Ok, this one is baffling. I just pulled both my 525EFI's for some winter work and both, including the one rebuilt last spring have a bit of amber like material in the exhaust ports of the heads. I searched around online and found a few other people with the same thing, but no answers on what it is. Maybe something from the fuel? Anyone have any ideas???

That could be residue from evaporating water . Did you pressure check your headers ?

They are Hardin, and I check them every winter. Plus, it is in almost every cylinder (varying amounts) on both engines. Only thing that makes sense is something in the fuel.

I see said the blind man . Anything laying in the exhaust ports should have passed through the combustion process and hence be exhaust smoke or carbon . My conclusion is the same but i'm just a nobody trying to help you . What do your spark plugs look like ? They usually have a story to tell .

if you can post a pic it would do a lot better then us guessing what it is...

Is it the pink/amber dye from the antifreeze?

The texture is also what throws me. It is soft, like amber, not hard and crumbly like salt.

looks like condensation,,where you located?

i also see white stuff around the end of the valve seat,and looks like a lot of rust on the freeze plug,strange since they are brass when they leave mercury.