Vacum readings?

[porkchop]

I am trying (as usual) to get my carb tuned correctly. I have hooked up the vacum reader and it will not stay steady at idle. Is this normal? I can get it close by adjusting the idle screws. I have to have them turned out about 5 turns so that it will only flux about 5 psi. As soon as I hit the gas it will be rock steady. Could this be caused by an air leak somewhere? Or what about exhaust leaks? I am so tired of playing with the carb. I have not been able to go onto other things because I am still playing with the carb. HELP!

Oh yeah this is the Edelbrock 1405. I have installed the off-road kit. It is on an Edelbrock 2131 intake, and I have done the TFI upgrade. Thanks.

[ August 12, 2001: Message edited by: porkchop ]

[OBX-AUTOMOTIVE]

PORKCHOP...FIRST I CAN'T HELP YOU....I'M NOT TRYING TO BE A SMART Great Googley MoogleyGreat Googley MoogleyGreat Googley Moogley,,,BUT WHAT THE HELL GIVES...WITH ALL OF THE CARB TROUBLE EVERYONE HAS...FIRST I'M NOT SAYING I CAN FIX ANY OF THEM .....BUT IT'S BEEN YEARS...WELL! I JUST REBUILT ONE FOR A FRIEND A 2V HOLLEY ON A 65 F 100...I DID A LITTLE ADJ AND GO>>> THAT WAS ABOUT 6 MOs AGO...SAW HIM THE OTHER DAY,HE NEVER SAID ANYTHING ABOUT IT, SO I GUESS IT'S STILL OK!! THAT WAS THE FIRST ONE THAT I REBUILT IN YEARS...HELL.... I'VE RUN TWO FOURS,TRIPS,Q JETS,AFBS, AND I DON'T REMEMBER HAVING A LOT OF TROUBLE WITH THEM..... WISH I COULD HELP WITH THE VAC :confused: BUT I DON'T REMEMBER HOW!!SORRY!! JUST ME THINKING OUT LOUD ON THE CARB TROUBLES.... ...GARY smile.gif smile.gif

[64Trvlr]

PC
How many inches of vacume do you have on the vacume gauge? By 5 turns out do you mean from all the way in and seated? What do you have the vacume gauge hooked to to have 5 PSI? First things first, is the timing set? Do you have any vacume leaks? Are the spark plugs good? If all that is good what is the idle speed? I'll check back for the answers in a bit and see if I can help you out.
:cool:

[Bob Barry]

Well, that's not normal. The gauge should not move more than within a 1" range. Sounds like a bad vacuum leak is preventing you from getting a smooth idle (five turns out sounds like a lot, but I've never worked with an AFB design).

[Stauter]

Porkchop here is a site that can shed some light on your bouncing vac readings.
http://www.centuryperformance.com/vacuum.htm

HTH
Craig

[64Trvlr]

Good site, thanks.
:cool:

[<RUDYC>]

Where did you plug in the vacuum guage too?
What is your timing set at?
What is your vacuum reading?
What did you set your floats at when you put in the off road needles. I turned out mine 4 1/4 turns out so it aint too bad I guess. I got mine ptetty steady 18-19 hgs http://home.earthlink.net/~zzjoecool/_uimages/318AFB.jpg

[porkchop]

WOW! Stauter, Thanks, that is a great site. I will go out and play with the info fom it tomorrow.

64Trvlr, I have about 15-18 inches of vacum (it bounces really bad but this seems like where it is). The idle mixture screws turned out 5 turns. I have the gauge hooked to the intake were the brake booster vacum hooks up. I think this might be ported because as soon as I hit the gas it goes up to about 25-30. I may have to find another source and then try again.

Bob, it is definately not normal! I need to get rid of this problem so I can start on the rear seal and the T-case swap (whenever I get the adapter, do you know anyone that has one :D).

[porkchop]

Sorry RudyC, I was typing as you were posting. My timing is set to 10 before, and I set my bowl to 7/16 with a drop of 1". This is what the manual said.

