Vacuum Gauge Reading , What Does It Mean ?

[A20A1]

More help.



Connect Gauge to either #6 or #20 depending on which vacuum port isn't being used... an unused vacuum port should have a vacuum 'Cap' or 'Plug' over the port. Remove the air cleaner to gain access to the ports... but reinstall the air cleaner before doing your testing.

[A20A1]

# 11 Choked cat or muffler more like

[steveko]

Idle 900-1000rpms vaccum needle 19/1/2 to 20''
Off idle 2300rpms 21 to 22''
what could the needle be fluctuating from possibly to lean a mixture setting?

The reason I say this is because my plugs usually look whiteish too light gray.
and at about 2000rpms up there's no real power.
I have to mention that I have replaced the air filter with a K&N .
Also the exhaust is maybey 1/2'' bigger from the cat back.

This is my source of irritation.

Please Help.

[A20A1]

1 point off the guage isn't something to worry about though.
There isn't always a suction wave, and sometimes their may even be some reversion.


If you're not getting enough fuel Check for:

Vacuum Leaks
Booster Venturies Loose
Fuel Filter Dirty
Float Level Low
Carburetor Dirty
Fuel Pump Dying, or Electrical Power to Fuel Pump Low.

[steveko]

I think out of all of the things listed it could be possibly Fuel Pump power or Voltage at the pump or a dirty high speed jet or something. All the other things have been replaced last summer. and or adjusted I just last weekend Tightened up the primary booster and replaced the O ring gasket. Secondary booster leg was tight with no apparent leakage. Also the fuelpump was replaced about 2 years ago.

[steveko]

Hey what about a faulty carb adjustment as stated in pic 3 although not a wide fluctuation as stated above?

[A20A1]

Their might be something wrong with the solenoids or sensors for the carb and the air suction system.

Have you checked the O-2 Sensor?

You could also try adjusting the float a little, becareful because if can break an o-ring easily and begin to leak.

Don't touch the A/F screw unless it's falling out or something.

[steveko]

I've checked the O2 sensor last year from the control module under the seat and it checked out ok. The air suction system I'll have to look up in the manual too see what's involved with it. Unless your talking about the PCV valve.

[CAMARORZ28]

hey guys i have a reading of #6 and what could be a #9 , the car idles in #6 just about point 10 and then it goes up it keeps constant about 15 and 20 and then it goes down to 10 and then up again. it says valve springs are weak, but on #9 it also says it vibrates while idling, what does this mean?? and the needle does keep steady as the speed is increase, hope i get some feedback thanks ya

[LX-incredible]

Rapid needle fluctuations are the result of valves sitcking / not properly seating. Is the needle fluctuating or not?

[CAMARORZ28]

fluctuating? you mean if the needle is constantly moving up and down from 10 to about 20 yes it is, if valves are sticking what can i do?

[A20A1]

it says springs are weak... so you replace the springs... might want to check your valve lash just in case.

https://www.3geez.com/forum/showthread.php?t=39319

[CAMARORZ28]

so the website you showed me shows me how to adjust the valves, is there another page were i can change the springs??? how much would i be spending on springs, would ya suggest me to just buy a new car? how much time i'm going to be spending on changing springs, adjusting valves, is it worth the time spend?

[ghettogeddy]

so the website you showed me shows me how to adjust the valves, is there another page were i can change the springs??? how much would i be spending on springs, would ya suggest me to just buy a new car? how much time i'm going to be spending on changing springs, adjusting valves, is it worth the time spend?

prolly gona be a couple hunered bucks its like 360 or so for new spring rockers and everthing else in the valve train so springs arent to much heres a post from my own rebuild thread that shows the prices for some a18 parts thats are better then stock and fit without modificatopn
https://www.3geez.com/forum/showpost....0&postcount=52

[A20A1]

On another note I would try to rule out other possibilities like spakplugs or faulty carb adjustment or vacuum leaks that could be hiding behind an increased idle speed, if idle was adjusted to compensate over the years.

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BTW

#9 vibrates at idle 800-1000 rpm
But when you raise the rpm from say 1000 rpm to 3,000 rpm the flucuation of the pointer will begin to stop.

#6 is steady at idle 800-1000 rpm, no fluctuation
But when you raise the rpm from say 1000 rpm 3,000 rpm then the needle fluctuates.

