[texasimport]

Ok. . .bought my first CJ back in Sept. The PO had just added a HEI dist, Holley 470TA, edelbrock performer intake. It ran eye watering rich and I did a lot of tuning made it much better but, couldn't remove a stumble issue under medium throttle, even talked with holley tech support . The Holley guy said the 470TA was not meant for a 304 and he offered me a 670TA. I took the bait.
Now a couple months later I get the engine rebuilt, 40 over, off road cam, heavy valve springs, balanced, edelbrock shorty headers.

Now we work to tune this thing properly. I borrowed an exhaust gas analyzer, very nice and have the following set up.

Power valve 75, vacuum = 15 ish
Mains 59 secondaries 64
squirt nozzle 41
Acel pump cam ooober black one, rolls in the fuel hard and heavy
Float levels set so it just dribbles out if you rock it a little.

Timing, about 9 idle no hook up and ends up at around 37.
Using manifold vacuum although can't hardly detect a difference if I use ported vac.

Fuel, using the stock filter with return line setup. Yes the filter is placed high in the system and the return line is on top. Using a holley regulator and am showing about 5 for fuel pressure. No charcoal canister but the tank is vented.

So before rebuild the stumble would be ~2500 RPM mid throttle. Chaulked it up to tired motor. Now post rebuild with a 670TA instead of the 470TA I now have much less stumble and now it is a much lower RPM, just off idle, acel pump circuit. Started with orange cam and 28 nozzle and have made most of it go away with current settings but not all. More pronounced when cold. The analyzer shows I am going a bit lean during transition from idle to mains. The nozzles are so big now that my 30 CC pump does not take long to empty. I was toying with going to a 50CC pump but I was told that is pretty uncommon to need the bigger pump capacity on a 304.

I almost think that the 670TA recommended by Holley tech support is a bit big and the stumble may be related to my primary venturies (SP?) being so big that when I am transitioning from idle to mains I am not getting enough signal, vac to pull enough fuel soon enough.

HELP. . . . . .

Soon as I can save a few I will be converting over to EFI but that is months away yet.

[JeepHammer]

The 470 was fine for a 304 that wasn't going to turn high RPM's,
And since it has smaller venturi bores, it would have given better throttle response and fuel metering.

Most of the Holley (or any carb switch) tuning problems are usually improper install.
Vacuum leaks, off brand gaskets plugging up vacuum ports on the base plate of the carb,
Tightening down carb throttle plates to the intake with too much force bowing the base plate,
Not having any slack in the throttle linkage/cable so the throttle blades can fully close,
Not having the throttle cable pull the main bores open to vertical so the secondaries get full vacuum and work correctly, ect.

ALWAYS make sure there is slack in the line when at idle.
Doesn't take much, but the slack needs to be there.

ALWAYS make sure the THROTTLE PEDAL opens the primaries FULLY VERTICAL when pressed to the floor.
You can't tell if the throttle blades are going vertical by just working the linkage at the carb,
You MUST adjust so the PEDAL makes the blades go vertical.

ALWAYS make sure you linkage is correct so the blades aren't pulled over center, as in PAST vertical!
Again, this screws up the primary venturi signal and causes problems.

ALWAYS check for vacuum leaks!
Over-tightening the carb to manifold will create vacuum leaks as the carb heat cycles on the engine, so you have to watch for that.

ALWAYS Make sure you check for unused vacuum nipples on the baseplate of the carb, manifold, signs of leaks from cracked/stretched hoses, ect.

ALWAYS use 'Holley' brand gaskets,
They are cut correctly so the vacuum ports on the bottom of the carb are covered/uncovered correctly,
And they compress more evenly so they don't cause High/Low spots when compressed.

ALWAYS check the accelerator pump linkage.
You should start getting 'Pump Shot' IMMEDIATELY when the throttle starts to open,
And when the throttle is fully opened, the relief spring (Spring around a bolt that works the accelerator pump arm) is adjusted so you have at least 0.030" of clearance between pump arm and adjustment (bolt head).

