Every other exhaust valve is white

[Mr Lee]

So I went to replace my leaky exhaust manifold gasket and while I had the manifold off, I noticed that cylinders 1 and 5 had white exhaust valves.  3 and 7 looked fine.
(I didn't get a pic of #7) 
Spark plugs looked fine.  No oil on them or anything.  What does this mean?  Why would there be such a noticeable difference? 
2k miles on rebuilt engine (383).

[Cudajason]

So I went to replace my leaky exhaust manifold gasket and while I had the manifold off, I noticed that cylinders 1 and 5 had white exhaust valves.  3 and 7 looked fine.
(I didn't get a pic of #7) 
Spark plugs looked fine.  No oil on them or anything.  What does this mean?  Why would there be such a noticeable difference? 
2k miles on rebuilt engine (383).

what intake manifold are you running?

[Mr Lee]

@Cudajason

Running the stock cast iron one.  But I have an Edelbrock Performer I am going to put on soon.

[MoparLeo]

Lean. Possible intake leak. How hot did the engine run ?

[Mr Lee]

Lean. Possible intake leak. How hot did the engine run ?

The temp gauge has always been normal.  It's never run hot that I've noticed.

Last year with a different carb, my spark plugs looked very different from each other.  The ones in the front of the engine were normal and the ones in the back were rich.  I did a vacuum leak test and it was good.  But I redid the valley pan gasket and intake gasket just to be safe. 

Now the plugs all look similar but the valves don't.    ..No idea. 

I put a new carb on recently but it's been running pretty strong.  Just working out a hesitation here and there.  Just carb tuning.  Shrug.

[RzeroB]

The right (even) bank follows the same pattern?? I wonder if you follow the intake runners from the heads to the plenum if they would all be on the same side?? If they are, maybe one side of your carb is lean??

[Mr Lee]

The right (even) bank follows the same pattern?? I wonder if you follow the intake runners from the heads to the plenum if they would all be on the same side?? If they are, maybe one side of your carb is lean??

Hmmm interesting theory.  I didn't check the right side but maybe I will. 
But wouldn't the plugs read lean on those cylinders also?


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[dodj]

My first thought was you have a dual plane intake, and a carb that has issues on one side.
In line with Tom's thinking. 

[Filthy Filbert]

I agree.  Classic indication that one half of a dual plane intake is running lean for some reason.   plugged jet, intake manifold gasket leak, etc. 

I had the same exact symptoms when I took my 383 out of the blues cuda.   Only my issue was a leaky brake booster diaphragm that caused half the intake to go lean.   I also had 2 burnt exhaust valves; so you should find out why you're lean and get it fixed asap.

[Mr Lee]

I agree.  Classic indication that one half of a dual plane intake is running lean for some reason.   plugged jet, intake manifold gasket leak, etc. 

I had the same exact symptoms when I took my 383 out of the blues cuda.   Only my issue was a leaky brake booster diaphragm that caused half the intake to go lean.   I also had 2 burnt exhaust valves; so you should find out why you're lean and get it fixed asap.

Interesting!  Thanks for the info.

I have experienced my brakes sometimes dragging slightly when i roll to a stop (manual trans).  On a slight grade when i should be rolling while in neutral, i wasn't.    My temporary repair for this was to install a spring that pulls the brake pedal up that last little bit.   So would this indicate a leaky brake booster?    Or does that just indicate that too much suction is pulling the diaphragm.  And if so, why?   I mean, wouldnt a leak cause less brake assist instead of too much?   


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[70 Top Banana]

I agree, looks like the carb is running lean.

[Mr Lee]

Thank you all for the input but this remains a mystery.

I have an air/fuel ratio gauge with 02 sensor in the drivers side exhaust pipe and I am on the rich side, running ins the 13's mostly (with an ideal ratio of 14.7 parts oxygen to 1 part fuel, ...the 13's would mean less air to fuel ratio which would be rich).

Regarding the brake booster, the booster plugs into the #7 cylinder intake runner.  The exhaust valves that are white are # 1 and 5, so that theory doesn't really line up or else I think cylinder #7 would be white.   I also did several tests on my brake booster and there is no vacuum leak. 

I also performed a vacuum leak test spraying some brake cleaner around the intake and carb and did not find one.

Another thing that remains a mystery is that my spark plugs look totally fine.  I don't understand how the exhaust valve could be totally white and the plug read normal?  Typically we read the plugs to see if we're lean or rich.  If I hadn't seen the exhaust valves I would never have known there was a problem.

I got these pics from the internet of a 383 intake.  It looks like the the passenger side of the carb feeds cylinders 3 and 5.  The drivers side feeds 1 and 7.  Yet my valves that are lean / white are 1 and 5.  So I don't see how one side of the carb could be causing this. 

I guess the next thing I should do is pull the passenger side exhaust manifold and check those valves. 
I also have an Edelbrock intake that I am going to put on. 

Any other suggestions would be welcome.  Thanks.

[ek3]

ONLY EXHAUST ...  sucking air back in... at the exhaust manifold ?