New engine, very little vacuum, help!!! - Team Camaro Tech
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post #1 of 45 (permalink) Old Aug 21st, 14, 03:57 PM Thread Starter
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Chris
 
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New engine, very little vacuum, help!!!

I started a thread for the no spark issue, and it got resolved.

Now I have a problem with very little vaccum, 5" or less at idle. So far I have;
*Re-torqued the intake manifold and carb.
*Unplugged everything hooked up to a vacuum source and plugged the intake/carb vacuum fittings
*Set the timing to 14*, and idle speed to 1000RPM
*Used a propane torch all over the intake and carb, no change in idle.
*Did a compression test, all cylinders between 190-210 PSI.
*Adjusting the idle/air screws doesn't have any effect unless I close them, then the engine dies.

Any suggestions would be great.


1969 Z28 RS (building)
DZ302
M21
12-bolt, 3.73


Last edited by Vega$69; Aug 21st, 14 at 05:56 PM.
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post #2 of 45 (permalink) Old Aug 21st, 14, 04:12 PM
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Re: New enfine, very little vacuum, help!!!

In your other thread you said :
Taking the vacuum hose off the distributor while running didn't change the vacuum reading?!
------------
Be sure the vacuum can is working. Is it plugged into full manifold vacuum ? It should have suction when the engine is idling.

Where on the carb is the vacuum line from the distributor attached ?

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post #3 of 45 (permalink) Old Aug 21st, 14, 05:55 PM
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Re: New enfine, very little vacuum, help!!!

Which port are you hooking your vacuum gauge to?

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post #4 of 45 (permalink) Old Aug 21st, 14, 06:40 PM
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Re: New enfine, very little vacuum, help!!!

Quote:
Originally Posted by Vega$69 View Post
Which port are you hooking your vacuum gauge to?
Also, whats vacumn right off manifold ? You do have a 2 or 3 way tee there don't you?
Where is your brake booster pulling from? If you have a hole on the booster diaphragm or check valve or a leak in the booster line, you may be loosing vac. Try to isolate vacumn points.

Don
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post #5 of 45 (permalink) Old Aug 21st, 14, 06:46 PM Thread Starter
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Re: New engine, very little vacuum, help!!!

I'm hooking my vacuum gauge to the vacuum tee on the back of the intake manifold. One side of the tee goes to the brake booster, and the side I'm using for now will supply vacuum for the RS headlight system.

The vacuum advance is hooked to a port on the bottom right side of the carb. The fitting points straight out to the right side of the car, it's the only vacuum port on the carb. (I'm using a rebuilt original carb). One thing I did notice today was that this port seems to be blocked. There is no vacuum from it, and with the vacuum hose hooked to it, I can't even blow through it. I did hook this same hose to the distributor, and sucking on the other end moves the advance plate in the distributor.

Myself and the car owner are starting to wonder if maybe the intake is not sealing properly against the heads. We've both read posts here about that problem, and today I noticed what looked like oil laying at the edge of the intake where it meets the cylinder head at the exhaust crossover port. I'm willing to check everything again, and anything else before I have to go and pull the intake manifold back off. The engine looks so pretty right now, I don't want to spoil it!

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post #6 of 45 (permalink) Old Aug 21st, 14, 07:00 PM
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Re: New engine, very little vacuum, help!!!

Unless John has an idea, I am asking if you know what manifold vacumn is and ported vacumn is.
Some ports on the carb , do not have vacumn until the throttle plates are opened , thus allowing vacumn to the dist.
There should be a port on that holley, in the right front corner of the carb base, that's where you get manifold vacumn for the dist. You said a rebuilt carb? Number ?

Fact you have 5" vac at the rear tee, tells me something else. Any chance you got valves too tight? I know you said you adjusted to .030+-, but that is still good for a solid.

Just wondering if you have the dist off 180, I have seen that and the motor will run but not good.

Might bring #1 cly up to tdc and pull cap off to see where rotor is pointing. its easy. I mean, something not right here, gotta look.

Oh, whats the pcv valve line doing? off the back of the carb base?

Don
TC # 349
Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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post #7 of 45 (permalink) Old Aug 21st, 14, 07:06 PM
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Re: New engine, very little vacuum, help!!!

Disconnect and plug the line to the brake booster. Maybe a bad leak in the booster.

Next I'd look at the intake. A friend of mine recently changed his intake and it was slightly off center when he torqued it down one side was on the ridge of his heads. He was sucking air from the valley.

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post #8 of 45 (permalink) Old Aug 21st, 14, 07:30 PM Thread Starter
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Re: New engine, very little vacuum, help!!!

Quote:
Originally Posted by zdld17 View Post
Unless John has an idea, I am asking if you know what manifold vacumn is and ported vacumn is.
Some ports on the carb , do not have vacumn until the throttle plates are opened , thus allowing vacumn to the dist.
There should be a port on that holley, in the right front corner of the carb base, that's where you get manifold vacumn for the dist. You said a rebuilt carb? Number ?

