low engine vacuum at idle help

[sassy383]

i finally got my backfire fixed on tip in. up replaced fuel pump with high flow and adjusted floats. also put bigger metering rods in carb.
i am now having a problem with loading up at idle. i have 68 383 with performer rpm heads, intake, and cam. i have 7 in vacuum at idle but
when i put it in gear it drops to 2-3 in. the low vacuum is not pulling the step up spring down to seal off the primary port when in gear.
is this normal or do i have a base engine problem causing low vacuum. i have the smallest step up spring in that is available, it is a 3in
spring. i can hear and feel the metering rod jumping inside carb.
thanks
pat

[moparteacher]

The metering system (jets,rods,, float level) should have nothing to do with fuel mix at idle. The idle screws should be the only source of fuel mix at idle. If the metering rod position is affecting idle mix then the throttle setting is open too far. Your pulling fuel from the wrong circuit in the carburetor. You need to close the throttle some. If the engine won't run with a lesser throttle position then your problem lies elsewhere than the carb.

Check for a vacuum leak and confirm base timing.

BTW. 2-3 Hg's at idle is too low. It takes a really REALLY big cam to produce that at idle.

Good luck

[sassy383]

i have checked timing and it is about 14 degrees base, the cam is performer rpm so it is not that big. i checked and can find no vacuum leaks at all. the motor is a fresh build and all seems ok. i just cant seem to find why the vacuum is so low at idle. i think this is causing my poor idle and stall.
thanks for help
pat
ps: i am really thinking about the speed demon carb, this edelbrock seems like junk, nothing but problems since the beginning, any goods or bads about these carbs.

[69 GTS Clonvertible]

Do you have a power brake booster?
Hows the brake peddle? spungy?
The guy I purchased my Dart from said he had a problem with the vacuum at the carb when he stepped on the brake to put it in gear. apparently the power brake booster diaphragm was worn out and was making the Dart run like crap but only when he stepped on the brake.
food for thought.

[jess13]

There is nothing wrong with a Eddy carb,  you need to find what the problem is & everything will start falling into place.


Now a couple of thing to think about.  The vacume readings,   are stready and reading low,   or is it real jumpy and reading low?


Vacume leaks can be there & hard to find.   One,   they can leak at the bottom edge of the intake runner if you havant checked there  ( where the intake meats the valley pan).   Also it can leak to the inside of the valley pan where you cant check.    Had this happen,  and it will drive you crazy.  A new intake gasket fixed it for us.


Block off all vacume lines ( including the vacume brake line if it has it)  to check vac & look for leaks.   This way you have no way of anything else effecting you  ( Like a leaky brake booster as meantioned above).


It is possible that the cam is installed wrong and causing the problem.
It is possible that the rocker arms are to tight & causing the problem
It could even be a Valve or valves that are not seating.
Are you 100% sure your timing mark is correct ( pionting at zero when piston is at TDC).


The vacume reading being steady or jumping around will tell us a lot in what to look for !


Jess

[oldkimmer]

Sounds as if ur pushrods r too long.........chech ur preload.......kim..........

[Pro Street dart]

moparteacher & Jess,

While you are here:

I dont what to highjack this thread, But I am getting a minor off-idle stumble on my Eddy 1407, 750 CFM. I totally took this carb apart and went through everything. I believe it still has the OE stuff in it. Reset floats. Vacuum is 10 at idle. I made a mistake and put the pump connector rod in in the middle hole. When it was in the top hole it did the same thing.

Note: I found black junk in the fuel bowls. The fuel supply was filtered through a 10 micron Fram. Could the aluminum at the the bottom of the bowls be corroding? They were stained.

I am not running vacuum advance. I hooked it up once, and the engine dieseled bad when I shut it down.

440,  MP 484 cam.

[Pro Street dart]

fuel bowls:

[moparteacher]

There is a transition slot right above the idle mixture screw hole in the primary bores. This transition slot, in combination with the accelerator pump, is responsible for fuel feed off idle. Proper fuel flow through the transition slot is dependant upon a couple of things:
1. float level. The float level will determine the air/fuel mix in the emulsion tubes. The emulsion tubes mix air and fuel for rapid fuel flow. Too high of a float level will cause a slow fuel signal response and a stumble. Too low of a float level and a lean mix can result along with a stumble.
2. On top of the emulsion tubes are the air bleed holes. Make sure they are not clogged.
3. Accelerator pump level at closed throttle. This is measured at the top of the carb. I don't recall the correct setting.

You can put the accel rod in any of the three holes as long as you readjust the height of the pump at idle.

I think thats about it.

[Pro Street dart]

Thanks moparteacher. I will set the accelerator pump plunger to .594 (from top of pump shaft to bowl top).
What are the 3 holes for
that the accel rod goes into? In other words, would one notice a difference if it were in the bottom hole as opposed to the top?

Would hooking up the vacuum advance help the off idle stumble?

