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Vaccum gauge bouncing ...
#1679662
09/29/14 01:27 AM
09/29/14 01:27 AM
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JohnRR
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Friend that I am helping out 383 has all of a sudden started to run poorly. After checking to make sure the cam isn't going flat he got it back together and I start see whats going on , he adjusted the timing without a light  Anyway when it's idling at about 900 rpm the vac gauge at the base of the carb has the needle fluctuating wildly, 10" or more, bring the RPM up to about 2k and the needle smooths out ? The engine is fresh and it was running well till the other day it just started running poorly, carb is a fresh rebuilt Holley 650 DP that's about 30 years old. I'm a little stumped and don't want to tear the thing apart further than necessary, a search online says sticky valves or a vac leak??? I sprayed starting fluid around the carb and intake thinking big vac leak but that turned up nothing ? There are paper gaskets on either side of the valley tin.
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Re: Vaccum gauge bouncing ...
[Re: GTX MATT]
#1679669
09/29/14 12:32 PM
09/29/14 12:32 PM
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JohnRR
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Quote:
If it smooths out when you rev it up common wisdom is that its really loose valve guides. Never seen an engine do it though, anything I've seen is a burned valve or another issue and it never smooths out. I'm not sure how loose they would need to be to cause this. 
Heads have new valves and bronze liners, Comp springs, so I can't see it being the heads, especially consider who I had do the heads. It does have adjustable pushrods I can to adjust them again to rule out a valve hanging open. The weird thing is it was running so good, cam break in was perfect without any hiccups ...
I had the valve covers and the intake off and everything looked good, rotated the engine over to make sure everything was working fine.
Decks on both the heads and the block are fresh, Felpro 8519 gaskets. I hope it's not a head gasket because the block or head surface is probably torched by now ... uuugggghh
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Re: Vaccum gauge bouncing ...
[Re: JohnRR]
#1679670
09/29/14 12:53 PM
09/29/14 12:53 PM
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Joined: Jun 2006
Posts: 5,163
CT
GTX MATT
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Posts: 5,163
CT
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Head gasket should just read erratic no matter what in my opinion.
If you trust the machine work I'd say look into ignition and fuel, another carb if you can try it. Smell rich/funny??
Now I need to pin those needles, got to feel that heat
Hear my motor screamin while I'm tearin up the street
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Re: Vaccum gauge bouncing ...
[Re: GTX MATT]
#1679671
09/29/14 01:14 PM
09/29/14 01:14 PM
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Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
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Assuming that is the problem (HG), At higher RPM's the head gasket is still blown obviously but the firing pulses being closer together masks/distorts the reading showing on the gauge
live every 24 hour block of time like it's your last day on earth
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Re: Vaccum gauge bouncing ...
[Re: JohnRR]
#1679672
09/29/14 01:49 PM
09/29/14 01:49 PM
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Joined: Mar 2003
Posts: 4,848
Memphis
HemiRick
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master
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Memphis
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Do a compression test, it will find the problem.
Take care,
Rick
68 Coronet R/T 440 & 68 Charger 528 Hemi,and 5 Challengers! 6 cyl, 318, 360, 383, 451
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Re: Vaccum gauge bouncing ...
[Re: GTX MATT]
#1679673
09/29/14 02:16 PM
09/29/14 02:16 PM
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Joined: Jan 2003
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U.S.S.A.
JohnRR
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Quote:
Head gasket should just read erratic no matter what in my opinion.
If you trust the machine work I'd say look into ignition and fuel, another carb if you can try it. Smell rich/funny??
Changed out the distributor from a pertronics to points , didn't change anything, I moved the timing light onto all the plug wires and everyone is firing. I have a set of firecore wires I'm going to swap on to rule that out, bypassed the ballast and didn't change anything.
All he has is old, ugly carbs, it might be the carb on is so I guess I'm either going to have to buy one to try or use my new Thunder series 800. He's retired/fixed income and can't afford to buy new parts.
Compression test is first order of business.
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Re: Vaccum gauge bouncing ...
[Re: stumpy]
#1679675
09/29/14 04:11 PM
09/29/14 04:11 PM
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JohnRR
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Quote:
Did you try pulling the plug wires one at a time as was suggested earlier? Throwing parts at it isn't the cure. You need to do the basic diagnosis first.
Thanks for your help Stumpy , I know I can always count on you 
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Re: Vaccum gauge bouncing ...
[Re: feets]
#1679678
09/29/14 05:58 PM
09/29/14 05:58 PM
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JohnRR
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Quote:
Quote:
John no harm intended but this is kinda refreshing seeing you with a problem and not a solution!!!!
Ron
A common issue is being too close to the problem.
Sometimes the answers come when you haven't been working on it.
I've got a good idea as to what it may be , the problem is in order to change out the offending part to prove that it is bad I'm the one that will have to supply the parts ... he's worked in a junkyard most his life and that is where his spares .... and sadly his storage techniques .... come from ... I asked for an iron intake to put on the motor to cover it up before we could get it installed in the car and he brings be one that is full of dirt ...
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Re: Vaccum gauge bouncing ...
[Re: stumpy]
#1679680
09/29/14 07:57 PM
09/29/14 07:57 PM
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JohnRR
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Quote:
JRR I was just wondering if you had isolated the problem because you didn't say in your post. You just listed parts you had changed. 
I listed a bunch of parts ... the engine is a fresh build with maybe a couple hundred miles on it ... but the only part that was changed out was the distributor and that was because the owner is stuck in the 60's and doesn't like electronic ignition. I was concerned that maybe the the Pertronics and/or the Pertronics coil was damaged because it was being run with the ballast resistor still in place.
