I just got my 406 going and it is running rich, jetting isn't that far off, or least it shouldn't be. 73pri-86sec stock is 70-85, List is 4780-2. It was running rich on my last 383 as well, which I attributed to large duration and not enough compression. This motor has 12" at idle so I will be putting a 6.5 pv maybe 8.5? I will be going back to stock jetting. However, the chokehorn was milled with some other mods a long time ago so I really can't return it to factory specs. It seems to be rich in idle circuit, and cruise. At 1-1/4 turns on the idle screws. stock heat range plugs look black at the base of the threads and the porcelin. Outside Temp is a consideration so I will jet down a play with it. Any additional advice would be welcomed. SS

I'd try a smaller carb, maybe a 4779, 4778, or even a 4777. Idle circuit is pulling from the air bleeds in the air horn. Main jets is for the main circuit, idle not pulling from there.

Stay with your first choice of PV, 6.5.

Make sure fuel is not dribbling from the venturi boosters. If it is, lower the fuel level.

Looks like you are on the right track going back to stock jetting.

I personally do not worry about it. My plugs look sooty when I pull them every time, and always have. The only way to do a true plug check is run it full out and shut it off immediately then pull them. I don't think the track would appreciate me off to the side of the return road pulling plugs around scalding hot headers so I don't do it. They are not fouling so I don't worry about it. Sure it runs a little rich but i would rather be on the rich side anyway. If you run it right on the ragged edge, you will be constantly changing jetting as the weather changes.

I bracket race every week and there may be .001 or two in the jetting but it's not worth the hassle IMHO.

If you are not racing it regularly and you are not fouling plugs, put it back to factory spec and don't worry about it.

I just checked couple of the plugs and they look pretty clean huh, it did however seem to get a little soggy as I drove it more. It also smelt pretty darn rich pulling it in yesterday. I will change the power valve and hopefully it will be warm outside soon enough to get a good idea. Thanks for the replies. SS

[ 02-10-2005, 06:21 PM: Message edited by: railing68 ]

check the floats! If the float level is high enough to make the boosters leak then it will be rich.

Originally posted by Drag Fabricator:
check the floats! If the float level is high enough to make the boosters leak then it will be rich. I agree with Brian

Stick to the stock jetting for now.

Your plug heat range could be confusing the issue too. Look carefully at the strap and find the color change. If your timing is correct, the color change should be right at the bend in the electrode. If it is closer to the tip then the plug is too cold, if it is too hot the color change will be closer to the base.

The best tuning aid I got was the Innovate wideband O2 sensor setup . On a 4778, I found 1 1/4 turns too much. I wound up around 7/8 turn and my plugs are not sooty. Other areas I addressed was fuel pressure, float level and a loose PV!

Thanks for the replies, looking a #3 plug the color change occurs right at the bend. This is with 16* initial and what should be 34* total. I will double check the total but there is supposed to be 18* centrifugal. One thing as far as the timing goes is vac advance? Dave Ray set up the distributor and taught me how to add more centrifugal if needed later. But to achieve the right amount of total timing now the initial must be at least 16*.

Is this quite a bit for this cam?

Dave SWEARS by running vac advance directly to port vac. Now this is a critical argument. With my old cam/383 it wanted the additional timing at idle-6* in the can. But in speaking with my machinist yesterday he brought up a good point. When connected to manifold vac as soon as you accelerate vac drops and the motor loses timing. He recommended using the ported vac on the metering block which is pretty common for most. SO the timing is right but that included the additional 6* at idle. I don't think this thing needs the additional at idle. I will try both and try to decide. Plug heat range is 26 autolite which is stock heat range, which should be considered pretty hot. I would like to run 25's this spring/summer. The cam makes it sound docile at idle but seems really responsive, so far so good, nothing wrong with a sleeper. :D SS

dont do anything until you check the float levels. They should be at the bottom of the sight plug hole. the clear plugs with an o-ring will give a false reading sometimes as they distort the view.
remove them, and the fuel should be just barely lapping over the sight plug hole threads.

Becareful when setting float levels and checking float levels, its a possible fire hazard (i dont know how familiar you are with carb procedures).

typically if you bump the fender and it just barely comes out they are right. I will check them though. SS

if they're at that point, they're OK. if it pours out, theres a problem.

a bad powervalve will cause it to load up at part throttle, but not idle.

sounds to me like its loading up at part throttle. this correct?

I always pull a vacuum on powervalves to find out if they're good or not. Even new ones. I use one of those little brass sears hand vacuum pumps.

But in speaking with my machinist yesterday he brought up a good point. When connected to manifold vac as soon as you accelerate vac drops and the motor loses timing. He recommended using the ported vac on the metering block which is pretty common for most. SO the timing is right but that included the additional 6* at idle. I don't think this thing needs the additional at idle.

Why would ported vacuum not drop when you accelerate but manifold vacuum will? Where do you suppose the vacuum is generated for the ported setup?

