Joel Adams
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

yes, float levels are at the bottom edge of the site plug and everything is sealed well.

I may try out my demon 625vs...

Whats the history of the carb?  Where did you get it?  How old?

I would not drill anything or put wire in any holes.

What cam is in the engine?

After Shark - It is a brand new carb (4777) from Summit (new but sat for a while before install)

The cam is not stock but mild, unsure of specs. I plan to install the new lunati voodoo 262/268 cam in a few weeks.

I was told all holley dp's run too rich at idle and the only thing to do is modify with holes/wires and that it was recommended by Holley - I did not see this anywhere on their web though!

I know you work for Holley so I would love to hear more from you on this. Do I just need more cam?

Here are my current engine specs:

Vortec heads with Z28 springs (~9.7cr), vortec performer intake, full roller rockers, hei recurved 36 degrees at 2,800 52 degrees total, 1 5/8" hookers, 2 1/2" dual chambered with h pipe, 2,000 stall (th350), 3.70 posi

This is what I was told at another forum

http://forums.corvetteforum.com/showthread.php?t=1002801

Thanks After Shark!!

First things first and for anyone reading this, never adjust anything on a carburetor until you first take it out of the box, bolt it on and take it for a test spin.  Also no where in any offiicial Holley literature will you find information about running wires down into circuts.  However we will recommend drilling throttle blades on high lift big duration cams where very little manifold vacuum is created.

What may work good on one engine and one combination most of the time will never on someone elses combination.

So first I would return the carb to its ouf of the box state.  That means resetting all those adjustments that Lars said to do.

Now you said the carb has been setting.  How long?  A carburetor that sets too long can cause the gaskets to dry out and shrink.  Plus todays fuels have all sorts of additives that can cause gaskets to not last as long as they did in the old days.  While everything on the outside may appear ok, interally you can have vacuum fuel leaks between the circuits on the metering blocks.  This can cause bad idle, rich conditions, poor acceleration, all sorts of things. 

If its only been setting a few months your probably ok, 6 months to a year.  You might want to just change out the fuel bowl and metering block gaskets.  If you do make sure you get the right ones for the carb.

Once you have the carb back to its factory settings bolt it on and hook everything up correctly.  Power brakes hook to the base plate on the under side of the carb, distributor vacuum connects to the primary metering block.  Other vacuum accessories can connect to the other vacuum ports.  Screw each idle mixture screw in until it lightly seats and then back each one out 1 1/2 turns each.

Start the engine.  let it fully warm up.  You might need to turn the curb idle screw so it will idle on its own at the correct RPM.

Set the idle mixture:

A double pumper draws idle fuel through the tiny holes just below the throttle plates.  The screws on the metering blocks control the amount of fuel to these holes.  The fuel is also pre emulsified though the air bleeds on top of the carb.  On a double pumper screwing the needles in leans the mixture.  All the way in will shut the idle fuel off.    To set the idle mixture you should use a vacuum gauge or you can use a tach, although it may not be as accurate.  You will be tuning for maximum RPM or maximum Vacuum.  In reality your trying to fine the leanest mixture the engine will run on at idle.  With the engine warmed up turn in each screw an equal amount.  I would start small with an 1/8 of a turn.  You should start to see a rise in engine rpm and/or vacuum.  Continue until you find the highest RPM or vacuum reading.  Once you go to far in then engine rpm will start to go back down.  Back the screws out just until this point where the engine rpm or vacuum started to fall off.

Nope your still not done at this point.  Now if you look your engine is most likely idling anywhere from 50 to 250 rpms more then it should.  So go back to the curb idle screw and reset the main idle. 

Nope still not done.  Now go back and follow the same procedure on the idle mixture screws until.  Again highest engine RPM or Highest Vacuum.  Keep going back and forth until there no adjustment is required between idle mixture or curb idle.  This is your lean best mixuture.

Things to note:  If you turn the idle mixture screws and there is no effect to idle then you might have a blown power valve.  An easy way to tell is to simply continue to screw the idle mixture screws in while the engine is running.  If you seat both needles and the engine continues to run then that means fuel is gettting into the engine from somewhere.  Most likely the powervalve.  However if it does continue to run you can shut the engine off and remove the carb.  If you fip it over look at the postion of the throttle blades.  If they are up on the transition slots then you are starting to pull fuel from the main wells.  You will need to correct the throttle postions before you can move forward with any tuning.

After the idle mixture is set.  Take it for a drive.  Notice anything that you don't like.  Perfect, hesitation or bog are what most people find at this point.

