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1980 XL 500 S : Problem-- referral if possible

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Greetings:

I have a mint 1980 XL 500 S that radiates a cracking popping sound similar to walking on gravel, once warmed. Specifically,noise is coming from the exhaust valves (as if the oil is boiling).

The intake manifold and insulator have been checked for cracks.The Orings at this location have been replaced with Viton items.The carb has been tanked and sealed top to bottom. New copper exhaust port Orings have been installed. A new plug was installed, B8E. Compression is within normal spec.

There is no smoke on start,idle or rev. The plug is running on the rich side as .75 mm shim has been installed to correct for California fuel at sea level ( Coastal So Cal elevation).

The petcock has been tanked and air blown. Floats are at factory spec. The filter is an after market foam unit. The air box has been silicon sealed and clamped correctly. The valves are set to mid range spec. The mechanical timing advance is intact and working.

Bike starts on 2nd or 3rd kick.

Normally, the audible sound describe above is resultant of an air leak in the intake manifold due to faulty O-rings or broken insulator. All this has been accounted for.

What is left to account for? What is the fix?

thanks

H2

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Hey Eddie

The exhaust is not popping and there is no mechanical sound.

Its a crunching/ popping sound that starts once the motor warms up and persists when the motor stops. The sound is definitely coming from the exhaust cam / valve area. The sound slowly dies out, presumably from the area cooling off. There is no debris when the oil is drained.

Could this be a result in a crack in the head at the exhaust valve / seat? BTW the plug looks OK on inspect but the silver paint in the exhaust area is discoloring (when it normally does not)

thanks

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Yeah, I paint all my engines silver so I can see leaks or hot spots on the engine. The paint bakes on and is viable to 450 degrees. An air leak at any spot will show discoloring / browning paint.

This engine is showing discoloring at the exhaust valve area.

My other bikes show no discoloring.

So what sayest thou to my query?

H2

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