Common Vacuum Leaks Help

My 59 cj5 has ran fine and driven weekly for 3 years no problems. Now it runs fine but doesn't idle well all of a sudden and set timing with a timing light, timing is fine. Checked with vacuum gauge and vacuum is very low at idle it's only 8 inches of vacuum floor it and it turns to 0. I sprayed carb cleaner around carb and hardlines and fittings leading to the pcv and can't find any vacuum leaks. What other places should I check for leaks? I have a F head 134 engine and it has an original AC 4693 fuel/vacuum pump that I had purchased NOS off ebay about 3 years ago and I normally run E10 fuel Is it possible my vacuum is leaking from inside the fuel/vacuum pump and vacuum is leaking into the crankcase? If that's possible how would I check that?

 

The vacuum pump diaphragm may indeed have failed, and the manifold could be pulling air/fumes from the crankcase.

I suppose I would start by disconnecting the suction side of the pump and put a vacuum gauge on it - see if it sucks, so to speak.

And/or remove the vacuum tube below the carb, plug that port, and see if the engine performance returns to normal.

 

so I removed the hard line under the carb that leads to the fuel pump. and installed a barbed fitting to attach my vacuum gauge directly under the carb and I could get 19 inches vacuum at higher rpms but couldn't get an idle reading because it wont stay running at idle even with the line under carb detached (but the line was then just hanging open where it had been attached to the manifold. and the other side of that hardline that led to the a T which then leads to the pcv valve and to the pump were all still attached.) did I need to block off any of this stuff too?

I also removed the fuel line that leads from the fuel pump to the carb and attached my fuel vacumm gauge to see what my pump was making for fuel pressure and it stayed steady at 4 psi which I think is high for my carter carb but it does have one spacer installed on it already. I revved the engine and it never strayed off 4 psi even at higher throttle or blipping the throttle, always 4 psi. then when the engine died because the carb ran out of fuel the gauge still showed 4 psi fuel pressure even after dying and I left it for about 1 minute before removing the gauge and it hadn't dropped yet.

right now I'm wondering if there is a vacuum leak I cant find since it still wont idle with hard line under carb detached and gauge installed in its place. or if maybe theres like an idle jet plugged in the carb. it has a plastic modern fuel filter installed before the pump that should have been keeping crud out.

I had heard of a old mans trick of getting rpms up around 1500 and then using hand manually choking off the engine until right before it dies to dislodge stuff that may be in the carb. did that a couple times and its no better

ideas?

 

Your fuel pump is not the issue. 4psi is okay. It is determined (and maintained) by the spring pressure under the fuel diapragm, not spacers or engine rpm. Those will affect volume, not pressure.
Carter YF carb needs about 2.5 psi minimum.

I can't see where you tested the vacuum side of the pump...?
But if you can get 19" of vacuum at the manifold, yet it still won't idle with the port plugged, I suspect the problem is elsewhere than the vacuum pump.

Maybe time for a carb rebuild? Possibly the accelerator pump curcuit is leaking?
Checked your sparkplugs for color?

 

1. Upon acceleration intake manifold vacuum will drop to near zero and then recover. That’s why vacuum wipers slow to a stop going up a hill and wipe like crazy when you’re coasting. Inspect the vacuum feeds to your wipers, if they aren’t electric.
2. With the F-134, WIP, do you have the standard PCV set up? PCV on the lower valve cover, a tube to the front. A ’T’ connecting the line to the vacuum pump and then around and up to the intake manifold.
3. Carb cleaner is not volatile enough to give you a clear clue as to the location of a vacuum leak. Use short bursts of starting fluid spray (ether). I use it in diagnosing vacuum leaks myself. Spray it at the throttle shaft where it goes in and where it comes out. This where a carb usually starts leaking air in. Do you have to use choke to idle?
4. The only vacuum line that connects to the throttle base of a carburetor is for the vacuum advance distributor. Engine vacuum needs to be measured at the port where the PCV tube enters the intake.

 

x2

If you tested the vacuum at the carb, you were getting "ported" vacuum and not the true manifold vacuum. And you should test with the PCV line (and all others) disconnected/blocked.

 

I have the original pcv setup like you described.

I measured the vacuum at the hole in the manifold below the carb, NOT the carb itself.

Yes I have to use choke to idle. But I am thinking that's because it also opens the throttle a little. Maybe at that slightly higher idle it runs off a different circuit in the carb and that's why it then works.

Maybe I have such low vacuum trying to idle because maybe a passage in the carb is plugged so it's constantly trying to die making my idle vacuum low?

I will pull and replace spark plugs tonight if I get the time

 

You have 19 inches at a steady throttle setting (holding with your foot) at anything higher than 1500 rpms. That is good. If it is a steady reading at a steady throttle position.

No idle with the line to the pcv disconnected and plugged (having the gauge there is the same thing).

Did someone monkey with the idle speed screw? Or the idle mixture screw? Timing get changed? Is your filter rated for E-10 fuel?

Nothing wrong with your pump - it pushes 4psi and holds that after the engine is shut off.

Could be Varnish in the idle circuit, or even possibly the float has sunk.

 

I THINK that its now fixed.

I removed the top of the carb to check for debris inside and see how things look. it was really clean with only a little very tiny debris trapped in the float bowl. I blew out the jets I could see with top removed from carb and removed the float and sank it in water watching for air to leak out of it since It was obviously not full of any fuel. no problems found. I put it back together and it still wasn't idling right.

then stupid me I checked the idle speed on my tach dwell meter and it looked like it was idling poorly at about 400 rpm so I pulled hand throttle to get rpms up a little while I turned up the idle speed and I got it right around 650 rpm now and it idles much better now and I have about 21.5 inches vacuum at idle and dwell is around 35 degrees. the rpm hunts a little but I will fine tune tomorrow

thanks everyone for the help