was a REAL pain in the butt to change vacuum secondary springs before this little gadget came along!

Holley 20-59 - Holley Vacuum Secondary Carburetor Accessories


Once you get the vent point moved to the center of the bowl (instead of the back wall) you don't get NEARLY as much flooding from the front bowl when going UP hill,

Get the opening of the vents up off the Venturi body and the fuel can't spill into the Venturis like it did before

Get the Jets to the center of the bowl, you don't get the Jets being UNCOVERED when you go DOWN a hill,

And get the Leverage Force point to the center of the bowl with a round float you don't have nearly the Side Loaded fuel problems anymore...

Reduce the opening point for the power valve, and you don't get flooding when you are trying to 'Finesse' an obstacle and the vacuum drops under load,

Get a spring loaded needle and set in there so washboards or hard drops off things don't let too much fuel in...

And the Holley becomes a seriously FORMIDABLE off road carb!
 
#14 ·
TR -

Thanks for the info. I have been using the gaskets and parts from the Trick kit in the rebuild. Only change is that the trick kit came with 5.5, 6.5, 7.5 power valves. If I could get it started I would be able to do about the second half of what you said.

One other thought I had is that timing is still off. If I am seeing about 10 degrees BTDC just cranking with the starter that is probably too much advance (at least I think). No vacuum advance hooked up, so the mechanical advance is probably not really kicking in, but once it idles the RPM will climb and I'll get some more advance maybe putting me in the 16-20 range?

Thanks for all the info again.

Mark
 
#18 ·
TR -

Thanks for the info. I have been using the gaskets and parts from the Trick kit in the rebuild. Only change is that the trick kit came with 5.5, 6.5, 7.5 power valves. If I could get it started I would be able to do about the second half of what you said.
If I were you,
I'd start with a big, honkin' fuel filter!
No such thing as 'Too Clean' of fuel!

I use the large 'See Through' plastic fuel filters.
Since I change them OFTEN, they don't get a chance to get cloudy or get old and crack.

'See Through', or 'See Into' fuel filters will allow you to observe if fuel is getting into/through your system correctly,
And you can look for things like bubbles that would indicate leaks in the lines or holes in the fuel pump diaphragm.

A fuel pressure gauge AFTER the FILTER, as in between filter and carb,
Is ALWAYS a good idea!
See Through filter lets you know you ARE getting fuel,
The gauge lets you know if the fuel is getting THROUGH the filter and if the pressure is correct from the pump...
-----------------------------

The second thing I would do is make sure your throttle blades aren't opening to the point of uncovering the transfer slots when the engine is running.

I posted pictures of the transfer slots, and where they will be located in the throttle body bores...

If you uncover the transfer slots too soon, you will get WAY too much fuel...
---------------------------------

Another through that crosses my mind,
Which gasket did you use for the Metering Block to Venturi Body?

The wrong metering block gasket,
Or not remembering to put on fresh 'O' rings on the transfer tube (if you have one) will cause MAJOR fuel metering problems!
----------------------------------

One other thought I had is that timing is still off. If I am seeing about 10 degrees BTDC just cranking with the starter that is probably too much advance (at least I think). No vacuum advance hooked up, so the mechanical advance is probably not really kicking in, but once it idles the RPM will climb and I'll get some more advance maybe putting me in the 16-20 range?
I would start from SCRATCH, and VERIFY the ignition timing before I went any farther...

It's VERY easy to do, takes basic tools, and will make things MUCH easer to diagnose!

Simply take the #1 spark plug out,
Turn the engine over BY HAND with a wrench/socket on the center bolt of the crankshaft...

Find when COMPRESSION stroke starts by putting your finger over the #1 spark plug hole, and turning the engine BY HAND!

If you use the starter, more than likey the momentum of the crank will carry your engine PAST compression stroke of #1 since there is no COMPRESSION BACKPRESSURE to slow the crank down...
SO DO NOT USE THE STARTER TO TURN THE ENGINE OVER!

Once you have VERIFIED COMPRESSION STROKE STARTING on #1 Cylinder,

Then stick a chop stick, wooden dowel rod, ect. in the spark plug hole.
DO NOT USE METAL!
You would be Amazed how fast a metal object can screw up cylinder walls, piston top, spark plug threads, ect.