[sassy383]

my engine vacuum at idle jumps from 7-8 in park and 3-4 when put into gear. i have blocked off brake booster,pcv, and
vacuum advance to eliminate that. i have sprayed throttle body spray all around the carb base plate and all around the
intake around the cylinder heads. i have brand new edelbrock performer rpm heads so i do not think i have a valve sealing problem. i have brand new crane rocker arms with correct pushrods with my rocker preload adjusted just like the
instuctions stay (i even readjusted the rockers after engine break in). is there any way this low vacuum may be normal.
everything seems to be ok with base engine.

[oldkimmer]

Back off ur rockers to zero lash and see if it helps, ...........kim.............

[farmington]

Was the cam degreed in or just lined up the dots.  Cam might be retarded.

[jess13]

I agree with trying the Zero lash.   What intake are you running?      Edelbrocks out of the box new have been known for there vavles to leak a little.  That is why everybody always have a new valve job done on them when they are bought new.    The vacume should be real steady,  but if a valve leaks bad it will jump around alot some times.  If your RPM's is not real stead that could acount for a little vacume movement,  so you may be alright on that.

But I would try backing off the lifter preload and see how it effect it.  With to much preload it will try to hold the valves off the seat just a little which could be enough to cause what is going on.  Really with your cam combo you should have more vacume than you do.  So I dont fell it is normal for you setup to just have the 7in of vac.   It should have enough to hold the meatering rods down with the lightest spring, that is for sure.   The cam needing to be degree in could also be something.


After trying the lash backed off, if it doesnt help,  try to just turn some extra timing in & see if the vac starts to pic up.


Jess

[sassy383]

i will try 0 lash on my lifters, i set them to 1/2 to 1 turn just like the instructions. the idle does seem a little bouncy which could be the jump in vacuum. the idle really jumps up and down in gear. the cam, intake,heads, and timing chain are all
edelbrock performer rpm, rockers and pushrods are crane. i did not degree the cam but i lined the marks straight up on the timing chain when i put it in. i could have gone 4 degrees retard or 4 advanced but i did like the instructions said and put it straight up.
thanks for all you guys help, yall are great
pat

[speedymopars]

Have another person ready to help. I personally don't think it is anything anyone has said.

Let it idle, and drop it in gear. Manually move the rods down so the enrichment isn't kicking in. What is your vac reading? If you put it into gear, and the enrichment kicks in, then you are running way too rich and the vac readings will go down. See what manually moving the rods do.

How many RPM does it drop when you put it into gear? If it drops more than 300 RPM, its too lean.

Try to increase the idle speed. What are you trying to get it to idle at?

How much duration is on the cam?

[sassy383]

the idle is set at about 1,000 in park, it drops to about 500 when in gear. i can hold the metering rods down manually and it seems to idle much better. i think the problem is there is just not enough vacuum to hold them down in gear. i will have to check the exact vacuum when manually holding the metering rods down tomorrow. i have moved the idle mixture screws out 4-5turns and they do not seem to be effecting the idle, i have also turned them in til the stop and it still does not seem to effect the idle much at all. the ims seems almost like it does not work moving it in or out. the cam
is 238int and 246 ext duration at .050 and lift is 480 int and 495 exh
pat

[jess13]

If its not effecting the idle when you turn the idle screws in then it is way off on the mix.  Have you tried holding the rods down & ajusting idle screws, with the rods bouncing they probably want effect it much.  It is very possible for the fuel mix to kill your vac if its off that far.   But I would still give the zero lash a shot,  I have seen it to many times cause problems.   It will be very noticable if it is causing the problem,  the idle will jump way up after backing the lash off.   If you cant find no joy after trying these things,  maybe someone would let you try a carb ( buddy or friend)  just to see its effect.



I have never ran that cam,  but I really dont see it being that low on vac because of it.  What ever the problem is,   dont let it get you down, when you hit the fix your car will change instantly & you will like that carb.   Well, unless its the carb that has the problem, sometimes there can be crazy stuff wrong inside of them (any carb for that matter).  Bad castings, passage ways stoped up & cant be opened  ,ect,ect.


Jess

[gt]

p-womac1.
i don't think it is your cam. I have the MP 557 lift cam and I am getting 11-12" of vacuum at idle.

good luck

gt

[sassy383]

ALL YOU GUYS ARE GREAT, I WILL TRY THE ZERO LASH TONIGHT AND GIVE THAT A SHOT
THANKS A BUNCH
PAT

[sassy383]

ok, i adjusted my rocker arms to 0 lash, it still idles the same and still has the same vacuum. the only difference now is i have a little lifter noise. i guess i will call edelbrock and see what they have to say. thanks for all the help.
pat

[Prodart]

Scary question have you checked the rocker arms for equal lift? A wiped cam will give the problems your experinceing

 Or a vaccum leak

[moparteacher]

Somethings just not righht here. First there are only a few things that will cause low manifold vacuum, and at a thousand rpm it's gotta be serious.
#1 Engine mechanical problem This may include bent or burnt valves, serious vacuum leak, incorrect cam timing, badly scored or worn cylinder walls and bad rings

#2 Incorrect ignition timing or wrong firing order.

