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Vacuum Leak - Can't Find It

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Old 02-16-2017, 11:58 AM   #61
rahaul
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Has a basic compression test been done on this engine? It would tell you if the rings are still healthy so you can rule that out.
Yes, one of the first things I did. All from 180 to 200.
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Old 02-16-2017, 08:48 PM   #62
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Rings are good look elsewhere for the leak.
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Old 02-19-2017, 07:15 AM   #63
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Rings are good look elsewhere for the leak.
There are two things that come to mind that may or may not be related to the "must be a vacuum leak" diagnosis and was not a problem until recently:
1. the plugs are oil fouling like never before. There even is oil on the threads. I rarely see any oil smoke from exhaust.

2. The exhaust at idle is so rich it will burn your eyes big time. I first thought this a carb problem but after swapping out 3 other carbs (1 new and 2 new rebuilds) I have to deduct there is something else here.
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Old 02-19-2017, 08:59 AM   #64
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There are two things that come to mind that may or may not be related to the "must be a vacuum leak" diagnosis and was not a problem until recently:
1. the plugs are oil fouling like never before. There even is oil on the threads. I rarely see any oil smoke from exhaust.

2. The exhaust at idle is so rich it will burn your eyes big time. I first thought this a carb problem but after swapping out 3 other carbs (1 new and 2 new rebuilds) I have to deduct there is something else here.
In reference to item 2, not necessarily. I went thru the same with 4 carbs. It seems the carbs from the builders are all set up on the rich side and you have to lean them out.
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Old 02-19-2017, 01:41 PM   #65
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Based on your first removal of the intake and finding all the oil in the ports and a wet gasket I think you found your problem but it did not get fixed.
You might be able to run a camera wand down the carb and inspect those intake ports again to see if the intake ports are oiled up again.
If it was mine I would pull that intake, put a straight edge on it and really closely inspect the gasket. It will have a crush area showing where the intake was torqued and maybe where there was no torque due to warp or other issues. Make sure the gasket you use is designed to seal cast iron block with aluminum heads. Aluminum moves a lot more than cast iron and the gasket needs to be able to allow for this slip or movement.
Many guys have switched to thicker intake gaskets to solve minor manifold imperfections.
Might inspect that intake for cracks on the bottom/oil side.
Bad valve stem seals could certainly leak oil into the combustion chamber but would not affect your intake gasket seal or put any oil at the top of the intake runners.
Oil at the top of the runners is coming down and is not from stem seals.
Have you run this engine with the PVC disconnected? Any chance it is open and pulling air and oil into the intake, big intake vacuum leak and it pulls oil if bad.
Just random thoughts on your issue, hope we strike gold with one.
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Old 05-10-2017, 08:24 AM   #66
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Quote:
Originally Posted by Westlotorn View Post
Based on your first removal of the intake and finding all the oil in the ports and a wet gasket I think you found your problem but it did not get fixed.
You might be able to run a camera wand down the carb and inspect those intake ports again to see if the intake ports are oiled up again.
If it was mine I would pull that intake, put a straight edge on it and really closely inspect the gasket. It will have a crush area showing where the intake was torqued and maybe where there was no torque due to warp or other issues. Make sure the gasket you use is designed to seal cast iron block with aluminum heads. Aluminum moves a lot more than cast iron and the gasket needs to be able to allow for this slip or movement.
Many guys have switched to thicker intake gaskets to solve minor manifold imperfections.
Might inspect that intake for cracks on the bottom/oil side.
Bad valve stem seals could certainly leak oil into the combustion chamber but would not affect your intake gasket seal or put any oil at the top of the intake runners.
Oil at the top of the runners is coming down and is not from stem seals.
Have you run this engine with the PVC disconnected? Any chance it is open and pulling air and oil into the intake, big intake vacuum leak and it pulls oil if bad.
Just random thoughts on your issue, hope we strike gold with one.
I had to set this aside for a while to mentally regroup. Appreciate everybody's help and input. I also now have a friend, Matt, who works at a local shop on this dilemma. Matt spent 2 hr on it recently. He's going over some basics and is not convinced it is a vacuum leak we are dealing with. He found that all the ports on the QJet had 13" vacuum. He was thinking the vacuum advance port should only have 2"-3". I swapped QJets and this one also has 13" on the vac advance port.

So how much vacuum should this port have at idle?
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Old 05-10-2017, 11:42 AM   #67
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I chased a vacuum leak on my 65 350hp car and it turned out to be sucking from under the intake at the lower area of the runners. New set of intake gaskets fixed the problem.
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Old 05-10-2017, 01:31 PM   #68
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I chased a vacuum leak on my 65 350hp car and it turned out to be sucking from under the intake at the lower area of the runners. New set of intake gaskets fixed the problem.
I replaced the intake gaskets and was thoroughly convinced it would fix the problem. Actually it fixed another problem that had developed in the midst of the vacuum leak problem which was the plugs were oiled like never before. For some weird reason the intake gaskets were not sealed to either head nor intake and they were oil coated. If pulled and reset this intake more times than I can count since 1986 and that has never happened. It is a GM alum intake. Since the new gaskets were put on the oil wet plugs have dried up.

So what were your vacuum leak symptoms?
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Old 05-11-2017, 10:38 AM   #69
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I just had a tuning problem on my 1963 L76, that looked a lot like yours, and left me scratching my head. After help from the forum, I replaced my PCV valve, and it corrected what looked like a huge vacuum leak, or a carb issue. The PCV rattled, but it wasn't functioning. I had a too strong vacuum from the inlet on the ventilation system, and it was drawing in lots of unmetered air and screwing things up. On my 1963 L76 the PCV is restrictive. Not sure what your system is, or how it's plumbed, but it should be easy to check. My vent system inlet air came from the oil file tube, and the vacuum there was extreme, when it should have been just enough to draw in a piece of paper. I never thought that a PCV would create such a problem; but in my case it did.
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Old 05-11-2017, 01:33 PM   #70
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I just had a tuning problem on my 1963 L76, that looked a lot like yours, and left me scratching my head. After help from the forum, I replaced my PCV valve, and it corrected what looked like a huge vacuum leak, or a carb issue. The PCV rattled, but it wasn't functioning. I had a too strong vacuum from the inlet on the ventilation system, and it was drawing in lots of unmetered air and screwing things up. On my 1963 L76 the PCV is restrictive. Not sure what your system is, or how it's plumbed, but it should be easy to check. My vent system inlet air came from the oil file tube, and the vacuum there was extreme, when it should have been just enough to draw in a piece of paper. I never thought that a PCV would create such a problem; but in my case it did.
I did replace the PCV valve. The old one also rattled but I never did check the volume of air either before or after. I can see why it would screw things up if unmetered. Thanks.
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