Use the wooden dowel rod to locate the top of the piston,
You crank the engine BY HAND to look for the highest point of the piston on COMPRESSION STROKE!

This is VERIFYING TDC OF COMPRESSION STROKE.

Now that you have MANUALLY VERIFIED TDC OF COMPRESSION, and there is NO QUESTION you have TDC of Compression stroke,

Take a look at the balancer 'Hash' mark, and see if it lines up (roughly) with the 0° (zero) mark on your timing tab on the front cover.

*IF*...
The balancer 'Hash' mark lines up with the 0° mark (within two or three degrees) you have a balancer that hasn't had the outer ring slip on the hub yet.

Balancer outer rings are suspended in rubber between hub and ring... The rubber degrades and the outer ring slips, and causes no end of problems with timing!
You are reading 8° of advance, but if the balancer ring slipped, you might have 18 degrees of initial advance!

VERIFY THE RING 'HASH' MARK AT ROUGHLY 0° WITH THE CRANK AT TDC OF COMPRESSION.

Then locate the #1 plug wire on the distributor cap,
Follow that plug to it's terminal on the distributor cap,
Then mark the location of that terminal on the distributor base so you know where the #1 plug terminal is when the cap is off.

Flip the distributor cap, and have a look at the rotor.
It should be pointing (ROUGHLY) at the mark you made for #1 terminal on the distributor base.

If it's NOT pointing at the mark you made, you have a problem with where the distributor is set, and you need to lift the distributor and correct for #1.

Once you do these simple things,
VERIFY Compression,
VERIFY TDC,
VERIFY Balancer,
VERIFY Distributor,
You don't have to worry about the IGNITION anymore!

MUCH better to waste 20 minutes to VERIFY the ignition than to wonder if that is the problem or not!
 
#15 ·
carb

i got a 500cfm 2bl sitting on a built 350 chevy in a cj5 i think maybe the compression was to high it burns rich , why would ya need 4bl carb and a passing gear in a jeep but im 3 speed , just a saturday night cruze with big cam , jet it down but lean is bad news!
 
#19 ·
i got a 500cfm 2bl sitting on a built 350 chevy in a cj5 i think maybe the compression was to high it burns rich , why would ya need 4bl carb and a passing gear in a jeep but im 3 speed , just a saturday night cruze with big cam , jet it down but lean is bad news!
Didn't see a 'Question' in there...

If it's 'Rich', when is it 'Rich'?
When it's idling?

Over 'RICH' can also be float level being too high and forcing fuel into the idle and main jets...
Make sure you adjust the fuel/float level before you start messing with idle mixture...

If it's 'RICH' at idle, lean out the idle mixture a little with the idle mixture screws,
And check to make sure the power valve isn't blown while doing so.

Use vacuum gauge as described before to set idle mixture correctly.

If the 'RICH' happens when you are above about 800 RPM, then the problem is main jets being too big,
or it's a power valve opening point problem.

Power valve is EASY to determine what you need with a vacuum gauge,
And smaller jets are EASY to install.
 
#20 ·
I don't agree.
I say to VERIFY the igntion, since it's the easitest to check out....

VERIFY Compression,
VERIFY TDC,
VERIFY The Balancer is correct,
VERIFY The distributor placement,
Then you don't have to worry about ignition...

Besides, it sounds like the distributor is working correctly for centrifugal advance,
he's getting about the correct amount of advance,
And correct advance timing if the engine speed is moving up to over 1,000 RPM...

I'd start with ignition, VERIFY the ignition,
Then move to the carb again...
 
#21 · (Edited)
Hmm, good info.
I never thought about it before - that the side pivots would be superior. But I see your point. The center of the rounded float will "see" the average fuel level anyway, and the roundness keeps it more in balance. And the plus -- jet extensions and the inside vent extensions (whistle) would clear fine, eliminating the need for the notched center floats.
KISS!

The outside vent or "bridge" as we called it, made from copper tube or brake lines - always gave that custom look - I wonder why it took Holley so many years. It's not just good for off road, but road courses too.