Bogs:  Are typically created by too much fuel entering into the carb.  What this means is the air fuel mixture is too rich.  Too much fuel to too little air.  So we have to take some fuel out of the mix.  The easiest way is to go down on the squirter size.  The squirters are the tower looking things down in the carb.  if you open the choke horn and move the throttle you will see them squirt fuel into the carb venturii.  Going to a smaller sized squirter means less fuel will be metered into the carb.  However this does not change the ammount? Those pump diagrams on the front and rear of the carb hold 30cc of fuel each.  If you mash the throttle those pumps will eventually meter all 30ccs into the carb.  The squirter changes the discharge rate and amount causing it to spray less fuel over a longer period of time.  What happens during this bog is your getting so much fuel at once its overloading the amount of air making it to rich for the engine to turn it into power.  You can also adjust this by changing pump cams on the linkage, but in most cases this will never be required.

Hesitate:  Opposite of bog.  This is where the engine might pop, backfire, fall over on its face and then take off like a bat out of .  This means the engine got lots of air, but no fuel to make power out of it, until the primary jets kicked in.  Here you just need to go up in squirter size to correct.

Squirters:  All Holley carbs have squirters.  Basically there is a time lag period between the idle circuits and the main jets and the squirter is designed to provide fuel to the engine during those periods of acceleration and periods where the throttles are rapidly opened. 

Make one change to the squirter size dropping one side at a time starting with the primary side.  Test driving each time you make a drop until either one of those situations above is resolved.

Main jets:  Everyone thinks they can call into our company give their combination and we can tell them the jet size.  Impossible.  The only way you can do this is with driving.  I can tell you from experience that carbs are typically too rich out of the box.  Mainly to protect you and your engine.  If we shipped them lean there might be some torqued off people that hurt their engines before they realized they were lean.  Here you can use track speed, chassis dynos, and plug readings to determine jet size.  Obviously if you start taking jet sizes out and power goes up you were on the rich side.  Again if you go too far you've gone too lean and power will fall off.  If you go up in jet size and power goes up means you were lean.

I would only move one jet size at a time downward to see how throttle response and plug color reads.  Usually throttle response willl go up if you are headed in the right direction.

If nothing works then your gaskets may just need to be changed.  I hope some of this info helps.

Great information from a reliable source!

Now I wish I knew what the out of box settings were... I have looked on Holley's web but couldn't find them.

What I changed is: set primary throttle plates to .020 (square hole) and matched the "light gap" for the secondaries since the inlet is higher up and would be open too much.  ---what is correct for this?

Then only other changes I made were to make sure the pump shot was immediate at the correct throttle position.

Is there a recommended idle advance for a 4777 - I have 12 initial? I also ran my hei on manifold vacuum gm part#vc1862 2-4hg 8 degrees advance. Could this be part of the idle trouble?

Like I said, the carb is much more powerful than my qjet while accelarating and WOT, just very rich and dies while on the idle circuit. The carb only sat a few months and had not been used previously or had gas in it.

I did go back and forth between the idle mixture screws and curb idle screw but it either ran rich or wouldn't run at all when I hit that point - using 1/8 turn increments. I ended up with 1 3/4 mixture out.

Thanks After Shark - I really appreciate your time on this.

Is there a recommended idle advance for a 4777 - I have 12 initial? I also ran my hei on manifold vacuum gm part#vc1862 2-4hg 8 degrees advance. Could this be part of the idle trouble?

[/QUOTE]

this is definitely wrong..  this should be connected to metered or timed vaccum on the carb..

http://www.vetteprojects.com/bmv

this is definitely wrong..  this should be connected to metered or timed vaccum on the carb..

I agree with Ben.  I went back and looked at your first post and I think you have some other issues going on.

First timing.

52 degrees total.  Thats not possible unless you like picking up spark from the wrong cylinder.  You should be aiming for 36 degrees total and 10 to 12 degrees at idle. 

Verify that your rotor is pointing at the number one cylinder at TDC on the compression stroke.  All you need to do is make a mark on the distributor body where the number one post is located.  Pop the cap off and it should be pointing at it.  If not you may be off a tooth or our 180 degrees.  Don't feel bad, I've made the same mistake.  Just fix it.  What I do is drop the distributor in with the rotor pointing at the mark on the body.  Then I rotate the distribtor body counter clockwise so the leading edge on the number one post is lined up with the leading edge of the rotor.  This will allow you some advance for setting the engine, but you need to set it correctly with a timing light.  There should be no change to the initial timing when you plug the vacuum line from the distributor vacuum advance into the metering vacuum port on the carb.  To verify everything is working you will able to advance the throttle to 2200 to 2800 RPMs and see the total timing.  Aim for somewhere between 32 to 36 degrees.

