Carb tuning help

[j69302]

I have a holley 600cfh vac/secondaries.

I set the timing to about 14 initial. Idle in gear is about 800. I adjusted the idle mixture with a vacum gauge and it read about 18 inches of vacum.

It runs a little rich at idle. When I rev it quickly in park it seems to stutter a little bit before it takes off. If I rev it slower it responds a little better. Is this too much or not enough gas from the accelerator pump?

I live around 1000 feet, and sometimes drive to work which is around 3000 feet where the sypmtons are more exaggerated. I would like to try to fine somewhere in between where it run good. Up at the higher altitude it is quite a bit slower off the line and stutters worse.. Back down where I live, it runs pretty good, but a little rich even off idle.

Would this be the accellerator pump or should I try some different vac secondary springs?

I also want to check to make sure I have to correct power valve. What size should I need? Ive read that you take you vacum and cut it in half, that would mean I need a 9. I also heard that you take the vacum and subtract 2. that would mean I need a 16. I dont know what one to go with. Holley's instruction manual with the carb says most engines should use a 6.5 to 10 for stock to high performance. And 3 - 5 for engines with radical cams.

My engines specs
302, crane energizer 260 cam, edelbrock performer rpm heads and air gap rpm intake manifold with headers.

I dont know much about tuning carbs but I would like to fix these problems. Any help would be appreciated

 

[ratio411]

I have a holley 600cfh vac/secondaries...

When I rev it quickly in park it seems to stutter a little bit before it takes off. If I rev it slower it responds a little better.


Is this too much or not enough gas from the accelerator pump?

Zeroing in on this statement...
You describe revving it in park.
Does it do the same in gear from a stand still?
I assume it does.

To address your question about changing the secondary spring:
NO
The secondary shouldn't even open when revving in park.
It is only designed to open under heavy load, therefore when you are driving.

Your problem is in the accel circuit.

What have you done with that circuit?

 

[ratio411]

I also want to check to make sure I have to correct power valve. What size should I need? Ive read that you take you vacum and cut it in half, that would mean I need a 9. I also heard that you take the vacum and subtract 2. that would mean I need a 16.

There is a more accurate way of testing vacuum for the PV, however it requires you and a buddy driving the car with the passenger holding a vacuum gauge that is ran into the cabin. I won't go into all that...

The 18 you have should be fine.

The way I was taught to get a good streetable match was to take that number, cut it in half, then minus 2. Basically seems like your two sources each gave you half the method I was taught.
Basicly you end up with 18/2=9-2=7
Therefore 6.5 or 7.5 would work fine.
6.5 is stock in those carbs.

 

[j69302]

Zeroing in on this statement...
You describe revving it in park.
Does it do the same in gear from a stand still?
I assume it does.

To address your question about changing the secondary spring:
NO
The secondary shouldn't even open when revving in park.
It is only designed to open under heavy load, therefore when you are driving.

Your problem is in the accel circuit.

What have you done with that circuit?

Yes it does it in both park and while in drive from a dead stop. I can control it by feathering the throttle. It gets even worse when im up at a higher altitude. The reason I thought about changing the spring in the secondaries was at the higher altitude it was running too rich, thus having the secondaries open sooner would balance out the mixture.

I had another carb of the same kind with a broken base plate and took that power valve(dont remember what the size was) out of that and put it into the carb thats on the car now. In order to get the front bowl of I remember having to mess around with the accel pump spring and linkage. Ive played around with the preload on the spring and gotten it a little better but it still is off a little bit.

I just pulled my plugs and this is what they look like. The last time I drove this was home from work which is about 70 miles on the highway the whole way, so this should show me my jetting?

 

[ratio411]

Looks lean to me...

Edit:
It is hard to tell is what I am getting at with the shrug.
If I had to say, it looks lean, however there is a glare.
It could be fine, and is in no way rich.

Your accel pump should release fuel from the squirter with the slightest of touch on the throttle.
Take the air cleaner off, look at the squirter, see how much the throttle moves before you see fuel come out.