Vacumn will not drop b/c it comes from above the throttle plates and as long as motor is running you should have vacum there. Why dont you eliminate that and work with lock down plates,, put the initial in on crank then the rest thru total and make sure total is limited to only what you want.. If you need total of 36 , limit dist to that and work with crank with differance..could be 12 -14 initial. If someone has taken air horns off , sounds like they may have redrilled air bleeds, Seems like you have lost your starting point and changed to many things at once. You have to get a good manifold signal to make it all work, larger the carb , weaker signal,,, you are getting too much fuel... get back to basics.. Go on line to Holley and they will list correct air bleeds etc.. 750 cfm carb would be largest to run on that motor... you also might try giving motor a little more air,,, by working with back throttle plate stops. If that dont work try drilling small hole in each plate to assist. Cam has lots to do with this too .

Well if the can is giving 6* at idle via from manifold vac, by switching to a ported source the I would not have the additional 6* at idle, Just under a load etc. when the vac signal could add the timing correct? Vacuum reading I got was between 12-13", so I am thinking that is pretty decent. Ideally I would like to have a 750 but, this is the carb I have so I don't really feel like shelling out $ for a 4779 or speed demon just yet. I will check the air bleeds out. I haven't changed anything yet, in terms of what is within my control but I do understand that tuning becomes harder since there is no factory baseline. The jets are what I had in it 73-86. I run a 28 sq pri and 31 sec. There are small holes in the primary blades. Thanks for the help, SS.

My vacuum advance is in the same box with all the other stuff i never use.
Instead why not use a short adv. curve which allows for alot of initial timing and work without the vac. advance variable.

Originally posted by zdld17:
Vacumn will not drop b/c it comes from above the throttle plates and as long as motor is running you should have vacum there.... Could you expand on this theory? I'm trying to figure out how you get vacuum above the throttle plates 'as long as motor is running'. It would seem to me that the vacuum is below the throttle plates, and it is this effect that makes ported vacuum possible.

Earl Parker of Earl Parker Carburetion sent me the following setup memo. We used it on a 4779 Holley used on a 331" road racing motor and it worked very well. I don't think that the 800 cfm 4780 is 'too much carb'.


One method of setting up your idle system is a follows:
To start with, invert the carburetor and check the position of the throttle
butterflies. Turn the idle speed setting screw to set the bottom edge of the
primary throttle butterflies about .020" from the bottom edge of the transfer
idle slot. Don't worry about measuring anything - your eyeball is good
enough. Positioning the throttle butterflies near the bottom of the transfer
idle slot at curb idle is absolutely critical for maximum acceleration.
Next, turn the idle mixture needles in until they are lightly seated. Excessive
force here will damage both the needles and metering block and make the
idle fuel mixture difficult to set with any accuracy. After seating them turn
them out 1 1/4 turns, which is a good baseline setting. Now you're ready to
reinstall the carburetor and setup your idle system.
Before you start the engine, examine the fuel bowl side of the throttle body.
Hopefully you'll see a little tube, covered by a rubber plug. This vacuum port
connects with a passage in the throttle body that 'sees' manifold vacuum.
Remove the plug, attach a good vacuum gauge to the port and position the
gauge where you can see it clearly. Don't forget to zero out the gauge.
Without touching the carburetor, turn the engine over until you have
pumped fuel into the bowls. Work the throttle a few times then start the
engine. If it dies, which is likely, you'll have the turn the idle speed setting
screw to increase the RPM to get it to idle while it's cold. Since throttle
butterfly position is critical, count the turns and fractions of turns so you'll
know exactly where you're at. The whole idea is to be able to return the
throttle butterflies to the position you originally set them at. As the engine
warms up it should gain rpm, so you should be able to reduce the throttle
opening at least somewhat without the engine dying. Now the fine tuning
begins.
With the engine idling, pick one of the idle mixture needles and turn it in 1/4
turn while you're watching the vacuum gauge. Give the idle a few seconds
to stabilize. If manifold vacuum increases repeat the process, letting the idle
stabilize each time, until it starts to decrease. If turning it in hurts manifold
vacuum then try turning it out. When you've found the 'sweet spot' (i.e. the
manifold vacuum is as high as you can get it) repeat the process with the
other idle mixture needle.
Presumably you'll be able to pick up enough idle speed by optimizing the idle
fuel mixture that you can close the primary throttle butterflies down to their
original position near the bottom of the transfer idle slots.
As a final check give each idle mixture needle a slight turn in then a slight
turn out. If any motion hurts manifold vacuum, you know that needle is set
properly. At this point if the idle is stable and the engine responds quickly
when you just crack the throttle, you should be good to go.
One final note: Make sure your timing is set correctly before starting this
process.
If your distributor has a mechanical advance system there is a much better,
though more involved, way to setup the idle system.
Position the throttle butterflies and idle mixture needles as described above,
attach the manifold vacuum gauge to the vacuum port and start the engine.
Turn the idle speed screw to increase the RPM, again taking note of exactly
how much you have to turn the screw to open the throttle butterflies
enough for the engine to idle while it's cold. Allow the engine to warm up,
the close the throttle butterflies as much as reasonably possible without the
engine dying. Attach a timing light, check to see how much initial ignition
advance you have and make a note of the figure.
Next, loosen the distributor hold down clamp and turn the distributor so as
to increase the initial ignition advance. When the initial ignition advance is
increased the RPM should rise as well, allowing you to reduce the throttle
butterfly opening. Simply turn the distributor to increase the initial ignition
advance and continue to reduce the throttle butterfly opening until they're
in the original, correct position and the engine is idling at the desired RPM.
Lightly snug the hold down clamp to make sure the distributor can't move,
then adjust the idle mixture needles for best manifold vacuum. Once they're
properly set if the idle RPM is higher than desired, loosen the hold down
clamp and turn the distributor slightly to achieve the desired idle RPM.
Recheck the idle mixture needle position then tighten the hold down clamp.
Once the idle system is setup you'll need to correct the distributor's
advance curve. The first step is to attach a timing light and recheck the
initial ignition advance. Let's say, for example, that it was originally 15° and
now it's 22°, a 7° increase. If your total ignition advance was originally 35°,
in order to keep that figure the advance curve will have to be shortened by
7°. Assuming you have a centrifugal advance system you'll have to limit how
far the advance weights can move outward, which will limit the total
advance. The method required will vary from distributor to distributor, so I
won't get into that here, but any competent technician with a good
distributor machine should be able to do it for you.
If you don't have access to said technician/distributor machine and you can
come up with a way to limit the outward motion of the advance weights,
you can do the same thing using your engine as form of distributor machine.
Limit the motion of the weights somewhat, make sure you have the correct
initial ignition advance then check to see how much total ignition advance
you have. If the total ignition advance is still too high, just continue to limit
the motion of the advance weights until you achieve the desired total figure.