That way you don't bottom out the pump and damage the valves/diaphragm or bend the arm.
.......................

Running engine checks.

ALWAYS gauge your fuel pressure before it enters the carb!
Between filter and carb inlet if at all possible!
Holley works best around 5 PSI of fuel pressure,
But will 'Tolerate' anything between about 4-7 PSI.

If you have too much or too little fuel pressure,
Time to fix that NOW!
You won't get accurate readings or adjustments if you don't.

ALWAYS check the float level when you start the vehicle.
Float level is critical, and you MUST adjust it correctly.

ALWAYS make sure your INITIAL TIMING is set correctly before you try to set idle mixture.
Timing effects vacuum signal greatly, and changing timing often means an adjustment to the idle mixture.

ALWAYS adjust the IDLE MIXTURE screws EVENLY.
You will find one on both sides of the front metering block.
Start with them both bottomed out (GENTLY! Don't crank down on them when bottoming them out)
Back out about 3 turns EVENLY,
Then EVENLY adjust them in TOGETHER, until the engine LOOSES about 500 RPM, or you reach the highest STEADY vacuum reading.

ALWAYS make sure the idle SPEED (Curb Idle) is correctly adjusted.
Idle mixture will effect idle speed, so Idle mixture is set first.
Idle Speed (Curb Idle) DOES NOT effect idle mixture, so it should be corrected last.
------------------------------------------

Once you have the idle mixture, speed, linkage, and float adjusted, it's time for some driveability adjustments...

ALWAYS make sure you remember to hook up the distributor vacuum advance,
(Which has to be unhooked/plugged during initial timing check/correct)
Make sure you connect it to the SPARK PORTED VACUUM source.
That would be the vacuum nipple sticking out of the passengers side of the metering block.
(Adding vacuum advance to the ignition might require you to correct the idle speed again)

ALWAYS make sure the accelerator pump delivers about a two second fuel shot to the venturis.
This is the enrichment fuel needed to sustain the engine while the carb is transitioning from idle circuits to main jets.

If you get a 'Stumble', 'Bog', 'Lag', or 'Hesitation' when you push down on the throttle from a standing start,
You don't have enough accelerator pump shot delivering fuel to the venturis.

Hooking your vacuum advance to 'Manifold Vacuum' will often cause a 'Stumble' or 'Bog' off idle, so be aware of that if you have a distributor that recommends a manifold vacuum source over a spark ported vacuum source.

When you are driving the vehicle,
You will need to hook up a vacuum gauge to the intake manifold, or to a full base plate vacuum signal source...

Take a vacuum reading when you are at Part Throttle Cruise (PTC)...
Moving about 55 MPH on flat land, with STEADY THROTTLE,
Take that vacuum reading...

Most of you will be around 9 or 10 In.Hg. vacuum on that reading.

ALWAYS install a 'Power Valve' about 2 In.Hg. vacuum BELOW your PTC vacuum reading for highway operations.
2.0 In.Hg. is a VERY GOOD opening point for enrichment,
It will give you extra fuel when you try and make slight pedal changes for keeping up with traffic without dumping fuel all the time,
Or being late opening, which can cause a 'Bog' or 'Hesitation' when trying to speed up in traffic or going up a hill.

Serious wheelers will want to install about 2.5 or 3.0 In.Hg. Vacuum opening point Power Valve so the enrichment stays closed a little longer when wheeling.
This prevents the vehicle from 'Jumping' with slight throttle changes when trying to negotiate obstacles, but still give you good highway manners.

Guys wanting to 'Hot Rod' a Jeep will want to lessen the vacuum differential between PTC vacuum signal and opening point.
They will want to run about 1.5 In.Hg. below the PTC cruising point vacuum signal.
This will open the enrichment circuit a little faster and give you some extra 'Jump' when you try to accelerate in traffic or go up hills without the throttle being fully open.

