So what actualy removes the carbon, water or meth?

Water.

But the addition of meth seems to speed up the process. 

Thanks.

 I am too lazy to set up a full water injection system but I mist water down the inlet every time I change the oil. I usually spray about a litre and the ute is running better every time, I will mix a little meth next time.

I'm setting up a water injection for my lister  engine. 
It will be uber simple, just a drip of water onto the Commodore paper air filter element I'm using.  I have set it up so when , as I inevitably will, forget to turn off the water, the excess will just dribble out the bottom and NOT into the engine. 

I tested it the other week by saturating the filter with water and then starting the engine. Ran fine and of course dried out the element quick and with no damage to the element. 
​The main worry with that is under loading it and on Veg oil

I have been squirting water into the intake with a spray bottle and I can't pump fast enough to make the thing notice. Amazing how much water Diesels can Happily take. 

I think I might have gummed the rings on the old Girl. I did have as I suspected for a while a blocked return line and that was causing massive over fuelling of the engine. That's a bad thing with Veg because the excess " Fuel" carbonises and forms a tarlike crap that sticks up the rings. So far the water doesn't seem to be doing a lot of good in shifting it. I think I let it go too long to be helpful.
I'm thinking of installing a manual switch and running the water nearly full time and seeing if that helps. 

I'm in 2 minds as to whether it will or not but I'll give it a go. Not really worth rebuilding the engine but I don't want to loose the old girl either. 
Even a re-ring and bearing Job will probably be the better part of $2500 so seems I have some decisions to make.  :0(

Try this mate. I have used it in some pretty stuffed motors and they came good. http://www.costeffective.com.au/show_product.php?ItemId=25

 

An old Benz that I used to drive gained a new lease of life until it was sold (40000km later) cos it was a pig to drive. The carbon/glaze was gone and it ran like a dream.