AED has some good tips on carb setup, also.

http://www.aedperformance.com/Tuning%20Tips.htm

Amen Brian!!!!!

Sounds like you want my deposition here , what I should have said is that this occurs when the throttle plates are open. Which is why no vacumn exists at the meter block port( except the area below and behind the power valve) until opened and which should not be used on very early cars, but people do because the dont want vacumn to dist until engine revs up or what it may be. All vacumn ports were originallly set at base plates.. It was not until smog years that the ported and unported valves appeared...Today Barry Grant has several port on base plates to help satisfy all needs. Grab a holley handbook and follow the vacumn passages and air bleeds. Gentleman above me did a very good job of explaining the tune up procedure..right out of the book.
Another place that vacumn appears is on the choke body where some Fords have the heat air transfer tube into the exhaust manifold,, little compression fitting screened hole. I rest corrected.

[ 02-12-2005, 07:22 PM: Message edited by: zdld17 ]

A drag race car doesn't need vacuam advance, because it spends zero time at part throttle.

Whole different story on the street tho. At low load, part throttle, the engine is lazy, VE is very low, even at 80 on the freeway, it's only making about 40 HP. It needs more advance for those conditions. lots more.

When we ask it for power, it gets meaner. VE goes up, the flame move faster, and the vacuam can pulls that extra advance out cause the motor don't need it.

As was said, ported vacuam advance came about in the smog years. No vacuam at idle made less polution. As soon as the throttle moved, depended on exactly where the port is, it uncovered the port and the can see's the vacuam.

Using manifold vacuam on the advance can works well for most high performance street motors, mostly because if you set in enuf initial to make the motor happy, you'd hafta use a starter off a peterbuilt to crank it over.

thanks Eric, thanks Greg.

my CSI starter works fine with 39 degrees of timing and 9.8:1 compression

14-18 degrees initial shouldnt be a problem for anything but a real worn out starter.

Thanks for input concerning Holley vac and timing issues... These cases vary from owner to owner and car and driving...
On timing isssue, I use 15 initial and limit dist for a total of 35 -36.. , get 20 mpg with use of TKO. I use no vacumn controls.
As for carb,, I have used 650, 750 & 850 Holley and Demon.. Barry Grant recommended 650 Street Demon with idle eze.. Its ok, but I feel motor runs out of breath,, I keep going back to 750 , feels better as motor pulls much better.. I have yet to try the 850 Demon on with this combination. The 650 seems to make a more desirable low end torque band and when comparing with larger carbs you should understand why. You are not over flowing motors, Bench racers will swear that 750 and 850 are best , even for top end. Using volmetric numbers,, it tells motor is basically an air pump and it can pump just so much air. But we know better, right?

this will help you.
its from holley on how to diagnose and rebuild your carb.
http://holley.com/HiOctn/TechServ/TechInfo/Instruct.html