With the carb totally at rest, the arm that rests one end on the cam, other end on the pump lever... That arm should have no play in it. It should touch the pump lever and the cam at rest. THE PUMP LEVER MUST NOT BE DEPRESSING THE DIAPHRAM AT ALL THOUGH. Everything should be tight, at rest, and neutral.
If too tight, the diaphram will be partially depressed, if any play at all, the throttle response will be less than perfect.

Check your pump cam... cam #330 works best.
It has 3 holes, use hole #1.
The throttle linkage has 2 holes to mount the cam, use hole #1 there too.
If the cam is positioned wrong, you can have a delay in the pump action, even if all the play is out of your linkage.

Check your squirter size...
The size needed depends on MANY factors... For a baseline, 25 to 28 should be fine.

Have you had the carb apart much?
How old is it?
What is the list number, including the number after the dash? ( - )
Does it have a rubber umbrella under the pump housing, or a captured BB.
If you have ever had the squirter off, did you put both gaskets back?
Did you return the check valve to the hole under the squirter?
Does your accel pump housing ever leak fuel onto your intake?

 

[gsxrken]

I also want to check to make sure I have to correct power valve. What size should I need? Ive read that you take you vacum and cut it in half, that would mean I need a 9. I also heard that you take the vacum and subtract 2. that would mean I need a 16. I dont know what one to go with. Holley's instruction manual with the carb says most engines should use a 6.5 to 10 for stock to high performance. And 3 - 5 for engines with radical cams.

The Holley site recommends the following for power valve sizing:
"The power enrichment system supplies additional fuel to the
main system during heavy load or full power situations. Holley
carburetors utilize a vacuum operated power enrichment system
and a selection of power valves is available to “time” this system’s
operation to your specific needs. Each Holley power
valve is stamped with a number to indicate the vacuum opening
point. For example, the number “65” indicates that the power
valve will open when the engine vacuum drops to 6.5" or
below. An accurate vacuum gauge, such as Holley P/N
26-501, should be used when determining the correct power
valve to use. A competition or race engine which has a long
duration high overlap camshaft will have low manifold vacuum
at idle speeds. If the vehicle has a manual transmission, take
the vacuum reading with the engine thoroughly warmed up and
at idle. If the vehicle is equipped with an automatic transmission,
take the vacuum reading with the engine thoroughly
warmed up and idling in gear. In either case, the power valve
selected should be 1/2 the intake manifold vacuum reading
taken. EXAMPLE: 13” Hg vacuum reading divided by 2 = 6.5
power valve. If your reading divided by 2 lands on an even
number you should select the next lowest power valve. EXAMPLE:
8” Hg vacuum reading divided by 2 = 4 power valve.
Since there is no #4 power valve you should use a 3.5."
http://www.holley.com/data/TechService/Technical/power_valves.pdf

With regard to your stumble, I agree the answer likely lies in your accelerator pump like the other poster suggested, whether the adjustment, shooter size, or cam position. PS- I've had better success upping the shooters into the low -30s versus tweaking cams or cam positions, but your mileage may vary.

 

[brianj5600]

Check your pump cam... cam #330 works best.
It has 3 holes, use hole #1.
The throttle linkage has 2 holes to mount the cam, use hole #1 there too.
If the cam is positioned wrong, you can have a delay in the pump action, even if all the play is out of your linkage.

Isn't the 330 one of, if not the most aggressive cam? To me it sounds like a rich condition when the accelerator pump is in operation. If it is rich, more total lift and steeper ramp would make it stumble more.

j69302, what color cam is on the carb now?

 

[j69302]

With the carb totally at rest, the arm that rests one end on the cam, other end on the pump lever... That arm should have no play in it. It should touch the pump lever and the cam at rest. THE PUMP LEVER MUST NOT BE DEPRESSING THE DIAPHRAM AT ALL THOUGH. Everything should be tight, at rest, and neutral.
If too tight, the diaphram will be partially depressed, if any play at all, the throttle response will be less than perfect.

I just readjusted the preload on the spring. There was a little bit between the follower and the cam. I loosened the spring one flat at a time until there was no play between the cam follower and the cam.

