exhaust port carbon build up

Ok, so I took off the cylinder and the head to clean it. The exhaust port was so clogged i'm surprised the ped actually ran. There are also 2 ports on the side of the cylinder (intake?) Which are badly clogged. I tried scraping as much carbon as I could with a plastic butter knife but it didnt seem to do much good. I also tried carburator cleaner but that seemed to take too long. I'm wondering if I should soak it overnight in something to loosen up the carbon?

Any help would be appreciated.



'78 Puch Maxi Sport MKII

Re: exhaust port carbon build up

I usually use a fine grade of steel wool to clean off carbon. Make sure you clean all the little pieces out when you are finished. Metal shavings in an engine are bad.


Re: exhaust port carbon build up

Plastic ??

No plastic... Use a real live (old) butter knife.. like stainless steel.

And just scrape away... scrape... scrape... scrape... scrape.

You don't have to get it perfect or "polished"... just let the air flow.

If the butter knife won't reach in, you will have to use something else metallic

Try not to put scratches in the cylinder finish.

Re: exhaust port carbon build up

Steel wool will take carbon off leaving a shiny metallic surface that looks like new. Without the scratches a butter knife or flat head screwdriver will leave. All it takes is a little elbow grease. I

exhaust PORT carbon build up

I am not arguing with you.... Or saying you are wrong dave.

The guys question was about how to get carbon out of the inside of the exhaust port

And inside the transfer ports.

Not on the head... like you are talking about.

How do you stick a flimsy piece of steel wool inside of a port for any good effect?.

You can't.

And scratches in ports don't hurt anything.

And carbon on the top of the piston and inside the head don't really "hurt" anything, and there will be no performance improvement by getting rid of them.

(in fact... they raise the compression ratio...more HP)

So I really don't worry about them.

I will scrape them off if they are thick and black... cause a piece might flake off.

But getting it all pretty and polished is just to satisfy a need for cleanliness I guess.

And by the way... they are only thick and black when the ped is running too rich (fuel to air). Or the guy was using ordinary motor oil.

My engines are jetted correctly and don't get thick black carbon.

Mine get a light brown thin coat (if any)... ...so I never even worry about it.

Re: exhaust PORT carbon build up

Sorry Fred, your right, using steel wool to clean out the exhaust would polish it, which is bad for a reason I forget. Or maybe it

Re: exhaust PORT carbon build up

Actually ... a lot of moped ports are so small that I don't think a butter knife is even small enough to get in... The guy who asked says his port is almost clogged shut... that is probably going to take a screwdriver.. and then tap on the screwdriver with a hammer to chisel out the blockage.

The cool thing for him is that it is going to cost him nothing and his ped is going to act like he put a turbocharger on it compared to before.

..and in a humorous tone >>

And...Yes... I agree... Steel wool is greatly underutilized resource... I think if it was properly utilized.. we could solve world hunger and political persecution and ethnic hatred.

I also find that it removes tooth decay and plaque very nicely... I use it on the end of a drill like you described.........yum!

Re: exhaust PORT carbon build up

To you both: Thanks for all your help..I used steel wool, an entire can of WD-40 and now its all pretty and shiny and basically carbon free. The carbon build up was from the people who owned the 'ped before me. They were so paranoid that the piston would seize that they always put in extra oil.

In any case, its all clean and running. Unfortunately its pouring rain out so I can't see how well it actually runs. I think the idle screw is gonna need an adjustment too..

Thanks again guys


Re: exhaust PORT carbon build up

Probably have lower compression without all that carbon on your piston head. Let us know how it turns out.

Just curious, but did you use the steel wool to polish the manifold and intake port, or just the carbon covered parts?


Re: exhaust PORT carbon build up

Reeperette /

Fyi....Dremel, and yeah...I polish those ports to MIRROR shine.

Know why ?

They do it to racecars for this little hair more horsepower, tis called a Port-N-Polish, as it were....I figure it ain't gonna hurt, and might even help.

Seems to reduce buildup rate too, not much to stick to, I guess, and that's a gooood thing.


port finish

It is the.. porting... on the "port and polish" that gets the HP increase.

("porting" is altering the shape and size of the tunnel the air flows through)

.. It is a fact that too smooth a finish in a port DECREASES air flow.

It is the exact same reason why a golf ball has a dimpled finish... because a smooth golf ball will not fly as far.

Professional race teams do not polish ports.

Local engine builders do it because their customers like it and think it looks cool.

Its like a Harley............. If it don't go.... chrome it!

Now... that was about PORTS... a head and top of the piston is a different story.

And polishing them does seem to give the carbon less to stick to.

But it doesn't change performance.

Re: port finish

Reeperette /

Oh, that makes sense, so they basically ream the port wider ? or just change the shape, or both ?

I have noticed less buildup tho, without any noticeable reduction of power...this is something interesting to play with tho.

Anyone ever tried port mods before ?


Re: port finish

Port shaping is a science unto itself.. and I wouldn't try to explain what I know ... ..and each motor is somewhat different.

The most important thing high performance engine builders (car and bike...2 stroke and 4 stroke)... offer... is porting... and a good porter usually specializes in one brand or type of motor... and has years of trying and testing experience...and a lot of pieces that were turned into door stops by a wrong move.

It all has to do with how air behaves while moving through a tube... and many assumptions most of us make... are wrong... like a polished port being better.

I mean... before people proved a dimpled golf ball flew farther... how many people would have answerd correctly if asked "Which will fly farther... a dimpled or smooth ball?".... I would guess... almost none (including me).

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