Mazda Zoom Power engine cleaner works wonders.
Step one is to warm up the engine,
Step two, disable fuel and spark, (disable spark by unpluging the Crank angle sensor)
Step three, remove a single rubber nipple ( Insert joke here) From the lower intake manifold, take Mazda Zoom power engine cleaner with extension hose inserted into port opening.
Step four with the assistance of a friend, have your friend hold the throttle wide open and crank the engine ( While the engine is still hot mind you) and spray cleaner into port, Spray cleaner for roughly ten seconds. After ten seconds, wait for thirty seconds, then repeat once more.
Step five, repeat step three and step four on rear port.
Step six, allow cleaner to sit in vehicle for an hour or so, be patient.
Step seven, re-enable fuel and spark.
Step Eight, crank engine and wait until it starts. ( This sucker is going to smoke badly for a few moments depending on the level of carbon build-up if any at all.) If the engine won't restart due to flooding, just disable fuel again and do a typical de-flood procedure on it
This should remove carbon build-up well enough. But I agree with Aaron Cake though, this is only as a last resort, the next step would be a proper rebuild.
I've used this stuff on my personal car and on Rx8's and it's brought back a few engines ( Including the one currently in my Fc) You can get it from your local Mazda dealer for roughly 35 bucks.
Anyway, good luck.
Last edited by Jdrift; 06-14-11 at 06:08 AM.