You also might have a manifold vacuum leak causing the idling issues.  You stated a new intake and its not uncommon end up with a vacuum leak in the valley if you were not generous with the sealer in this area. 

With the cam you have you should have a vacuum reading of no less then 8 inches.  probably closer to 10 or 12.  If i rmember correctly even our new Voodoo cam makes 10 to 12 inches depending on the engine setup.

If the vacuum fluctuates all over the place then you most likely have a leak.  One thing for sure if your timing is not correct or you have a vacuum leak you will never be able to get your engine to idle and you will never be able to tune the carb to the engine.

Now you have the problem of getting the carb back to out of the box.  IF you take the carb off you will see a tiny hole in each venturii.  Those are your idle feeds where the fuel enters into the intake with the throttle blades at idle.  A little further up the venturii you will see slots.  Those are the idle to main well transfer slots.  The more you open the throttle blades are opened the less vacuum signal the idle circuit receives and is transfered over to the main circuits engaging the fuel through the main jets.

If you throttle blades are open where they are up on these slots you need to back them down.  In fact I would back them down to where they are just above those tiny idle holes.  Put the carb back on and start the engine.  You should be able to give the curb idle screw a quarter to half turn and the engine should idle on its own.  If not you may need to open up the secondary thottle blades.  That will require taking the carb off.  there is a tiny screw off to the side recessed into the throttle plate.  use it to open up  the secondary side slightly.  probably a quarter turn to start with.  Put the carb back on and try it again.  This will allow you to back the primary curb idle screw back down allowing more air and fuel to pass through the secondary side.  You have to get the engine to idle before you can do any tuning.  Once you have the engine idling at the correct RPM you can follow some of the tuning procedures I gave in an earlier post.

I really think you have another problem that is making you think it is the carb.  You would be surprised how many times people call into our tech group that have made a lot of changes at once, but will blame everything on the carb.  Mainly because it has all the adjustments, last item to go on, and its on top.  They also never think that just maybe their might be a vacuum leak or they got the distributor in wrong.  I remember one time putting an itake on and because engine compartments can be cramped and dark, I accidentily got a vacuum hose caught between the intake and the block.  Bolted everything together, forgot there was a missing vacuum connection, and when I started the engine it refused to run.  Created a major vacuum leak.  After investigating I wanted to kick myself.  Dumb, but it can happen to anyone.

The key is to make one change at a time and see what affect it has.  Remember baby steps.  Also if you don't own the following tools I would go beg, borrow, or buy them.  I would never recommend changing a cam, carb, intake, distibutor or doing any engine tuning without them.

Vacuum Gauge -

Timing Light - All you need is a basic one, but if you can afford one with a advance dial on it, do so you will be much happier.

Degree Wheel

External Tach - I use a small tach and put alligator clamps on the wire ends for quick connection.  this way you have a tach reading right there with you while tuning.

Sorry if your having trouble.  Trying to diagnose problems over a forum or even a phone can be time consuming and confusing.  I hope this information is helping.  Also Ben and Ken as several others on here are very knowledgeable and can help as well.  Let me or everyone else what other problems you are having and we should be able to get you up and running.  You could always put that speed demon on just to rule out any carb issues, but my guess is your problem won't go away because you have something else going on.

I REALLY appreciate you guys taking so much time trying to help me out!

I'm going to follow After Sharks instructions this week and will let you know how it goes. There is certainly a possibility of a vacuum leak even though I was very careful.

My total timing is 36 @ 2800 but with the vc1862 canister it should be 52.

I know my hei is installed correctly.

I do not have the voodoo cam installed yet since I can't find one on the market yet (I have ordered it from Summit) - have mild cam now

From what you've said I know I need to:

1. change my vacuum advance to ported
2. close my throttle blades because the primaries ARE on the slots and the secondaries are open just as far (but not on the higher up slots)
3. Tune back and forth with vacuum gauge/idle mixture screws vs idle screw

here are some images that will probably help you.

If you look closely you will see the transfer slot is not exposed or the throttle blade is right at the edge.  this is what you want to strive for.

On another note, I have never seen anyone run 52 degrees not even racers.  So IMOO your distributor setup is completely wrong.  Not sure if anyone else will step up and agree with me or not.  I've been doing this a long time and you should strive for 10 to 12 degrees initial with a total of 36.

So keep us posted. As I'm starting to believe you have a vacuum leak. 

this is definitely wrong..  this should be connected to metered or timed vaccum on the carb..

[/QUOTE]

Not necessarily.  Often (usually) manifold vacuum will give you a better (more stable) idle.  Ported vacuum was invented for polution control and is not necessarily conducive to manageable tuning!
 