Your accel pump should release fuel from the squirter with the slightest of touch on the throttle.
Take the air cleaner off, look at the squirter, see how much the throttle moves before you see fuel come out.

Throttle moves approx 10 degrees(I had to eye-ball it and estimate, not sure how to measure this) before fuel comes out. The cam is either red or purple, I cannot not tell and I noticed holley has both a red and purple. it is a lighter color, so Im going to say its the purple one. I also beleive I just barly made out 3 holes, and the only 3 holed cam I saw on summit was the purple one. You can just barely see the color of the cam by looking through hole #2 on th picture below.

If about 10 degrees or so is not correct, then the cam must have a late opening because the follower does not move until about 10 degrees. However, once the follower starts to move, fuel does start to come out of the squirter. I beleive I can also lossen the spring some more, which should inscreas the distance between the pump lever and the spring seat of the follower. This should slightly depress the pump, and I should be able to make it work instantly.

Check your pump cam... cam #330 works best.
It has 3 holes, use hole #1.
The throttle linkage has 2 holes to mount the cam, use hole #1 there too.
If the cam is positioned wrong, you can have a delay in the pump action, even if all the play is out of your linkage.

See the attatched picture below. the cam is looks like there is a screw through a hole labled 1. However, I could not find what you meant about which hole mounts the throttle linage too. Maybe you can tell by the picture.

Check your squirter size...
The size needed depends on MANY factors... For a baseline, 25 to 28 should be fine.

There looks to be a "31" stamped on the squirter.

Have you had the carb apart much?

The only time I ever went inside the carb was to replace the powervalve.

How old is it?

Maybe about 7 years.

What is the list number, including the number after the dash? ( - )

Grabbed these numbers from the front of the Choke Horn.

80457-2
0711

However, the sticker on the box says 0-80457-S. Am I correct to say that this is a 4160 based carb?

Does it have a rubber umbrella under the pump housing, or a captured BB.

Not sure what you mean, it looks similar to the vac. sec. diaphragm housing but smaller. Does this make sense?

If you have ever had the squirter off, did you put both gaskets back?
Did you return the check valve to the hole under the squirter?
Does your accel pump housing ever leak fuel onto your intake?

Never taken a squirter off so the gasket and valve should be good. And there are not leaks.

the carb is "straight out of the box." Except for the power valve which i replaced.

Aside from the accell pump issue, would it be worth increasing the sizing of the jets a little based on the way my plugs look? I know there was glare on the picture but you can still see how white the ground strap and insulator were. Or is this a incorrect plug heat range?

This brings me to another question, I saw in the holly instructions that the carbs secondary metering block is the equivilant of #70 jets. Does this mean that only the primaries use jets? and that the secondary would be fixed because of the block?

I thank you all for the responses.

 

[D.Hearne]

Dave's got you on the right track with the stumble. It's a lean condition doing it. It's very hard to get a single pumper (vacuum sec. Holley) to be too rich from the accellerator pump. The 80457 is the same carb as a list 1850 but has the Ford kickdown lever for the transmission. 600 cfm. The secondary side has a metering plate, no jets. Jets only on the primary side. Only other thing I can think of since you said you've only messed with the powervalve is did you get the gasket under the valve centered correctly when you screwed the valve in place ? It's easy to get this gasket off centered when doing so.

 

[D.Hearne]

You might also get a better pedal feel and response by moving the pivot ball up to the hole above it. The hole above where you have yours is where I always put mine.

 

[ratio411]

DH is right.
Move your linkage to a higher hole.
They make bushings to use the large top hole, but if you don't have a bushing, the next hole up will work.