If you know of a way to test the Pertronics without replacing it with something else I'm all ears ...
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Re: Vaccum gauge bouncing ...
[Re: JohnRR]
#1679681
09/29/14 08:53 PM
09/29/14 08:53 PM
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Joined: Oct 2005
Posts: 1,305
Lakewood, Colorado
herkamer
pro stock
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pro stock
Joined: Oct 2005
Posts: 1,305
Lakewood, Colorado
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My brother put a Pertronix conversion in his M37 and pinched a wire direct to ground. He was worried about it and called tech support. Guy told him if it was working, then all is well. They generally work or don't.
Matt
69 Dart Swinger 340
83 W350, Megasquirted with 46RH
Old news: 72 Demon street/race mobile
Latest: 70 Duster backhalf car
and even more
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Re: Vaccum gauge bouncing ...
[Re: stumpy]
#1679683
09/29/14 10:37 PM
09/29/14 10:37 PM
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Joined: Jan 2003
Posts: 15,411
Omaha Ne
TJP
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I Live Here
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Omaha Ne
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Quote:
You still haven't told us what happened when you unplugged one wire at a time which will isolate a bad cylinder in case it isn't a carb problem. Just because all the parts are new doesn't mean one couldn't have failed.
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Re: Vaccum gauge bouncing ...
[Re: stumpy]
#1679685
09/30/14 04:31 AM
09/30/14 04:31 AM
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JohnRR
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Quote:
Just because all the parts are new doesn't mean one couldn't have failed.
No [Edited by Moparts - Family Friendly Site - Keep it clean]'
again , thanks for nothing
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Re: Vaccum gauge bouncing ...
[Re: ahy]
#1679686
09/30/14 04:32 AM
09/30/14 04:32 AM
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JohnRR
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Quote:
I wonder if its possible you got ported vacuum? Sounds silly but wouldn't hurt to check another port... maybe same one as the brake booster.
No , it's a holley carb , it was on the base.
Thanks to everyone that was helpful, it'll be a few weeks before I have the time to get back to it.
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Re: Vaccum gauge bouncing ...
[Re: JohnRR]
#1679687
09/30/14 06:46 AM
09/30/14 06:46 AM
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Joined: Sep 2004
Posts: 523
Right here
HP2
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mopar
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Right here
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An useful site for vacuum reading is http://www.secondchancegarage.com/public/186.cfm If you are running a hot cam things changes. It's impossible to get a steady needle at lower rpm's, so how do you determine what power valve to put in your Holley?
70 W100 Power Wagon. 318 4-spd
70 Sport Fury 440 2dr HT
71 Duster 340
71 Charger Super Bee - 383/727
72 Charger "Sabotage" - 440/727 - Street/Strip
78 Warlock in beautiful patina
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Re: Vaccum gauge bouncing ...
[Re: HP2]
#1679689
09/30/14 12:05 PM
09/30/14 12:05 PM
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Joined: May 2003
Posts: 15,487
Florida
scratchnfotraction
I Live Here
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I Live Here
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Florida
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Quote:
An useful site for vacuum reading is http://www.secondchancegarage.com/public/186.cfm
If you are running a hot cam things changes. It's impossible to get a steady needle at lower rpm's, so how do you determine what power valve to put in your Holley?
thanks, that was indeed an interesting read on the vac readings.
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Re: Vaccum gauge bouncing ...
[Re: JohnRR]
#1679690
09/30/14 02:03 PM
09/30/14 02:03 PM
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Joined: Jan 2003
Posts: 32,943
Grand Prairie,Texas
stumpy
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Grand Prairie,Texas
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Quote:
Quote:
Just because all the parts are new doesn't mean one couldn't have failed.
No [Edited by Moparts - Family Friendly Site - Keep it clean]'
again , thanks for nothing
What is your problem?. I have done nothing but try to suggest things to help and you come back with garbage aimed at me. If my advice bugs you so much then put me on ignore.
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Re: Vaccum gauge bouncing ...
[Re: HP2]
#1679691
09/30/14 04:19 PM
09/30/14 04:19 PM
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U.S.S.A.
JohnRR
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Quote:
An useful site for vacuum reading is http://www.secondchancegarage.com/public/186.cfm
If you are running a hot cam things changes. It's impossible to get a steady needle at lower rpm's, so how do you determine what power valve to put in your Holley?
Thanks I'll check it out.
As I was trying to fall asleep I remembered something that happened while turning the engine over to inspect the cam while the intake was off , it's either a head gasket or a bent intake valve.
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Re: Vaccum gauge bouncing ...
[Re: JohnRR]
#1679692
09/30/14 05:06 PM
09/30/14 05:06 PM
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Joined: Jan 2003
Posts: 6,224
JERSEY
RJS
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JERSEY
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Quote:
Quote:
An useful site for vacuum reading is http://www.secondchancegarage.com/public/186.cfm
If you are running a hot cam things changes. It's impossible to get a steady needle at lower rpm's, so how do you determine what power valve to put in your Holley?
Thanks I'll check it out.
As I was trying to fall asleep I remembered something that happened while turning the engine over to inspect the cam while the intake was off , it's either a head gasket or a bent intake valve.
I was poking you with a stick just for fun, You know your still the coolest right???
Ron 
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Re: Vaccum gauge bouncing ...
[Re: RJS]
#1679693
09/30/14 07:03 PM
09/30/14 07:03 PM
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Joined: Jan 2003
Posts: 75,043
U.S.S.A.
JohnRR
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Quote:
I was poking you with a stick just for fun, You know your still the coolest right???
Ron
I'm far from the coolest ... 
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