[<RUDYC>]

PC you may want to find another place to get your vacuum reading as the brake booster may be affecting your reading. I use a fitting on the threaded hole on the back of the carb.
18 hgs is a good reading. But it may be something else as it is a high milage motor. Valves, seals rings and all that.

[Slippery]

<BLOCKQUOTE>quote:</font><HR>Originally posted by &lt;RUDYC&gt;:
Where did you plug in the vacuum guage too?
What is your timing set at?
What is your vacuum reading?
What did you set your floats at when you put in the off road needles. I turned out mine 4 1/4 turns out so it aint too bad I guess. I got mine ptetty steady 18-19 hgs http://home.earthlink.net/~zzjoecool/_uimages/318AFB.jpg <HR></BLOCKQUOTE>

Oh, no! He's got Ralph's Disease--attaching a random photo to every post!

Just kidding :D

[nograin]

Worse than that, he's got "new member" disease. What happened Rudy? Did you swich computers or servers or something? Besides - I miss the quote from The Road Warrior :D

The only source for ported vacuum is going to be off of the carb itself. The instructions that came with it should tell you where. If you don't have EGR, than just cap it off. Usually one or two small ports.

Like Rudy said, if you are hooked to the Brake vacuum by Tee then that could do some odd things. Usually the brake line is pretty darn big. Any smaller port off of an intake runner will do, or one near the base of the carb. Don't use the PCV line because that too is large, and will have its own weird fluctuations to some degree.

One last thought, How is the vacuum actuated timing advance hooked up? On a 1967 that goes right to the manifold vacuum - no CTOs and ported stuff. That makes a huge difference on your timing at idle. Also a good location to T in. (Yes set basic timing with the vac advance plugged, then hook the advance back up)

Hope this was helpful, not more confusing :confused:

EDIT here:
Also just thought that if you have a poor connection on one of your spark plug wires...just might want to make sure they are all snapped in good. A misfire would show as a fluctuation too, although I suspect you would notice this cause as a problem on the road as well.

[ August 13, 2001: Message edited by: nograin ]

[porkchop]

<BLOCKQUOTE>quote:</font><HR>Originally posted by nograin:

One last thought, How is the vacuum actuated timing advance hooked up? On a 1967 that goes right to the manifold vacuum - no CTOs and ported stuff.

<HR></BLOCKQUOTE>

I am running a '79 360. I don't have anysmog on it at all though. I am going to try to run it from a different spot this evening and see what happens.
Thanks.

[Lindel]

PC, the first thing I would look at is the idle screws being out 5 turns! Mine are only out 1 full revolution with my 1406, on the Edelbrock 2131. I take my readings off the vacuum port just behind the carb, where the vacuum resevior gets it's source from. I'm getting a solid 20", with a minor fluctuation when it gets to cylinder no. 2 (drops 1" of vacuum, for that split second), bad valve, but the engine is blowing oil badly, and needs a new engine to fix.

It sounds as if you're running extremely rich to me. Try bringing in the idle mix to about 1.5 turns, and see what the vacuum does then.

[ClarkGriswald]

<BLOCKQUOTE>quote:</font><HR>Originally posted by nograin:
On a 1967 that goes right to the manifold vacuum - no CTOs and ported stuff. That makes a huge difference on your timing at idle. ]<HR></BLOCKQUOTE>


Is that right?? to Manifold?? then at idle you would have the advanced cranked. And it would let off as you increased rpm..

Isnt that vacuum retard?

[JOECOOL]

hehe Nograin. When I first registered last year I went blank when I needed a screen name so I used my name. But if I changed it I would lose all my stars.
OH I didnt realize I deleated the road warrior qoute. Musta messed it up when I was trying to add something there and my screen froze up. I'll put it back on when I get home tonight. I discovered how to post pictures last night and was having fun.