KEEP IN MIND...
If you are running a GM HEI distributor, the vacuum advance is much 'Faster' and adds more advance to the timing curve.
Many times (most times actually) you will find the timing is too much for the engine at PTC when you try to accelerate a little for traffic or keep speed up on hills...

If the power valve is correctly sized for the PTC vacuum signal,
And you get a 'Hesitation' or in extreme cases, 'Pinging' or 'Spark Knock' when trying to accelerate slowly during PTC,
Then you have too much ignition timing for the engine load, RPM and fuel mixture.

The only way to 'Fix' this problme is by using the CORRECT vacuum advance source (Spark Ported Vacuum),
And by adjusting the vacuum advance to work with the vacuum signal being used (adjustable vacuum canister on the distributor),
In extreme cases, you will have to limit the amount of advance the vacuum canister can apply to the ignition curve...

....................................

Secondaries adjustment.

VENTURI SPEED/VOLUME is what powers the secondaries,
Not manifold vacuum.

The primaries have to be open quite a ways before the secondaries unlock,
MAKE SURE the linkage between primary and secondary shaft lock (drivers side) is keeping the secondaries locked closed during idle!

Then there has to be quite a bit of air flow through the primary ventures before there is any power to open the secondaries via the vacuum canister on the passenger side of the carb.

To adjust the opening point of the secondaries,
You MUST have the idle, and primaries working correctly.

You can adjust the opening point of the secondaries by changing the 'Pre-Load' spring in the secondary canister.

I suggest you DO NOT mess with that until you figure out the rest of the carb!

Late secondary opening, lighter spring,
Early secondary opening, stiffer spring.

MAKE SURE you get the check ball back in the canister correctly, and MAKE SURE the diaphragm edges are pulled out where they belong and the canister seals up correctly.

MAKE SURE you use a fresh gasket between carb vacuum source boss and the canister vacuum port when you remove/change the springs.

If you have a removable top vacuum canister,
MAKE SURE you lubricate the 'O' ring with a SILICONE based grease and it's in good shape.

Any vacuum leaks to/at the canister, and you won't get proper/repeatable opening!

[crrushing]

Will all these instructions be the same for a 390 4bbl holley?

[texasimport]

Jeephammer. . .many thanks. . .lots of good stuff to read but what stands out to me most is that your method of power valve selection is different from what I learned and makes good sense. I will put my vacuum gage on tonight and see what I get at PTC which I bet is pretty low. That said I bet my power valve may need a change towards the lower end and this is easy for me to justify sitting here in my office that this may help with my transition stumble. I will update soon. . . .

Thanks again.

[JeepHammer]

Originally Posted by crrushing

Will all these instructions be the same for a 390 4bbl holley?

Same for any Holley.
I can't do specific diagnosis because the OP isn't qualified or educated to make the timing, fuel or vacuum maps for me...

It's just common for newbies to take the word of the manufactures...
And what he hasn't realized yet is the guys he's talking to are no 'smarter' or better educated about the tuning than he is!

Not his fault, he simply hasn't had the 'Education' to do this stuff yet,
But he IS getting an education on what it costs in cash, aggravation and time when you listen to the 'Experts' on the phones trying to sell you something!
(We've all been there! )

The phone guys got hired in to read from cue cards over the phone, and they don't have ANY IDEA how the products work, or what changes need to be made to make them work together!
(It's cheaper to fire the old engineers, mechanics and machinists that knew what they were talking about and hire in 'Kids' at 1/10 the cost of 'Skilled & Qualified' labor would cost!)

The OP is NOT stupid, he's NOT lazy, he's NOT cheap...
He was misguided and mis-informed by the people at Holley, DUI, ect.
And frankly, after they sell the product, they could care less if you ever get it working or not!

You WILL screw around with it long enough to be out of warranty most times,
Then you will get frustrated and sell it just to get rid of the problems!

I spent 10 years on the 'Road Show' for MSD, Holley, Blower Drive Service, fixing field 'Issues' at races and car shows,
And I spent another 20 years in my own shop fixing these same 'Issues'...