[/QUOTE]

I hate to disagree with you..  but i must..  first the vacuum advance isnt supposed to help at idle..  manifold vacuum is highest at idle and its going to give you more advance at idle.. 

at higher rpms..  when you want more advance..  your manifold vacuum drops off..

your not even supposed to have it connected when you set your timing..

ive never heard of anyone running 52 deg total advance either..  36-38 is about as far as your go

http://www.vetteprojects.com/bmv

this is definitely wrong..  this should be connected to metered or timed vaccum on the carb..

[/QUOTE]

Not necessarily.  Often (usually) manifold vacuum will give you a better (more stable) idle.  Ported vacuum was invented for polution control and is not necessarily conducive to manageable tuning!
 
[/QUOTE]

I hate to disagree with you..  but i must..  first the vacuum advance isnt supposed to help at idle..  manifold vacuum is highest at idle and its going to give you more advance at idle.. 

at higher rpms..  when you want more advance..  your manifold vacuum drops off..

your not even supposed to have it connected when you set your timing..

ive never heard of anyone running 52 deg total advance either..  36-38 is about as far as your go

 [/QUOTE]

Really?????

http://www.corvettefaq.com/c3/Vacuumexplained.doc

Actually Ben is right, and wrong.  All of his statements are correct.

BUT there are several production cars that do have vacuum applied to the vacuum advance at idle.  They start at base timing, then apply advance right away at idle.  This was done for emission purposes and does nothing to make the car run better.  Cleaner yes, better no.  And it's only cleaner when several other pieces of emissions equipment are in place and functioning.

They do exist.  There were a few years where there were quite a few of them.  They perform poorly, get lousy mileage, but do run cleaner.

Oh Boy.

Lars is partially right in some of his writings.  I'm not going to pick it apart, but you need to hear me on this and I'm not trying to be an A-hole about it.

Yes if you hook up your distributor vacuum to a direct manifold vacuum port at Idle it will pull advance.  So lets say you set initial with the vacuum hose off at 12 degrees.  If you plug it into direct manifold vacuum the vacuum advance will pull more advance probably around 30 to 32 degrees depending on the unit at idle.  But what happens when you crack the throttle to accelerate?  The manifold vacuum goes away.  That causes the timing to drop or basically is  retarding your timing which will cause the engine to fall on its face.

I can tell you if you look in the photo that I posted that shows where to hook up your vacuum advance on a Holley Carb that port will pull little if any vacuum at all at Idle.  Trust me I work for the company and have first hand experience with them.  This is where your vacuum advanced needs to be connected.

Ben is right I would leave the vacuum hose off to set your initial just to be on the safe side, however if you want to connect the hose it won't cause a problem during initial.  Aim for 10 to 12 degrees.  Plug you distributor into this port.  Advance the throttle and you will see your timing advance.  This port is tied to a signal port in the venturi so it will see eddy currents as air passes by it creating vacuum pull on the distributor.

If you don't believe me just put a vacuum gauge on the various ports and operate the throttle and watch what happens at each of the ports as the throttle is opened and closed.

Here is a diagram that shows what happens in a carb veturi during operation.  Its right out of one of our Holley Handbooks.

Thanks After Shark for the pics and additional exp.

I am going to stick with recommended setup from you/Holley.

I'll change back later this week when the weather is better and will let you know what happens.

Actually Ben is right, and wrong.  All of his statements are correct.

BUT there are several production cars that do have vacuum applied to the vacuum advance at idle.  They start at base timing, then apply advance right away at idle.  This was done for emission purposes and does nothing to make the car run better.  Cleaner yes, better no.  And it's only cleaner when several other pieces of emissions equipment are in place and functioning.

They do exist.  There were a few years where there were quite a few of them.  They perform poorly, get lousy mileage, but do run cleaner.

[/QUOTE]

well i will admit ive never seen a car use manifold vacuum..  the very concept is foreign to me.  It makes no sense..  anyone who has installed a high duration cam in their corvette and had there vacuum accessories die knows that manifold vaccum is unreliable.  There is plenty of information of the internet that can be usefull and plenty that can be less than usefull.    

I agree with AS's suggestion on this..  hook up a vacuum gauge to your manifold vaccum..  then play with your throttle.  the vacuum gauge does not lie.  then try to make sense of that article. 

just think of throttle plates when open as huge vacuum leaks.  much like a vaccum cleaner..  when you take the hose and hold it against your hand it sucks real hard.. when you take your hand off and allow air in the hose the suction is much lower.. 

its very simple.. ported vacuum increases with throttle, manifold decreases.  I can think of no exceptions to this rule.  so to hook up vac advance to manifold vacuum gives you all of your advance early and none of it late. 

remember the article on the internet that warned of people putting aids infected needles in phone booths, KFC changed their name because they are no longer using chicken, etc etc.  just because someone wrote it doesnt make it true.

