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Old 09-15-2013, 08:19 PM
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Vacuum Leak

Got a 66 283 bored .040 over stock bottom end, 305 heads with Z-28 springs casting # 416,s. The heads were milled .010, with a summit stage 2 intake manifold, edelbrock 500 cfm, msd street fire hei dissy, and a summit #1102 cam 204 214 duration at .50, summit 1 and five eights long tube headers, and 2 and a half inch dual exshaust in my 67 camaro. Timing is 16 deg and 20 mechanical for a total of 36 deg at 2700 rpm. Trying to get carb dialed in and i noticed vacuum gauge fluctuating half deg and idle is not steady. When i changed out cam i noticed the bottom of the intake gaskets were oily. So thought about that and put my hand over the primary's and the engine kept running. so i think that happened again because i find no vacuum leak any where else. Now here is the thing i don't understand. When i pull out the pvc valve from the valve cover the engine runs smooth no vacuum or idle fluctuations. Anyone have a idea what that's about?

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Old 09-15-2013, 11:25 PM
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Yank the carb and look into the intake plenum. If you see any oil in the plenum the intake gaskets are leaking. This could be due to the intake being warped or other issues. If there is no oil in the plenum then yank some spark plugs, if some have oil on them and some don't then there's another indication of intake gasket leaks.
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Old 09-16-2013, 12:18 AM
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There is oil on the plug threads but no sign of it burning oil . I have about 200 miles on engine and has used no oil.
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Old 09-16-2013, 03:44 AM
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Do you have a vent in the other valve cover so the PCV valve has somewhere to draw air from? The carb is sucking air into the carburetor base through the PCV valve and it needs to have air entering through the opposite valve cover.

From what I remember, a fluctuating vacuum gauge indicates possible valve issues. Have you tried readjusting the valves to make sure you don't have one too tight?

Did you use the recommended gaskets on the intake manifold? Most aluminum intakes use a relatively soft gasket so that can compensate for any flex in the manifold. With milled heads this might be even more important, although milled .010 is not that much. When I installed my Edelbrock manifold they had very specific recommendations about which gaskets to use and which to avoid.

Bruce
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Old 09-16-2013, 12:47 PM
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The other valve cover has a breather cap. All the rocker arms were adjusted half turn from zero lash per cam installation instructions. I have been using fel pro gaskets. Per summit instructions i did not use rtv on intake or head side the first time. But when i changed out the cam i did noticed the gaskets were oily on the bottom ends { valley} so i put rtv on the head side this time. I look in the intake plenum and it looks a little brown. So i think it did not seal right. So im going to try and hook up the vacuum gauge to the valve cover like i read on one thread and see if it reads vacuum.
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Old 09-16-2013, 01:28 PM
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Ok i took off breather cap and pvc valve. hooked up vacuum gauge and pluged other hole and got a increase in pressure no vacuum reading. When i hooked up everything it ran smooth and now i got steady 16 in of vacuum. Now if i put my hand over the carb primaries it almost stalls engine. So still thinking the intake gaskets are leaking. any thoughts on this?
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Old 09-16-2013, 01:43 PM
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Quote:
Originally Posted by camaro 67 View Post
All the rocker arms were adjusted half turn from zero lash per cam installation instructions.
How did you find zero lash, by the "twist the pushrod" method or the "jiggle up and down on the pushrod" method? Yes, it matters.
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Old 09-16-2013, 04:07 PM
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up and down movement on the rocker arms
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Old 09-19-2013, 08:47 PM
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i pulled the manifold and foumd oil in # 5,7 and 6,8 runners. cleaned every thing and checked the heads and manfold to see if they are straight and they are fine. The old gaskets showed that these runners were not sealed as good neer the bottom as they should have like #1,3 and 2,4 were. Put everthing back to gether and letting it sit for two days so sealer can dry good. This time i used permatext aviation sealer on both sides of the gasket and of course rtv on front and back of engine block.
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