The cam looks to be the 330.
It is in the linkage position #1, good.
330 is the only cam that I am aware of with 3 settings.
Looks like it is in cam position #1 or #2... #1 is where you want it.
31 is a little big on the squirter, but not huge... you should be fine to get the other bugs worked out. One problem at a time!
The linkage should be tight, like I said, but make sure it does not depress the diaphram.
Tight and touching is fine.
If all this is worked out, then you may have an issue in the pump itself.
If fuel doesn't start to dribble right away, something is out of adjustment.
I don't know what your idea of 10* is.
Tuned well, you can just about wiggle the throttle and cause some fuel to show itself from the squirter.
Remember that if fuel does not come instantly, then what you have is a big hole in the throttle response, until fuel does come.
Stumble that occurs with the movement of the throttle is ALWAYS the accel pump.
And is always lean!
Rich on the accel pump does 2 things:
1: Produces a puff a black smoke, when, and only when the throttle is moved.
2: Produces a stumble the instant the throttle becomes fully depressed, not while being depressed.

#1 is too big a squirter.
#2 is the accel pump circuit running out of fuel before the main circuit can kick in.
Too small a pump cam, too small a accel pump, or too large a squirter can produce #2. An over tight accel pump linkage can cause this too.

They can happen together or individually.

If all this is sorted out, you need to look for the problem a little deeper.
You are running out of fuel, or not getting fuel quick enough, one or the other, WHEN the throttle is in motion.

Deeper problems:
Leaking accel pump diaphram.
Trash in the accel pump fill hole (in the bottom of the fuel bowl) keeping pump from filling properly.
Trash in the accel pump discharge hole, keeping the squirter from getting fuel right away.
Bad umbrella valve under the pump diaphram... This will send the first part of your pump shot back into the bowl instead of to the squirter.
A BB valve is less responsive and will do the same thing to an extent. A BB will never be as responsive than an umbrella type bowl, however it still should not produce a stumble.

This is the long version of accel pump tuning...

Edit:
I feel kinda dumb here, I should have asked you this first...
What rear gear do you have?
What tranny do you have?

If you have a gear lower than say 3.50, you just might need a bigger squirter.
When I run 4.11s in my Maverick, I have best luck with a 36.
Squirter size has more to do with rear gear ratio and car weight than anything else. So if your engine is prone to rev and move out really fast when under load (light car and low gear), your accel pump circuit needs to get the fuel in fast because the main circuit will pick up the slack very fast.
A small squirter is to take up the slack for a slower revving engine or heavier car that will take longer to start the main circuit flowing.

Even though I would like that info, I still don't think it is the problem because this issue shows itself more on the back end of the accel pump instead of on the front.... You have a problem on the front if fuel doesn't flow instantly.

Again, the squirter size can be addressed after the initial stumble.

 

[j69302]

Is re positiong the cam just loosening the one screw and position it and re install the screw?

Ill try moving my throttle cable sometimes today also.


It was a while a go when I did the powervalve, but im 99% sure that the gaskets are on correctly.

I have th 2.79 rear end with a C4. I didnt have this problem until I changed the powervalve.

 

[brianj5600]

One thing confuses me. Why does it get worse at 3000' above sea level? Carburetors seem to get richer as you go up in altitude. Same amount of fuel + less air = richer. That clue led me to think rich.
The lack of arm movement at first is something that needs fixed. The problem may go away if that is fixed.

 

[j69302]

How long to the acell pump cams last? I said the carb is about 7 years old, but Im not sure how many miles is on it.

With the accel pump lever and spring having no play in it and having to move the throttle a little before fuel started coming out, I decided to take a look at the cam for wear. I pulled the cam off and was able to verify that it was installed on hole number 1. I also noticed that the cam follower looks like it was only contacting only half the width of the cam. Looking length-wise on the surface of the cam you can see its lossed about half a mm of material and its actualy sloped. this looks like it could be the area where no fuel would come out of the squirters.

I drove this car for a long time as a daily driver just on the city and short freeway runs and the area on the cam does look like its consistant where the low throttle wear on it would be.

Im going to replace the cam and see if its any better.

 

[j69302]

Ok.. I ordered a cam kit, a jet kit and a vac. secondary spring kit.

I used the 330 cam on hole number one like the carb originally had, and it still had the flat spot before the accell pump lever moved, so I moved the cam to hole 2, and now I get fuel right away like suggested, and it doesnt bog any more when I rev or hit it hard.