I take back the part about not having ever seen it..  ken.. do you know if a 1978 plymouth volare station wagon (slant 6) had this setup..  I remember seeing some craziness like this and just assumed some idiot had messed it all up..  i reconnected it "properly" and the car ran much better..  i wound up having to detune it some because it kept on doing one wheel wonders...

http://www.vetteprojects.com/bmv

Thanks AS, cthulhu and everyone.

The explanation really makes sense about vacuum sources!!!

AfterShark, those drawing look almost exactly like some I have used in class.

Ben, I'm not sure the slant 6 ever used the manifold to dist setup.  Even the cars the did use it ran better if you switched it to a ported vacuum.  You also had to reset timing. As i said, it helped emissions, and everything else suffered.  Several Olds cars had this, and some other GMs.

One more point.  Ported vacuum also goes away at Wide Open Throttle.  There is no vacuum until the throttle is opened, then it builds, and at WOT it goes away.  This is actually a benefit.  As we go to WOT the carb becomes richer than at idle or mid throttle.  This pollutes, but creates more power.  Due to the richer fuel mix, the flame in the cylinder travels faster than the previous leaner mix.  This means a drop in vacuum and a bit of timing retard is in order.  The later timing compared to the faster burn creates the peak burn at the same time as mid throttle more advanced slower burning leaner mixtures.  You still have mechanical advance from the distributor weights, so timing does not go back to base.  Computer cars are programmed to operate in a similar fashion.

Some times a venturi vacuum is used.  It is a much weaker signal, but very accurate.  It does not exist at idle and peaks at WOT.  Due to the weak signal it needs a vacuum amplifier to operate anything, and modifies manifold vacuum to control a given device.  That means at WOT the manifold vacuum still goes away, but the control is better.

Bottom line, use Bens and AfterSharks recommendations if you want it to run the best.

I'm sorry but have not had time to start her up yet. I have a 2 month old that became sick - BUT, hopefully this weekend!

Thanks again for your help.

Great News - The vette is running very smooth thanks to AfterShark and everyone elses help.

Here's what I ended up with:

1. Changed vacuum advance from manifold to timed port
2. Had to increase initial timing to 16 BTDC
3. Idle mixtures screws are at 1 1/8 each
4. Primary idle transfer slot - blades are just on it so any movement will expose. ( i did have too much exposure) After I got it running well I took the carb back off to see this.
5. secondary idle transfer slot was closed some (gap matches primary side)
6. Idle in Park is 1300
7. Idle in Drive is 700
8. Runs very smooth with quick response - much better than the qjet.

Thanks again. Now I can work on installing my new Lunati Voodoo 262/268 cam!

Great News - The vette is running very smooth thanks to AfterShark and everyone elses help.

Here's what I ended up with:

1. Changed vacuum advance from manifold to timed port
2. Had to increase initial timing to 16 BTDC
3. Idle mixtures screws are at 1 1/8 each
4. Primary idle transfer slot - blades are just on it so any movement will expose. ( i did have too much exposure) After I got it running well I took the carb back off to see this.
5. secondary idle transfer slot was closed some (gap matches primary side)
6. Idle in Park is 1300
7. Idle in Drive is 700
8. Runs very smooth with quick response - much better than the qjet.

Thanks again. Now I can work on installing my new Lunati Voodoo 262/268 cam!

[/QUOTE]

hey when you get that cam and want to setup your idle to give the best off the line response..

I like tuning with a vacuum gauge on intake vac..  in fact im installing a holley inline vac gauge on the manifold to help with tuning (also a shut-off valve on the vac feed port to isolate the vac systems during tuning)

ive gone over this a few times in detail in other threads..  but to summarize..  adjust your idle mix and timing to the point where you get peak manifold vacuum.. 

there is no hard and fast rule to what the "correct" settings are..  variations in every engine make it difficult to come up with a set of setting that "always" take you to the peak of performance.

if you adjust your carb and timing to peak manifold vaccum at idle..  this gets you to the point where the engine is "hungriest" for more air and fuel. that way when you give it some throttle your "satisfying" it..

a good vaccum gauge is one of the most important tools the performance oriented mechanic can have.

http://www.vetteprojects.com/bmv

Bens right.  If your on this forum and have a carburetor on your engine, you should have a vacuum gauge in your tool box.  Their not expensive and are a useful tool.