1st. Double check the firing order. 2nd Don't assume the timing mark on the balancer is correct. Take the bolt out and look at the alignment pin on the snout of the crank. Is it lined up with the tdc mark on the outer ring?

2nd Why is it idlling at 1000 rpm? When you fix the vacuum problem lower the idle.

3rd. And this is very important. You will never be able to set idle mixture if the primary throttle blades are open too far. When the throttle blades are open too far the manifold vacuum draws fuel  from the main circuit (out the venturi). This is why when you close the idle mixture screw it still runs. That's your clue the throttle is open too far at idle. It's supposed to die when the idle mix screws are turned in. This is because the the idle circuit is the ONLY place fuel should be drawn from during idle (choke off).

Moving the metering rods up/down in/out should have absolutely no affect on idle speed or mixture because thats not the idle circiut, it's the main circuit and power enrichment circuit. The only effect, if any, would be a small vacuum leak if you were to remove the metering rod pistons completely while it's idling.

Here's how you check if the primary throttle blades are open too far:
Looking at the front of the carb there are two small vacuum ports on the front of that carb. One sets low near the base and the other sits a little higher on the other side. The one low near the base is manifold vacuum. The one a little higher on the other side is venturi vacuum.

When at idle there should be no vacuum signal at the port that is raised a little higher, the venturi port. If there is any kind of vacuum signal on the venturi port during idle then the primary throttle blade is open too far and you are drawing fuel out from the main circuit and it will be nearly impossible to tune correctly.

Also check the back/center of the carb and make sure you have a 3/8 pipe plug in that port. Do not run the PCV off the the back port or any other port except the one that is front and center in-between the idle mix screws.

Let me know what you find.

[sassy383]

ok i did check the vacuum on both ports on the carb, i have vacuum on both of them at idle. i have the idle set to
1000 rpm in park to prevent dying when i put it into gear. i suppose i could have a base engine problem, but the
engine is a fresh over haul, bored 30 over with all brand new parts, pistons, rings etc. i checked absolutely all clearances
to the T.  it has brand new everything, cam, timing chain, pistons, performer rpm heads, etc. the engine has maybe 100
miles on it. i have checked and double checked timing, it is set at 16 degrees. it does not have problem starting or
problem dieseling when turning off. the firing order is good. the engine runs very very strong from 2500-5500 rpms i just
have a problem with the idle. i have put the 3.8 plug in the back of the carb and my pcv is running off the frt center
of carb. i have checked for vacuum leaks to the best i can. i plugged off all ports pcv, brake booster, etc. sprayed throttle cleaner all around the carb and intake and has absolutely no effect.
thanks for all the help and let me know what you think
pat

[sassy383]

i also wanted to let you know that i turned both idle mixture screws all the way in at the same time at idle and the engine does die. previously i was just moving one at a time all the way in. sorry for not being more clear
thanks
pat

[blown71duster]

A good way to make sure all the cylinders are firing ok is to start up the engine cold for a few seconds , then shut off and feel the header tubes to make sure they are all even. Its a quick way to pinpoint if there is a bad cylinder with vacuum leak or a mechanical problem.

[69 GTS Clonvertible]

Pat,
What's between your valley pan and heads? how can you test to see if you do or do not have a vacuum leak here, without removing the intake and pan? especially if it is on the internal area of the pan, pushrod/cam area. I was having a problem with my idle speed jumping up and down because I had a vacuum leak in this area, my tach would fluctuate from 800 rpm to 1200 because of this, I sprayed starter fluid around my intake and carb base waiting for the idle to jump up, with no luck, so I thought it couldn't have a leak here. I don't have an auto-trans so when I put mine in gear it is esentially in nuetral, untill I let the clutch out, and give it some gas at the same time. I pulled the intake and valley pan off and added the gasket material between the pan and the heads and between the pan and intake and I haven't had a problem since.
Before I put the gaskets in, I had been told to just use a thin coat of gasket sealer around the intake ports on both sides of the valley pan, and no gaskets, so that's what I did and after a few weeks of running it the sealer must have been sucked into the intake port, or it may have been blown out or burnt because of a backfire through the carb. I recall you had a backfire problem. maybe the problem is like I explained.
Shawn

[sassy383]

i will check the headers after starting cold and see if it shows any signs. as far as the intake. i have a gasket on both sides of the valley pan, between the pan and head and between the pan and intake.
pat

[69 GTS Clonvertible]

So what did you find out?

[farmington]

What are you running for a torque convertor.  Sure seems like a lot of drop in idle speed in gear.  Mine doesn't drop more than 100 rpm when I put it in gear.  I have a 284-.484 MP cam, which is a little smaller than what you have.  It idles at 750 rpm in gear with the brakes on and around 8" of vacuum.