Finding an internal vacuum leak

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gliderider06

gliderider06

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So, I have a new, stock rebuilt 318 in my ramcharger. Cast spreadbore intake, holley 650. Stock roller cam motor. Has <700 miles since rebuild.
Drove to work great week. Started up to leave just fine. Pulled off post and started sputtering. Low speed surging and missing. Thought I blew a power valve. So, I order a new one (2 stage PV) I install it a week later and it still has same problems. If I close the choke off 1/2-3/4 it runs smooth and happy. Oh, and this is a new 650 spreadbore carb too. I thought maybe I sucked up a piece of dirt in the carb. Anyway, I have an older holley 4011 that I rebuilt and put it on. Ran great until it got warm and started acting up, but not as bad as the other carb. No real change when I close the choke off until its completely closed then it stalls.
But what has me wondering is that it was 1-1/2 quarts low on oil. Within the last 500 miles. It doesn't seem to be burning oil. All plugs look the same, none oily or discolored different from another. Just has me wondering if I should look into something that maybe an intake gasket may be sucking internally or I'm just overthinking it.
Thanks
 
Could even be a cracked intake and we had one member on here been there done that. About all I know is to eliminate what you can externally and be sure of that, and then pull the intake / try another one.

Has anything been milled? Port mismatch? You using "non metallic" intake gaskets? I hated those things.
 
67Dart273 said:
Could even be a cracked intake and we had one member on here been there done that. About all I know is to eliminate what you can externally and be sure of that, and then pull the intake / try another one.

Has anything been milled? Port mismatch? You using "non metallic" intake gaskets? I hated those things.
Click to expand...
Has not been milled at all and using the steel intake gaskets with a light skim of permatex ultra grey around the ports. I cant find any leaks by spraying carb cleaner anywhere when it runs. No signs of burning oil. I cant smell any oil at the tailpipes with it running. I dunno. Just a bit baffled.
Thanks
 
Just went thru the same thing- rebuilt stock 318. I could not control the idle. It was sucking oil thru the ports due to the 318 Felpro gasket set gave me 360 ports. Now I had my 318 heads shaved 0.040” but intake was aligned. (Ld340 with FI fuel injection)
I was sucking 2quarts per 100 miles. Run great and I had about 1000 miles on engine after proper break in. Compression was perfect and leak down was perfect. Called summit and ordered specific 273/318 port gaskets- fixed my issues. Hope yours is as easy.
 
Get a 3 ft piece of vacuum hose stick one end in your ear and run the other other end around the intake, under the intake. I have found more vacuum leaks that way. If you have a vacuum leak you will find it.
 
we used to spray the intake with WD-40 while the engine was running. Find the vaccume Leak every time.
 
gliderider06 said:
Has not been milled at all and using the steel intake gaskets with a light skim of permatex ultra grey around the ports. I cant find any leaks by spraying carb cleaner anywhere when it runs. No signs of burning oil. I cant smell any oil at the tailpipes with it running. I dunno. Just a bit baffled.
Thanks
Click to expand...

If spraying carb cleaner had no effect, the leak may be internal to the engine/intake including the above mentioned potential crack in the intake.

The top portion of the intake face can seal well, while the bottom part of the intake can suck air and oil from the valley pan area. Hughes Engines has a video of this issue and the way they measure for the condition using a crushable, cord-type filament.

Consider pulling off the intake and inspecting the
bottom of the ports for signs of improper sealing. Also, look to see if the bottom of your current metal intake gasket is equally crushed on top and bottom. Try a non-metallic intake gasket that is slighty thicker and more compressible along with an additional film of Permatex Ultra Seal.

Shine a flashlight down the intake ports and see if your intake seals are passing excessive oil while you have the intake off.
 
Thank you all for the responses. I've been Dickering around this truck all day, until now. I put a 4011, 650 holley on it and I just wasnt quite happy with it. Fitment issues with EGR and linkage. So I took apart the new 650 that was on it that was sputtering etc... everything clean as it should be for a new carb. I changed all gaskets, new PV and install it. Still has the same issue. I decided to pull the front bowl off and metering block. I changed out the 2 stage PV, for a good ole' standard 9.5 PV. Crank it over and fired off and runs like a swiss clock. That was 2, of the fancy expensive 2 stage pv's acting up causing my ramcharger to act up.
As far as the intake leaking, not sure. Inside the intake clean and oil free. It's due really soon for its next oil change. Maybe I'll start with that, closely monitor the oil level a d order new intake gaskets in the meantime. I do have an Eddy Performer EGR intake I can put on to replace the cast iron one.
Thanks all!
 
gliderider06 said:
So, I have a new, stock rebuilt 318 in my ramcharger. Cast spreadbore intake, holley 650. Stock roller cam motor. Has <700 miles since rebuild.
Drove to work great week. Started up to leave just fine. Pulled off post and started sputtering. Low speed surging and missing. Thought I blew a power valve. So, I order a new one (2 stage PV) I install it a week later and it still has same problems. If I close the choke off 1/2-3/4 it runs smooth and happy. Oh, and this is a new 650 spreadbore carb too. I thought maybe I sucked up a piece of dirt in the carb. Anyway, I have an older holley 4011 that I rebuilt and put it on. Ran great until it got warm and started acting up, but not as bad as the other carb. No real change when I close the choke off until its completely closed then it stalls.
But what has me wondering is that it was 1-1/2 quarts low on oil. Within the last 500 miles. It doesn't seem to be burning oil. All plugs look the same, none oily or discolored different from another. Just has me wondering if I should look into something that maybe an intake gasket may be sucking internally or I'm just overthinking it.
Thanks
Click to expand...
Most likely the wrong intake gaskets sucking both oil and air from inside the valley.
That's why you have to run it with some choke it is super lean from the air leak.
 
I assume you've checked the common culprits on vacuum leaks? PCV hose, brake booster and hose, other vacuum hoses?
 
This test is too easy; put a vacuum gauge on the dipstick tube, then flip the PCV out of the valve cover but leave it attached at the carb, Remove the breather and plug all holes into the calve covers and CC.
Finally start it up and increase the idle rpm to at least 1200 to 1500 while watching the gauge.
There should not be any vacuum there now.
There should be a pressure building up in there which you must not allow to got past about 3 psi., or it could push your rear cam plug out.
 
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