This was going on a long time before this guy got sucked into this situation,
And it will suck in people long after he's forgotten about this jeep!
---------------------

On the other hand,
I'm glad to help when I can,
BUT...
There is a limit to what I can do over the internet,
And with the information the guys can give me!

Again, it's not their fault!
They aren't claiming to be 'Factory Trained', so often they can't even formulate the questions coherently,
And if they do get the symptoms/question correct,
They may not know how to map out an entire ignition advance curve,
Or how to map out an entire fuel system or vacuum curve!

The guys on the phones *SHOULD* know that stuff,
But usually they don't have any more clue or education than the guy making the call with the 'Problem'...

[JeepHammer]

Originally Posted by texasimport

Jeephammer. . .many thanks. . .lots of good stuff to read but what stands out to me most is that your method of power valve selection is different from what I learned and makes good sense. I will put my vacuum gage on tonight and see what I get at PTC which I bet is pretty low. That said I bet my power valve may need a change towards the lower end and this is easy for me to justify sitting here in my office that this may help with my transition stumble. I will update soon. . . .

Thanks again.

Hope that helps...

Tuning carbs to work with ignitions is the big hurdle.
You REALLY have to know about the pressure differentials that cause both to work to get them working together,
And NEITHER will work without the other.

Power Valves are the 'Big Mystery' in Holley designed carbs,
And there really isn't any mystery to them.

Engine vacuum sucks them closed when you start the engine.

They are there to add fuel in the mid operating range when the accelerator pump is mostly useless because of the RPMS the engine is turning.

When you are at PTC,
The fuel mixture is running off of MAIN JETS ONLY.
When you tip into the throttle just a little,
You only get a small fraction of fuel you need from it since you aren't making any large throttle movements,
And by the time you are fully on main jets (around 1,200 RPM) the little dab of fuel supplied by the accelrator pump is not sufficient to fatten up the fuel ratio enough.

When you tip into the throttle, the manifold vacuum drops,
And if the Power Valve is adjusted correctly (Correctly sized), it will add a fairly large quantity of fuel right away to the primaries.

When you go up hills, the vacuum drops,
And if drops 2 In.Hg. or more, then the power valve automatically opens and adds fuel to get you up that hill.
Closes again when the engine load lightens up to save you fuel...

Pretty simple, fairly ingenious, and automatic when properly sized.
-----------------------

At lower RPM, or during idle circuit fuel,
The power valve does nothing.

At lower RPM, there isn't enough suction from the air going through the venturis to draw any fuel up the power valve enrichment tubes anyway,
(A smaller carb would create more suction faster, so you get better fuel metering response with a smaller carb at low to mid range RPMs)

So at lower RPM, the accelerator pump takes on the duties of putting extra fuel to the engine when you are trying to make the transfer from idle circuit to main jet circuits.

If you pay attention to the accelerator pump cams,
You will see it really pumps a LOT of fuel in the first 1/3 of the throttle stroke, then tapers off to about nothing in the second 2/3 of the stroke.

That means if your throttle is 1/3 or more open (like at highway speeds/PTC) you get virtually nothing from the accelerator pump...
Enter the power valve to the rescue!

You *CAN* Change the cams for the accelerator pump so it delivers less fuel in the beginning, and more for longer period, but still,
It can't do everything at all points of the throttle stroke no matter how you adjust it.

Stumble off idle, in lower gears where the overall drive ratio is favorable... Usually not enough, or fast enough, accelerator pump shot.

'Hestitaion' or 'bog' when trying to speed up from PTC,
In high gear, with heavy drive train loading (unfavorable overall drive ratio/ heavy loaded, low RPM engine),
Almost ALWAYS a combination of too much ignition advance and too little fuel enrichment (Power valve not opening soon enough)...