The biggest problem, other than the carb itself malfunctioning or put together wrong, was guys putting a huge carb, like a 1180 on a small motor like a 283.

Sure would be nice if it was that easy to modify a FI - without getting into the computer and fuel mapping. That's a whole different world.
 
#22 ·
Hmm, good info.
I never thought about it before - that the side pivots would be superior. But I see your point. The center of the rounded float will "see" the average fuel level anyway, and the roundness keeps it more in balance. And the plus -- jet extensions and the inside vent extensions (whistle) would clear fine, eliminating the need for the notched center floats.
KISS!
Low RPM engines don't need the huge fuel flow tract of the Center Pivot float bowls either.
Unless you are SERIOUSLY RACING a big block for all it's worth,
The side pivot bowls are just fine!

With the added benefit of being better at off camber fuel metering,
AND,
They are MUCH easier to work with in regards to fuel lines, ect.

If you are going to take the float bowl off 40 times a weekend to change jets at a race track, the transfer tube can get quite annoying with side pivots,
But if you are only doing it ONCE or Twice to tune jets/power valve and then leaving it alone,
They ROCK!
----------------------------------------------------------

The outside vent or "bridge" as we called it, made from copper tube or brake lines - always gave that custom look - I wonder why it took Holley so many years. It's not just good for off road, but road courses too.
I wore my hands RAW one summer making polished stainless steel versions of that raised vent line!
Made some GOOD MONEY from it, but I had a hand grip at the end of that summer that would crush about anything!

I first saw that on a farm truck when I was about 10 years old, around 1970, and I though it was a good idea.
The farmer was making his carb run when the truck was inclined to dump the load...
When it didn't have a dump bed!

Copper is MUCH easier to work with,
And if you have slash cut tubing inserts in your vents, you can use RUBBER FUEL LINE!
That REALLY makes it easier!
-----------------------------------------------

The biggest problem, other than the carb itself malfunctioning or put together wrong, was guys putting a huge carb, like a 1180 on a small motor like a 283.
YUP!
Don't know how many Holly Dominators I've seen installed on small blocks with the owner bitching about the engine not 'RUNNING RIGHT'!

Without getting into a long math equation that will lose about everyone reading this,
A 258 CID engine should need a carb around 240 to 290 CFM carb. (with a rough rev limit of 3,000 RPM)

A 304 V-8 with 4,500 RPM Rev limit should only need about 450/500 CFM.

A 360 with same 4,500 RPM rev limit should only need 500/550 CFM carb...

(math, so run now!
Engine displacement, Say 304,

304 CID ÷ 2 = 152 CID per Crankshaft Revolution (4 stroke engine)

152.0 CID X 0.85% Cylinder Volumetric Efficiency = 129.2 CuIn per Engine RPM.

129.2 Corrected CID X RPM Rev Limit of 4,500 RPM = 581,400 Corrected CID per RPM.

581,400 ÷ 1728 (1 Cu.Ft.) = 336.45833 CuFt per Minute (CFM) Rounded to 336 CFM.

Add 100 CFM for over rev, free rev, and for faster RPM gain when loading the engine to maximum,
336 CFM + 100 = 436 CFM.

The closest 'Larger' carb sizes you are going to find is a 430, 450, 500.

Current production 4 barrel 'Off Road' carbs are 470 CFM, 670 CFM & 770 CFM models.

Current production 4 barrel 'Street' carbs are 390 CFM, 465 CFM, 600 CFM, and up...

Current two barrel carbs are 350 CFM and 500 CFM.
-----------------------------------

Sure would be nice if it was that easy to modify a FI - without getting into the computer and fuel mapping. That's a whole different world.
When I worked for DFI, we were working on a system that had sets of dials on it.
You chose one of 4 or one of 5 different RPM ranges,
And you richened up or leaned out the fuel mixture simply by turning the dial in the appropriate RPM range.

We were even looking into adding adjustments for load in those RPM ranges when Accel purchased the company and killed the project so it wouldn't compete with their versions.

We called it 'Fuel Injection For Dummies'...
And that was before the 'For Dummies' books were out,
this was back in about '84 or '85.
 
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