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Best way to check for vac leaks?

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Old Oct 10, 2011 | 04:23 PM
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G. Man's Avatar
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Default Best way to check for vac leaks?

Ok, So my car is running extremely lean. The mechanic said about 10x to lean. What can I do to figure this out. With the air cleaner off, I spray carb cleaner around the base of the carb and the idle speeds up. Doesn't do it anywhere else, so I'm thinking it's the carb gasket. But I was also thinking that some of the carb cleaner could be evaporating up and getting in, causing this. I want to have the carburetor rebuilt anyways, but I don't want to spend the money without knowing why it's running so lean or where this vac leak is.
Any suggestions will be appreciated.

Oh, I don't think it's a vac line causing this. I've replaced quite a few, and the others look good.
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Old Oct 10, 2011 | 07:28 PM
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92dxbeast's Avatar
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Default Re: Best way to check for vac leaks?

Try taking the whole carb off and clean it
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Old Oct 10, 2011 | 08:06 PM
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Default Re: Best way to check for vac leaks?

Before you do that, put the air cleaner back on and spray the base with the carb cleaner. If the idle still bumps up, then you KNOW it's the carb spacer. Last I checked (last week for a co-worker), they were like $75-$90 from Honda.
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Old Oct 10, 2011 | 08:36 PM
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Default Re: Best way to check for vac leaks?

Another good way to test for vac leaks is to use WD-40... if the oil hits a leak, you will notice it run differently for around 20 seconds before the leak opens up again. I used this trick all the time on my spaghetti pile of nightmare vac hoses.
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Old Oct 11, 2011 | 04:58 AM
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Default Re: Best way to check for vac leaks?

First off, thanks for the reply's everyone.

Originally Posted by Gustav129
Before you do that, put the air cleaner back on and spray the base with the carb cleaner. If the idle still bumps up, then you KNOW it's the carb spacer. Last I checked (last week for a co-worker), they were like $75-$90 from Honda.
I did try with the air cleaner on, but there are a couple slits on the bottom of the air cleaner where the carb cleaner gets in, and speeds up the idle. I first thought I had a gasket leak on the intake manifold, because when I sprayed around it I got the idle to increase. But then I realized there were those slits on the underside of the air cleaner (factory slits about a 1/4 inch long, not cracks or anything that's not suppose to be there).

Is there just the carb spacer there, or is there a gasket too? Or is the carb spacer a gasket lol?
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Old Oct 11, 2011 | 08:41 AM
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Default Re: Best way to check for vac leaks?

I had an issue with my caddy where I couldn't be 100% certain with carb cleaner.
Maybe i'm too deaf or just suck at it.

So I bought a pvc cap and a rubber coupling that were about the size of the MAF sensor.
Drilled a hole and screwed an air nipple into the cap, then capped off the MAF.

With my air compressor regulator backed off to less than 2 psi I could take my time and spray soapy water all around and located every leak visually.

It cost like $5 and should work just fine on your carb as well.
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Old Oct 11, 2011 | 10:20 AM
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Default Re: Best way to check for vac leaks?

We just had a big discussion about this. Or maybe it was on a Mustang forum.

You don't want to be looking for a VACUUM leak by pressurizing the system.

A vacuum leak can be caused by a simple internal diagonal cut on a vacuum hose, and the hose is porous enough to leak vacuum. If you pressurize the system, that flap can be held closed and no sign of a leak present.
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Old Oct 11, 2011 | 10:21 AM
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From: Near the race track....
Default Re: Best way to check for vac leaks?

We just had a big discussion about this. Or maybe it was on a Mustang forum.

You don't want to be looking for a VACUUM leak by pressurizing the system.

A vacuum leak can be caused by a simple internal diagonal cut on a vacuum hose, and the hose is porous enough to leak vacuum. If you pressurize the system, that flap can be held closed and no sign of a leak present.
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Old Oct 14, 2011 | 04:23 PM
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From: Idaho
Default Re: Best way to check for vac leaks?

Originally Posted by G. Man
First off, thanks for the reply's everyone.



I did try with the air cleaner on, but there are a couple slits on the bottom of the air cleaner where the carb cleaner gets in, and speeds up the idle. I first thought I had a gasket leak on the intake manifold, because when I sprayed around it I got the idle to increase. But then I realized there were those slits on the underside of the air cleaner (factory slits about a 1/4 inch long, not cracks or anything that's not suppose to be there).

Is there just the carb spacer there, or is there a gasket too? Or is the carb spacer a gasket lol?
BUMP!
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Old Oct 16, 2011 | 10:51 AM
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From: SF bay area
Default Re: Best way to check for vac leaks?

Originally Posted by G. Man
I did try with the air cleaner on, but there are a couple slits on the bottom of the air cleaner where the carb cleaner gets in, and speeds up the idle. I first thought I had a gasket leak on the intake manifold, because when I sprayed around it I got the idle to increase. But then I realized there were those slits on the underside of the air cleaner (factory slits about a 1/4 inch long, not cracks or anything that's not suppose to be there).

Is there just the carb spacer there, or is there a gasket too? Or is the carb spacer a gasket lol?
The vacuum system is a marvel of Rube Goldberg machinery. There is colored schematic on picasa when I tried to find my leak(s) on the EW1 engine for the 86. I stopped chasing it until it gets worse. I have another 16 months until the next smog check.

What I have noticed is the first morning start the engine will go above 3000 rpm for a 15 seconds after I drive, there is something to track. I run lean too at 1500ppm of Nox.

I played with the air filter and plugged the disconnected hoses to prevent vacuum leaks, I tried to bypass some system to isolate a possible malfunction.... I have 2 units to work on, the cold advance is non op, and the anti back fire valve.

As for carb gasket there is a gasket.

Best,
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