When you are driving down the highway,
Big tires, 'Highway' gears, you are slowing down the engine considerably,
And large tires pull the drive line ratio down even farther,
So the engine is LUGGING around a lot of weight with bad gear ratio to do it with.

Throw in the main jets ONLY, fuel mixture at it's LEANEST,
And too much advance on the ignition,
And the piston simply doesn't have time to break over Top Dead Center of the crank shaft rotation before the ignition fires the cylinder, cylinder reaches peak pressure too soon,
And tries to force the piston back down the way it came,
Instead of letting it break over TDC and making power on the 'Down Stroke' like it's supposed to.

Add some fuel, and you won't have such a 'Lean' condition, meaning the cylinder will take a few more milliseconds to reach 'Peak Pressure'...
but the most effective way to do things is to take some timing out of the advance curve when the engine vacuum drops from 'Lugging'...

That's as simple as tuning the vacuum advance to respond the greatest amount when you are at PTC instead of like DUI, MSD and all the other 'Hot Rod' companies like to do and give you full advance right off of idle speed!

Switching to 'Spark Ported Vacuum' helps some,
It's more 'Moderated' since it's a mixture of velocity through the carb and manifold vacuum,
Keeping full advance out of things when the engine is loaded,

But mostly you just need to back the darn total timing down when it 'Rattles' 'Spark Knocks', Pings or 'Hesitates/Bogs' at PTC + Tipping into the throttle a little...

Those are all signs of the piston, rod, bearings and crank, not to mention what it's doing to valves/seats! getting hammered senseless when the ignition fires too soon and you hammer the combustion chamber peak pressure WAY too soon!

Running as much advance as you can SAFELY will save you gas, give you more power, ect,
But when you fire too soon, EXPENSIVE BROKEN PARTS WILL HAPPEN!

Like I said, just trying to help, and if giving you information by the 'Numbers' is any help, you are welcome to it.

If it's too 'Basic', then I'm sorry, but I don't know your skill level, and starting out too basic is better than 'ASSUMING' you know something important later, and you not getting the results you want... Or DAMAGE!

[TKFireman]

Originally Posted by JeepHammer

If it's too 'Basic', then I'm sorry, but I don't know your skill level, and starting out too basic is better than 'ASSUMING' you know something important later, and you not getting the results you want... Or DAMAGE!

This is not too basic, in fact, its way over my head. I have basically the same setup, with a 304, 670 TA, edelbrock performer intake, rest of engine is stock, and a HEI distributor.

I changed the power valve from the stock size of 6.5 to a 9.5, because I was told it needed to be about half of my idle vacuum, which is 20 inhg, haven't checked vacuum while driving. I'll do this when I get a chance, will be a few days, and see what I get. Changing it to a 9.5 helped the stumble I had tremendously, but its still not right

I also have the stock jets 68/89 in the carb because I simply don't understand it enough to know what to change them to, and don't have the tools to test exhaust gases. I'm sure that it is rich, would I be safe to assume that I could use the same jets as teaxsimport, and at least be in the ballpark?

I have the initial timing set at 8 DBTDC, with the idle screw backed all the way out, it idles at around 900 rpm. I fixed many vacuum leaks to get it down that low. If I'm pulling 20 inhg, is that a good indication that I have all the vacuum leaks fixed? Could it be idling a little high simply because the jets are just too big?

I don't know enough about the rest of the adjustable parts to tinker with them. I did set my mixture screws as described until I had reach the highest level of vacuum at idle.

I apologize if I hijacked your thread texasimport, I know we have discussed these carbs before, and I' still trying to learn about them

[texasimport]

TKFiremen. . . keep in mind I live at just under 6000 feet so my settings would be a bit lean for your use. That said use your spark plugs as your gage to determine how rich it is running and I bet you will end up someplace around 64 primaries and 68 for your secondaries.

