carbon build up ---> exhaust port

roadent$ craig / i spotted some pretty hefty carbon build up in my exhaust port on my batavus.

i turned the engine over and i can see the piston moving up and down (cool!) there a safe way to remove the build up with out chunks falling into the cylinder and wrecking the engine...or do i have to take the whole cylinder off and scrape it out?

i feel this could give me more power so i want to do it pretty bad but i dont feel comfortable venturing in the unknown of cylinder work.

Re: carbon build up ---> exhaust port

its best to take off the cylinder... you can do a much more thorough job, use some carb cleaner to help break down the carbon and scrape it out with a screw driver. Be careful not to burr the edges or the exhaust port IN the cylinder, you can always chamfer them down if you do....

Oh yeah, and start using better 2stroke oil!!!


Re: carbon build up ---> exhaust port

i didnt want to tell him to do it .. glad you did because it is the only right way to do the job..

now you gotta tell him how to reinstall the cylinder without breaking the rings..

Re: carbon build up ---> exhaust port

Jason Luther /

take it apart, its very easy and having mopeds youll have to do it often

Re: carbon build up ---> exhaust port

roadent$ craig /

how do i reinstall the cylinder without breaking the rings? thats scary...ill just leave it as it is...i cleaned the muffler out really good anyways

Re: carbon build up ---> exhaust port

it aint that bad.. all you gotta do is be sure the ring's ends do not pass by a port (hole in the cylinder).

This means you align and hold the cylinder steady, and lower it straight onto the piston without turning the cylinder.

Otherwise a ring's ends will spring out and can get caught in a port. Push and bingo.. snapped ring.

The rings have little keeper pins on their ends to prevent the rings from moving around the piston.

Hold the top ring properly in it's groove, lower the cylinder over it .. then hold the next ring and do likewise.

Hardest part is doing all this is most people got only two hands and it's gotta be done in the restricted little space between the cylinder and crankcase. But do it once and it's a piece of cake (not really)


a large amount of carbon in the exhaust port almost guarantees there's carbon built up in the ring's grooves.

if so, they don't seal well .. might even be stuck and unable to move at all. That kills power .. in bad cases it allows hot plasma to shoot past the rings, burning the lubricating oil coating off the cylinder wall.

if interested, ask how to go about removing and reinstalling rings, and how to clean their grooves.. You might get a clue to ring groove condition with a close look into the exhaust port.

or just try to forget i mentioned it.


roadent$ craig /

it doenst run thhhhhaaaaat bad...just the acceleration is slow..other than that it runs ok...i dont think anything too serious is wrong.

Re: btw..


well if it was me id take top end off and clean eerything and reinstall it well thats what i do to every ped i get and tomos mopeds are easy to do i can do it with no eyes lol not really

Re: carbon build up ---> exhaust port

wuts the carbon look like?

Re: carbon build up ---> exhaust port

carbon in the ring grooves? it's like an epoxy-hard black crust that's stuck on there about as good as epoxy too..

Rings need some clearance above them in the groove. This allows very high combustion pressure to get around and behind a ring and so push it against the cylinder wall. Combustion pressure provides the sealing force.

If the groove is packed full of carbon, gas pressure can't get behind them and the rings won't seal.

Re: carbon build up ---> exhaust port

not the rings....but im guessing its the same as the exhaust and the exhaust big much of an effect would an amount of carbon about the size of 2 pennis on my exhaust port and more than 2 quarters in my exhaust have on my power and top speed? joew, can u check my post? i'll bump it just above this

Re: carbon build up ---> exhaust port

ok im gonn sound like a complete idiot. i dont know that much about mopeds, but what is carbon, or carbon build up?

Re: carbon build up ---> exhaust port

carbon is just like coal .. coal is partially burnt wood.. burned without enough oxygen to burn it completely. The left-over is hard black coal.

Partially burned oil does the same thing. Since a two-stroke engine has oil mixed in with the fuel, wherever the exhaust gases go, carbon can build up. It's normal and requires periodic removal.

Exhaust ports, mufflers, ring grooves as well as the combustion chamber surfaces, including the piston crown, can collect carbon.

Re: carbon build up ---> exhaust port

how do u clean it, just take it apart n blow it out?

Re: carbon build up ---> exhaust port

it's stuck on there pretty good.

I like to pick it off carefully with sharp little tools so as not to scratch soft aluminum surfaces, especially not the ring grooves.

Takes a while and requires patience. Magnification and bright light helps.

It can be good therapy after an otherwise hectic day.

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