[Rich Biebel]

The Onan brand, 4 C cleaner is a good product but it will never clean the carbon as well as I do when I do one of these machines. Removing the heads is the only way to really get the job done properly. It is a recommended service by Onan every 500 hours. Doesn't have to be done that often but will need that service at some point in it's life.

The carbon buildup is very bad on these units and especially on the rear cylinder. Removing the heads.....clean them to like new and I also do the pistons and the valves and seats. The backs of the intake valves will have heavy carbon deposits.

They can get so bad the engine will not turn over! Every time you shut it down the remaining fuel solidifys and builds up on one side of the piston due to it being a horizontal engine......The carbon piles up so high it will stop the engine from turning over and that is also the carbon knock you hear.

We ( me and Matt Schurman) removed one of these units from a Salvation Army canteen vehicle at the World Trade Center site just after 9/11......and that one was the first time I saw one so bad it would not turn over.....I fixed it up and it ran for years after that....