Couple rules I learned was one size smaller for every 2000 ft. and the secondaries can always be set a bit bigger than your primaries. By the time you actually open those secondaries up you have your foot way in it so rich is not such a bad thing, lower EGTs etc. That's why I keep my secondaries those few sizes bigger

Glad you jumped in. . . I have been wondering why I must be the only person that has been unable to plug in a Holley TA and have it run perfectly. Even had two different mechanics that claimed they new how to adjust Hollys do things that clearly indicated that they know much less than I do which was pretty scary.

[TKFireman]

I spoke to you about it a few months ago when I was playing with it. I got it running ok, but didn't know where to go from here, so haven't played with it anymore. I'm going to check my fuel pressure and my vacuum at PTC as suggested. I will also check the other points Mr. hammer pointed out, but will be Sunday at the earliest before I can mess with it. I also need to call Holley and see if I can get new sight glasses to set the float level with. One is fogged up, and the other is broken off flush with bowl, so can't see through them. They don't leak, so haven't removed them yet. This carb came this way on the jeep when I purchased it. It had vacuum lines hooked up wrong, heater hoses hooked up wrong, ports everywhere not capped, so it took me a while to get it running as good as it does.

I'm around 2000 ft altitude but enjoy driving to the beach and the mountains, which top out around here at about 6000 ft or so. Haven't taken the jeep there, but would like to. Should I keep this in mind while doing this, or just set it in the middle where I am and go with it?

I'm thinking of going ahead and rebuilding the carb, I've been told its fairly inexpensive and not hard, I'm sure to learn something while I'm doing it. At the same time I'll change the jets, probably as you recommended to somewhere in the mid 60's. What about the pump discharge nozzle, which I assume is what you called the squirt nozzle. According to Holley, the stock size for mine is .028, and I have the stiffer black secondary spring. I have no idea what pump cam I have, or how to find out. Would you recommend changing either of these at the same time? Any other parts to tweek at the same time when I rebuild it, or should I do all these one at a time to see what change it makes?

[crrushing]

Hammer,
Would you recomend a permanent fuel pressure on all rigs or just particular ones?

[crrushing]

sorry i meant fuel pressure regulator

[texasimport]

Originally Posted by TKFireman

I'm thinking of going ahead and rebuilding the carb, I've been told its fairly inexpensive and not hard, I'm sure to learn something while I'm doing it. At the same time I'll change the jets, probably as you recommended to somewhere in the mid 60's. What about the pump discharge nozzle, which I assume is what you called the squirt nozzle. According to Holley, the stock size for mine is .028, and I have the stiffer black secondary spring. I have no idea what pump cam I have, or how to find out. Would you recommend changing either of these at the same time? Any other parts to tweek at the same time when I rebuild it, or should I do all these one at a time to see what change it makes?

TKFiremen. . . . .yep the stock nozzle/squirter etc was as you suggest .028 on mine. Yes I went a few steps at a time bigger to try and help with the off idle stumble. Only cost about $6 so go get a 32 or so and see what it does. Just be careful you don't drop either of the two little washers down your intake when you change it. Yes it helped but also worked the colored cams for a while too.

Pump cam can be found just behind the throttle linkage. Just follow the acel pump cam arm into the linkage and you will find a little colored plastic cam that tells that arm when and how far to move.

Just to keep you from going nuts. . . . .make only one change at a time.

[jayscj7]

Is a 390 holley carb to big to run on a 258? My 1980 cj7 has an offenhauser intake and a 390 holley on it. When at idle I always smell lots of fuel coming from the exhaust. When I tried to adjust the fuel mixture after warming it up, I shut the fuel mixture all the way down. From my understanding it should have stalled out the motor, but it kept running.. Does this mean that the jets are to big, and would need to be rejetted. Or is there another way to compensate for the rich mixture?

[JDurkin1234]

Wow! This thread may very well be a message from the heavens. I have the same set up and the same problem with the big Holley...and just can't get it dialed in for anything...adjusted the timing/distributor and still can't get it right.

What degree are you running your dist? my manual says b/n 4-6 but I've read elsewhere 8 works better.

[texasimport]

I have been bumping around 8-9.