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Hi All,

I was changing out the rear tire so I had to take off the muffler. So when I was putting it back on, I noticed that a valve was coated in some white stuff. Any ideas as to what it might be?

Mike
 

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Are you saying you looked up inside the exhaust port on the head and saw white deposits on the exhaust valves?
 

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Exhaust valves generally are white / cream coloured on their trumpet shaped rear. Its the inlet valves that generally get covered in black crusty carbon deposits from the fuel mixture etc.

Well that's what I have found over the years, providing the engine is running well.
 

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It's ash residue from the pair system's injecting of fresh air into the exhaust port to burn up any unburned hydrocarbons in the exhaust gas. It is common on engines with secondary air injection systems, though not many are still using that technology.



Get rid of the PAIR solenoid control valve and, plug the ports at the air box and PAIR reed valve, and it will stop building up--and even go away a bit. The headpipe and exhaust port/valves will run cooler too...
 

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Exhaust valves generally are white / cream coloured on their trumpet shaped rear. Its the inlet valves that generally get covered in black crusty carbon deposits from the fuel mixture etc.

Well that's what I have found over the years, providing the engine is running well.
That is right Gio. LIght brown to white ash deposits on exhaust valves are kind of normal. That is why I ask him for a clarification on what he was seeing.

What you don't want to see is black deposits on the exhaust valves. That indicates the engine is burning excessive amounts of oil.
 

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But doesn't that deposit show up on the exhaust manifold and not the valve as the poster mentioned ?

Edit this is in reply to cliffyk by the way. :)
 

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What would be the best thing to do then? Just take off the pair solenoid and take away the pair reed valves too? Does that help it or something? This is what I was looking for on here before. Of course it shows up after its all back together. Lol
 

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What would be the best thing to do then? Just take off the pair solenoid and take away the pair reed valves too? Does that help it or something? This is what I was looking for on here before. Of course it shows up after its all back together. Lol
The "best" thing to do would be to not worry about it, because as others have said some white/cream color deposits on the "back" of the exhaust valve are normal--secondary air injection systems exacerbate the condition.

In the late 60s and 70s "smog pumps" were the common response to more strict emissions requirements, and the startling build up of ash in exhaust ports and on valves was equally common.

As to removing the pair solenoid and blocking the airbox and reed valve ports, I have discussed that in detail in other threads where you have participated and do not care to rehash it here.

But doesn't that deposit show up on the exhaust manifold and not the valve as the poster mentioned ?
Yes, and on the back of the valve--the air is injected into the exhaust port and the "external" combustion is not confined to downstream only. Exhaust valve fouling/leaking/burning was a major issue in the smog pump days, one of the reasons the US automakers got such a bad reputation.

The japanese put some real research into making engines more efficient so that silly afterburner emission control devices were not needed--the US makers just made them run lean and dropped the HP down to absurd levels--like the whopping 145 to 160 HP from the 350 V8's in the mid-70s Camaros...
 
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