Lark 8 runs smooth,then gets louder

About the last three times ive ran it[the one in the pic]i noticed it ran smooth as silk and pretty quiet for about an hour.After i shut it down for 10 min or so and start back up the motor is slightly louder but with a lower tone.No power loss,fires back up every time,water pumping good,,,,,,any ideas why the change in the sound of the motor after getting warmed up?

Re: Lark 8 runs smooth,then gets louder

ok,i will answer my own post.one guy said that it sounded like it might be too rich running after warm up,,,,,,,,,but an hour of warm up?i dont know.im still trying to figure it out. runs so good for an hour or so,,,then the rougher,louder sound kicks in

Re: Lark 8 runs smooth,then gets louder

still wondering if anyone has heard of this happening before

Re: Lark 8 runs smooth,then gets louder

39 views,no replies,,surely someone has ran across this prob before.

Re: Lark 8 runs smooth,then gets louder

If you're open to speculation ( guessing) , take the compression when cold then do it again when the sound changes. If the compression readings drop when hot (and running rough) I'd say you are hearing a head leak.
Does it run hot?

It could also be an exh cover plate warping when heated up.
Look for a small access plate with burnt paint on the side of the head.

Another guess, is the engine slowly tilting up ? could be an exh comes out of the water unless it all goes through the prop, if so it could be the exhaust inside the leg leaking (old gasket).

If the compression is good cold and hot and if the engine isn't running too hot, I'd let it ride seeing as it runs ok otherwise.?

Re: Lark 8 runs smooth,then gets louder

yes definitely open for educated guesses.thanks for the info.doesnt run hot..i will do the comp tests cold and hot,, and check the exhaust cover plate.hopeing its something simple.thanks jonesg