If it only fluctuates at idle 800-1000 rpm then that would mean #3

If it fluctuates at any rpm then that would mean #12

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[CAMARORZ28]

On another note I would try to rule out other possibilities like spakplugs or faulty carb adjustment or vacuum leaks that could be hiding behind an increased idle speed, if idle was adjusted to compensate over the years.

.
.

BTW

#9 vibrates at idle 800-1000 rpm
But when you raise the rpm from say 1000 rpm to 3,000 rpm the flucuation of the pointer will begin to stop.

#6 is steady at idle 800-1000 rpm, no fluctuation
But when you raise the rpm from say 1000 rpm 3,000 rpm then the needle fluctuates.

If it only fluctuates at idle 800-1000 rpm then that would mean #3

If it fluctuates at any rpm then that would mean #12

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ok the car when i first want to start it and its cold i have to step on the gas pedal to give a little gas, otherwise it will just wont to start until many attempt and then it starts without pressing on the gas. then when the car starts it starts to accelerate "without me pressing on the gas" , and it goes up to 2500 rpm and it stays there for a while, if i dont press on the gas sligtly it will not decrease from 2500 rpm, when i press on the was sligtly it decreases to about 1500 rpm, and then about 1 minute from beign in 1500 rpm it goes up to 1100 rpm, after a few minutes then the car starts to idle, from about 700 to 1000 rpm, then from about 500 rpm to 1000, and so for, and if i dont keep it steady at the gas "meaning feeding it gas so that it does'nt idle from about 500 to 1000" the car will shut off but it will start right back up.

[CAMARORZ28]

prolly gona be a couple hunered bucks its like 360 or so for new spring rockers and everthing else in the valve train so springs arent to much heres a post from my own rebuild thread that shows the prices for some a18 parts thats are better then stock and fit without modificatopn
https://www.3geez.com/forum/showpost....0&postcount=52

if that was the case, could i get the head from a junk hard and that way i dont have to do all the valve spring changing? i know i could be risking that the head is bad but could i give it a try?

[A20A1]

So you're sure you don't have a vacuum leak then, it sounds like it not even looking at a vacuum gauge but then a leaky valve would do the same thing.

Check for leaks try to get it to idle without help from you.

it's a lot easier to check for leaks then it is to replace the head... might save you a lot of work if it's just a vacuum leak and not the valve(s).

high idle (fast idle) on startup is normal and so is pressing the gas to get the rpm to drop. If you need help getting the car to idle check out this thread,

https://www.3geez.com/forum/showthread.php?t=46572

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[lostforawhile]

I finally scanned some info from a vintage chiltons book,this is the vaccume gauge readings question answered,now i can't find the thread. if someone can locate it,eithier move this,or add a link please. i searched with no good as expected. i'm really suprised they don't put this info in modern service manuals,the info is just as relevant on modern engines as on vintage engines.

[MessyHonda]

i believe a20a1 posted the link topic on vacuum....nice find Tim

[lostforawhile]

that is from a 1962 mg tune up guide, there is also a lot of interesting general information on engine rebuilding,tuning,carb info etc. a lot of it applies very well to any carbed engine. also info on porting and ccing cylinder heads,etc. you just can't find this kind of info anymore. i will scan as soon as i get the chance. i need to make photo copies,they scan better.

[A20A1]

I like your diagrams more and the descriptions.

[lostscotiaguy]

To : Camaror
"ok the car when i first want to start it and its cold i have to step on the gas pedal to give a little gas, otherwise it will just wont to start until many attempt and then it starts without pressing on the gas. then"

I second that response from A20A1.... High startup idle is normal in any carburated vehicle, and 2500 sounds about right. It will do this until it warms up and then it should drop automatically to around 750.... Your best bet is when you go to start it when it's cold is to push the pedal 1-2 times to the floor BEFORE turning it over, then just turn it over, it should start right up and then go into "high idle". If you tap the throttle and do the "Kick down" before the car is up to temp it will usually want to stall out and will feel sluggish. This is just because the fuel wont evaporate as easily/quickly on a "cold" throttle plate, and will make it harder for the engine to run properly.
Anyhow i hope this helps and I'm probably telling you stuff you already know, but I figured I'd throw my 2 cents in...

I feel old! I can remember a time before Fuel Injection when "Warming up the car"was just one of those hassles you had to deal with before driving somewhere. Now when I wait for my 81 to warm up I kind of enjoy it, but I do hate the idea that you have to rev the crap out of a cold engine.