Compression Reading. One Cylinder High?

[magnusver4]

Been Struggling with getting my car running right. Decided to replace my spark plugs since I am still trying to track down why my timing mark is jumping occassionally. I figured the plugs are fouled causing the spark to jump to the wrong cylinder.

While I had each spark plug out, I did a compression test on each cylinder (while cold). All cylinders read 150 +/-2 psi, except one cylinder read at 175psi. I tested the high cylinder twice with the same result. What could cause this? Is this considered a problem? My only thought was excessive carbon build up but don't understand the theory behind it. Should this be fixed? I will try and run the test again when the engine is warm. The spark plug was fouled.
Thanks,
Magnus

[UltraMonzas West]

Usually OIL / CARBON buildup! pull the head and clean up....re-assemble and you should be OK...

[Spectre]

Should the "water down the carb" trick be tried before pulling the head?

[magnusver4]

Thanks for the responses!

I bought a can of the GM Engine Top Cleaner but am a little nervous to try it. If I pull the heads do I need to relpace pushrod seals and readjust valves? New Head gaskets, exhuast manifold gaskets?
Thanks

[Spectre]

If you pull the heads, I'd replace all the gaskets/seals.

[UltraMonzas West]

You can try the cleaner....I'm a advocate of the water wash.....but with only ONE cylinder.....must not have been firing for a long time [ I've seen many] the carbon is pretty hard to remove....except by hand...