Team Camaro Tech banner

1 - 20 of 45 Posts

·
Registered
Joined
·
127 Posts
I started a thread for the no spark issue, and it got resolved. :thumbsup:

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.

:beers:
 

·
Registered
Joined
·
1,470 Posts
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 ?
 

·
Moderator
Joined
·
14,083 Posts
Re: New enfine, very little vacuum, help!!!

Which port are you hooking your vacuum gauge to?
 

·
Premium Member
Joined
·
11,167 Posts
Re: New enfine, very little vacuum, help!!!

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.
 

·
Registered
Joined
·
127 Posts
Discussion Starter #5
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!;)
 

·
Premium Member
Joined
·
11,167 Posts
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?
 

·
Moderator
Joined
·
14,083 Posts
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.
 

·
Registered
Joined
·
127 Posts
Discussion Starter #8
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.
 

·
Registered
Joined
·
127 Posts
Discussion Starter #10
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?

:beers:
 

·
Premium Member
Joined
·
11,167 Posts
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?

:beers:
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.
 

·
Registered
Joined
·
127 Posts
Discussion Starter #12
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.
 

·
Premium Member
Joined
·
11,167 Posts
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
 

·
Admin/Super Moderator
Joined
·
12,511 Posts
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.
 

·
Premium Member
Joined
·
11,167 Posts
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.
 

·
Registered
Joined
·
127 Posts
Discussion Starter #16
Hey everyone, thanks for the replies so far. Let me try and better explain myself.

This is a new engine that is part of a complete restoration, most of the car has yet to be assembled. There is nothing vacuum related hooked up to the engine, I have removed everything possible and plugged all the ports, except for the PCV valve. I'm using the RS vacuum port as my source for my vacuum gauge (full manifold vacuum). I haven't tried hooking up the vacuum line to the distributor yet. I wanted to get more vacuum from the engine before I hooked up the distributor advance. Today, I'll check the PCV hose for leaks. Also, is it possible to have a vacuum leak within the carb? The carb is a rebuilt original carb for the 302. But, as I learned with the new distributor, just because it's new, doesn't mean it works properly.

Thank You very much for your help so far, please keep the suggestions coming.
 

·
Admin/Super Moderator
Joined
·
12,511 Posts
Chris - Yes if the carb is not sealed to the intake correctly or any of the layers of the carb are not tight leaks could occur. If you have a propane torch, weep a little propane around the base and sides while the engine is running, if you get an uptick in RPM's you have a vacuum leak in the area. You can use starter fluid but it might damage your paint.
 

·
Moderator
Joined
·
14,083 Posts
automatic car? Check the tube to the vacuum mod on the tranny

Also confirm plug wires are on correct position firing order
 

·
Registered
Joined
·
127 Posts
Discussion Starter #19
I did try the propane bottle with a hose all over the intake and carb, I didn't notice any difference in RPM.

The car has an M21 four-speed, so no vacuum lines there.
 

·
Premium Member
Joined
·
11,167 Posts
Hey everyone, thanks for the replies so far. Let me try and better explain myself.

This is a new engine that is part of a complete restoration, most of the car has yet to be assembled. There is nothing vacuum related hooked up to the engine, I have removed everything possible and plugged all the ports, except for the PCV valve. I'm using the RS vacuum port as my source for my vacuum gauge (full manifold vacuum). I haven't tried hooking up the vacuum line to the distributor yet. I wanted to get more vacuum from the engine before I hooked up the distributor advance. Today, I'll check the PCV hose for leaks. Also, is it possible to have a vacuum leak within the carb? The carb is a rebuilt original carb for the 302. But, as I learned with the new distributor, just because it's new, doesn't mean it works properly.

Thank You very much for your help so far, please keep the suggestions coming.
Morning, vacumn leak within the carb could be between the air horn and base, there are screws under the base, one could have been left out. There are normally 6. The gasket between needs to match all holes. This gasket can be put on backwards. An alignment pin makes sure its done right. Just pull and check.
How about the little cork gasket between the secondary diaphragm? Is it there? Have to pull diaphragm body off to check. there should be 3 screws holding this and I think one goes into the venturi .
You still need to verify that you are on #1 tdc at dist. If you are, then move on the rechecking valve lash.
Here are some photo of the base, .
 

Attachments

1 - 20 of 45 Posts
Top