Fact you have 5" vac at the rear tee, tells me something else. Any chance you got valves too tight? I know you said you adjusted to .030+-, but that is still good for a solid.

Just wondering if you have the dist off 180, I have seen that and the motor will run but not good.

Might bring #1 cly up to tdc and pull cap off to see where rotor is pointing. its easy. I mean, something not right here, gotta look.

Oh, whats the pcv valve line doing? off the back of the carb base?

Sorry about that, I guess I wasn't clear. Yep, I know about ported and manifold vacuum. The distributor needs manifold vacuum. I had the distributor advance hooked to the port you're referring to. That' also the one that seems to be blocked? If it is in fact a manifold vacuum port, it should be open all the time, correct?
I currently have all the vacuum ports plugged except the PCV, I'll check that one tomorrow.


The kicker is that the engine seems to be running fine? It starts, idles, and revs easily.

1969 Z28 RS (building)
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post #9 of 45 (permalink) Old Aug 21st, 14, 07:31 PM
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Re: New engine, very little vacuum, help!!!

Do what John suggested before you go further, you may have two issues and need more vacumn than 5"

Don
TC # 349
Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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post #10 of 45 (permalink) Old Aug 21st, 14, 07:33 PM Thread Starter
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Re: New engine, very little vacuum, help!!!

i thought about the valves possibly being too tight (not sealing) as well. But I thought that would show up as low compression in the compression test?


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M21
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post #11 of 45 (permalink) Old Aug 21st, 14, 07:59 PM
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Re: New engine, very little vacuum, help!!!

Quote:
Originally Posted by Z28BUILD View Post
i thought about the valves possibly being too tight (not sealing) as well. But I thought that would show up as low compression in the compression test?

When running a comp test, you have a check valve in the gauge, thus holding the psi as the cly pressures. Only way I have tested valve sealing was with my leak down tester but that involves taking all spring tension off valves and pressuring up , then monitoring the rate of leakage on the gauge.

valves too tight will do what is happening to you. But you sound like you got that cleared up. If you are not sure, then adjust valve the old way, one valve up and one down, then move to next cly. make sure you go thru the open close sequence and your rocker is loose. easy to do, old school.

only other thing I am thinking of is, first , is your vac gauge accurate?
Second, can you run a vac hose from your 5" point of read to the dist advance and see what that does? Motor should speed up as you rev motor some.
Last, did you do what John said on the booster line plugging? Eliminate all possible leak points, I had a bad booster diaphragm at one time also, this is just like a big vac leak.

Try it.

Don
TC # 349
Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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post #12 of 45 (permalink) Old Aug 21st, 14, 08:28 PM Thread Starter
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Re: New engine, very little vacuum, help!!!

Quote:
Originally Posted by zdld17 View Post
When running a comp test, you have a check valve in the gauge, thus holding the psi as the cly pressures. Only way I have tested valve sealing was with my leak down tester but that involves taking all spring tension off valves and pressuring up , then monitoring the rate of leakage on the gauge.

valves too tight will do what is happening to you. But you sound like you got that cleared up. If you are not sure, then adjust valve the old way, one valve up and one down, then move to next cly. make sure you go thru the open close sequence and your rocker is loose. easy to do, old school.

only other thing I am thinking of is, first , is your vac gauge accurate?
Second, can you run a vac hose from your 5" point of read to the dist advance and see what that does? Motor should speed up as you rev motor some.
Last, did you do what John said on the booster line plugging? Eliminate all possible leak points, I had a bad booster diaphragm at one time also, this is just like a big vac leak.

Try it.
Ok, I didn't realize that about the compression test. I do have the brake booster unhooked and the side of the T-fitting where it hooks on the back of the intake is plugged. I have had the vacuum advance unhooked (and plugged) the whole time.

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post #13 of 45 (permalink) Old Aug 21st, 14, 08:36 PM
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Re: New engine, very little vacuum, help!!!

Quote:
Originally Posted by Z28BUILD View Post
Ok, I didn't realize that about the compression test. I do have the brake booster unhooked and the side of the T-fitting where it hooks on the back of the intake is plugged. I have had the vacuum advance unhooked (and plugged) the whole time.
what are you saying? motor responded to manifold vac to dist? connect motor vac to advance and see if motor speeds up thus engine vac read comes up

Don
TC # 349
Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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post #14 of 45 (permalink) Old Aug 21st, 14, 08:40 PM
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Re: New engine, very little vacuum, help!!!

An older vacuum headlight set of hoses is going to leak, I would pull the lead, plug or cap the port and continue on and see if your readings improve with both brakes and headlights capped.


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post #15 of 45 (permalink) Old Aug 21st, 14, 08:44 PM
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Re: New engine, very little vacuum, help!!!

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Originally Posted by 69-Pace View Post
An older vacuum headlight set of hoses is going to leak, I would pull the lead, plug or cap the port and continue on and see if your readings improve with both brakes and headlights capped.
Brian, good point, having an RS car, I had that over last 45 years including the relay slider valve as well as the door motors or cans.. . , just trying to get all possible leak sources disconnected and tested as an engine only. You are correct.

Don
TC # 349
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