[porkchop]

Well my nieghbor that works at a local car dealership as a mechcanic came over tonight as I was playing with my carb. He told me that because I have a hot cam, 272 intake 282 exhaust I will never get a steady vacum at idle. He helped me adjust it to the point that I get a good response on the pedal. I also have no black smoke coming out of the exhaust so the adjustments are great. Is this true? Or was he blowing smoke up my butt? It runs good just not at idle.

[JOECOOL]

Maybe, depending on your cam. BUT Your vacuum readings are too hight to be the cam (I think). Longer duration cams will lower your vacuum readings. Didnt you get more of a RV grind cam? On my 69 Impala woth a hot 400 I could barley pull 10 hgs of vacuum but it still gave me ok readings.
BTW try raising your timing a little. I usally run 13-14 BTDC when I run hotter cams on my old muscle car.
your running stock timing on a non stock cam.
Heck I couldnt even get my 360 Dodge to IDLE below that timing with the cam I put in it.

[nograin]

I see Rudy - you got the new handle working now :D

PC
I'm with Rudy here.
I'm running the comp cams 280 degree cam in my 340. Once its warm, my idle vacuum is around 14, and it bounces less than 1". Your split duration cam is about the same - I think the lift on the 280 cam is .454 but I'ld have to look.

Now, I did say that was WARM. Cold it darn near dies, but I don't have the choke hooked up. Also, I cheated and put in Rhoads lifters and later on an MSD 6T.

Its the 5 turns out thing that bothers me a bit. That seems like a lot.

Yea. The timing thing. I didn't know you had a non-stock cam. You can just about forget the specs then, you've got to create your own now. Soooo, advance it a bit at idle.
To make sure you are reading the same thing each time.
a) Get your readings with the vac advance disconnected and the vacuum line plugged. (Add vacuum advance then the reading will change with change in vacuum)
b) record the RPM the reading was at. Try to keep that the same. Centrifigal advance increases with rpm.

The way to set your basic advance is a wide open throttle run under load (High gear - ip hill) If it pings at all, reduce the timing. Ideal advance is usually figured to be just about 3 degrees less than when it pings.

If you have a buddy, you can actually set the timing at full advance if you have timing marks to high enough or a dial back timing light. Basically you run the engine at 3000 rpm briefly and read the timing (no vacuum advance here) Most distributors are fully advaced by 3000. If you don't do it this way, its OK. The relation between idle advance and full advance is usually pretty constant.

Let me explain that last sentence. If your timing a 600 rpm is 10 degrees, and your centifigal advance has a total of 25 degree between 800 and 2500 rpm. Then at 2500 up, you timing is at 35 degrees (10+25). If you change the initial advance from 10 to 12 degrees at 600 rpm, then at 2500 its going to be 25 plus the 12 = 37 degrees total.

Racers sometimes have to read it at the total because advance curve may already be started at idle. Say you idle at 1200 rpm, and the curve started at 800 (that is the weights move out) then even though you move it from 10 to 12 degrees, you don't know how much more of the curve is left, just that its not 25 degrees.

Hope that helps and not makes you
:confused:

Also, the point I made before about ported vacuum is not needed - Still true! smile.gif

[porkchop]

I think I understand what you are saying. I am going to read through it a couple more times and then give it a try this weekend. Thanks.

[nograin]

Here's what an advance curve looks like.
This mechanical advance only. It depends entirely on rpm. When the rpm is high enough, it overcomes the spring force and the weights start to move out, and that mechanically shifts the rotor x degrees. Where you set the initial timing does not effect the shape of the curve. It just means the starting point is above (or below) zero, and the whole curve will shift up or down the same amount.

http://users.erols.com/mathewg/adv.gif

In reality, there is usually some continued drift out, even once it is "fully advanced", and thats how I drew it here.

[porkchop]

Thanks that helps me out. I am pretty sure that my dizzy is shot though. I was playing with it again tonight and decided to check the vacum on the advance and it would not hold the advance in place :( I am going to get a new dizzy and then try again. Thanks for all the help everyone, especially nograin!