So i started playing with the jets and vac sec spring. I went from 65 to 68 main jets, and went from a black to brown vac secondary spring. I can notice that it pulls a little harder now.

When I get some more time or try to fine tune it.


I do have another question about power valves though. I took a look to see which one i had, and im not sure which one it is. The numbers were layed out like this on the metal nut like portion on the back of the valve.

....6
G......5
....8

Im not sure what size this is suppoed to be. These were the only markings on it, and this was taken from a spare holly 600 vac sec.

I appreciate everyones help here. I learned a little bit about carbs and the cars running better.

Thanks.

 

[fasttback]

If you have a gear lower than say 3.50, you just might need a bigger squirter.
When I run 4.11s in my Maverick, I have best luck with a 36.
Squirter size has more to do with rear gear ratio and car weight than anything else. So if your engine is prone to rev and move out really fast when under load (light car and low gear), your accel pump circuit needs to get the fuel in fast because the main circuit will pick up the slack very fast.
A small squirter is to take up the slack for a slower revving engine or heavier car that will take longer to start the main circuit flowing.

Even though I would like that info, I still don't think it is the problem because this issue shows itself more on the back end of the accel pump instead of on the front.... You have a problem on the front if fuel doesn't flow instantly.

Again, the squirter size can be addressed after the initial stumble.

Ratio411 I'm not bashing or picking on you, but this was my belief too before I solved my hesitation off the line (personal experience with testing). My Holley 600 VS ran fine behind a 289 '66 with 3.00:1 rearend. With just changing the rearend to 3.50:1 the car started hesitating off the line, so naturally I up the squirters and played with pump cams (thinking this was right because I was moving faster). The more squirt and/or profile I gave the carb the hesitation got worst. Went to the smallest squirter Holley made (I think 26) and one of the smaller profile pump cams and it solved the problem.

With just the rearend change the car became more fuel efficient "city driving" (better gearing), but less efficient "highway driving." This was the case with my setup and, of course, other setups will vary. Under other conditions these cars may need a bigger squirter and/or pump cam.

 

[fasttback]

How long to the acell pump cams last? I said the carb is about 7 years old, but Im not sure how many miles is on it.

With the accel pump lever and spring having no play in it and having to move the throttle a little before fuel started coming out, I decided to take a look at the cam for wear. I pulled the cam off and was able to verify that it was installed on hole number 1. I also noticed that the cam follower looks like it was only contacting only half the width of the cam. Looking length-wise on the surface of the cam you can see its lossed about half a mm of material and its actualy sloped. this looks like it could be the area where no fuel would come out of the squirters.

I drove this car for a long time as a daily driver just on the city and short freeway runs and the area on the cam does look like its consistant where the low throttle wear on it would be.

Im going to replace the cam and see if its any better.

With a 7-year old carb and a worn pump cam, replace the pump diaphragm too while you are at it.

 

[ratio411]

went from a black to brown vac secondary spring. I can notice that it pulls a little harder now.

Glad you're getting it worked out!
Good to see you getting the courage to dig a little deeper too!
You'll be a master Holley tuner before long.

The PV sounds to be a 6.5... They have an 8 on them too for some reason.


On the black and brown springs:
The black spring won't even open fully. So another spring will feel better.
The brown spring is only a little more than the black.
I am not sure, but I think the 'clear', or unmarked, spring is the next step up.
Your kit might tell you.
The brown is still considered a very restrained spring like the black.
Try the next step and see how it feels.

Dave

 

[D.Hearne]

The Power valve is a 6.5. Go for the gold and install the lighest spring and then go up on pressure till you find what you want. The purple is the next to lightest and the one I use the most. With it on a roller 5.0 (about the equivalent of a carbed Explorer 5.0, with the same cam but ported E7 heads) the secondaries would come in about a second or two after nailing the pedal.

 

[jlangholzj]

there should be a clearance of .015" between the accel pump arm (comming out of the bottom of the front dish) and the spring bolt. little late, but theres my 2 cents

very helpful:

http://www.junkyardgenius.com/holley/hol01.html