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post #1 of (permalink) Old 05-07-2009, 10:45 PM Thread Starter
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Holley Carb ?'s

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.
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post #2 of (permalink) Old 05-08-2009, 05:44 AM
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welcome to the board!

I don't remember the poster you're talking about. Do a search to see if you can find the thread you're talking about. "Crand cam" is not a common phrase. It might find the thread for you.

EVERYTHING's easy for the guy who doesn't have to do it.
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post #3 of (permalink) Old 05-08-2009, 08:56 AM
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Quote:
Originally Posted by mdn86cj7 View Post
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.
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!


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

[b]Fifth[b], 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...

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

[b]Seventh[b],
Make sure your distributor is hooked up to SPARK PORTED VACUUM!
If you don't, your distributor vacuum advance will not function correctly...
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post #4 of (permalink) Old 05-08-2009, 01:41 PM
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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!
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post #5 of (permalink) Old 05-08-2009, 02:56 PM Thread Starter
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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.
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post #6 of (permalink) Old 05-08-2009, 03:06 PM Thread Starter
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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.
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post #7 of (permalink) Old 05-09-2009, 12:45 PM Thread Starter
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Can anybody enlighten me on appropriate vacuum at idle for 258 (keeping in mind a 4.0L head). I've lost my Haynes manual.

Also, since it won't run (except at part throttle) can I trust any vacuum reading I get while cranking it?

Thanks.
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post #8 of (permalink) Old 05-09-2009, 02:33 PM
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Quote:
Originally Posted by mdn86cj7 View Post
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.
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post #9 of (permalink) Old 05-09-2009, 03:26 PM Thread Starter
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Still digesting your post.

Can I use my original metering plate and bowl on the new baseplate and airhorn? The metering plates are both stamped 6293.

Thanks.
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post #10 of (permalink) Old 05-11-2009, 07:43 PM
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Quote:
Originally Posted by mdn86cj7 View Post
Still digesting your post.

Can I use my original metering plate and bowl on the new baseplate and airhorn? The metering plates are both stamped 6293.

Thanks.
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.
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