Carbon buildup on exhaust valve

K

Kevinpitta

Member
I purchased a new engine a few months ago and it felt down on power from the beginning compared to the well used one we ran last year. I did a leak down check on it this week and it was at 40 percent. I could hear the air escaping through the exhaust valve. Pulled the head and lapped the valves. I noticed a lot of carbon buildup on the back side of the exhaust valve. A lot more than I saw when I pulled the head from our old engine with many more hours of use. Only thing I can think of is a loose fit on the exhaust valve guide? Would running it with a valve leak have caused this? It now shows 3 percent leak down so the problem is resolved there, but still concerned about the carbon buildup.
 
you will say this is crazy but I have saved tons of time money and equipment by running water through the carb while keeping the engine running... I've done this on lawn mowers to exzotic cars ... and zero bad effects... did an 11hp honda pressure washer that was smoking like a train last week... now it purrs like it's a bear swimming in honey... used half of a bottled water... a ton of crap came out the exhaust... water does not compress (so don't use so much you hydro lock it) but a little at a time basicly blasts the inside of the combustion chamber and cleans the crap out... did an old $100 volvo in my teens and a full big coffee cup of crap came out the exhaust went from sounding like it needed a valve job/tune up wouldn't go 45mph to running very well...
 
Yes leaking valves will cause carbon to form under the valves. Are you saying you got the leak down from 40% to 3% by lapping the valves?
 
We used Sea Foam, poured it in a spray bottle and sprayed it through the carb and also ran it in our gas sometimes, just a little info for yah...:)...you can buy it at any parts house or even at War-Mart

We always lapped our valves about every 4th race and replace with new copper coated head gasket

https://seafoamsales.com/sea-foam-motor-treatment/

Click on Small Engines...2/4 Stroke Engines
 
That's funny, we clean out jet engines with a soapy spray then plain water rinse. Never thought about doing it to a piston engine.
 
sundog said:
That's funny, we clean out jet engines with a soapy spray then plain water rinse. Never thought about doing it to a piston engine.
Click to expand...

now i know i can safely do it to all my turbine powered vehicles... big weight off me knowing this :)
 
gary10 said:
Yes leaking valves will cause carbon to form under the valves. Are you saying you got the leak down from 40% to 3% by lapping the valves?
Click to expand...

Yeah....what Gary said...did you really go from 40 to 3 just lapping or were there other factors involved?
 
I'm guessing that the 40% number had the valve partially open. (Either lash too tight, or carbon chunk stuck under the valve.)
40% leakage would need the valve and seat re-cut in my experience (and more than allowable in the 206 class) - no amount of lapping would clean that leakage up.
Now, if the valve were held open (again, negative lash or chunk of carbon), sure, you could fix that easily.


-----
Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on FaceBook
29 years of service to the karting industry
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
Valve was not open when doing leak down. I removed rocker arms and locked crank down. Also pushed valve down and released several times with no decrease in leak down number.
 
I would suggest you do a before and after inspection no matter if you use water or another chemical.
If it's soft carbon you may have some success but if it's baked on i'd be very surprised if you remove any of it on the back of the intake or the exhaust valve.
The car companies use special blasting machines to clean the ports and the back of the valves. One of the mediums they use is walnut shells.
https://www.youtube.com/watch?v=KFvXbTIiAVY
https://www.youtube.com/watch?v=ONp6gQXpyKU
 
I don't know. I don't have a walnut blaster.
Another method is with a soda blaster but i don't have one of those either.

When you consider the time and labor cost some times its easier and cheaper to just replace them.
Then you have brand new parts without any guide or valve face wear.
The intake valve is only $10.47
The exhaust valve is $15.57
 
My point was if is allowed, opens the door to modification, hidden by the media blasting.

I guarantee, someone has insight on what will pass tech.

Not trying to start something, just saying these are the challenges in allowing such things.
The more people who understand this, the less chance some will try to get away with it.

I'm not intersted in cleaning the valves themselves, If I can clean valves in this manner, I will want to clean port as well.
 
From the Briggs rule set:
21. Ports
a. No de-burring, machining, honing, grinding, polishing, sanding, media blasting, etc.
b. The transition from intake bowl to port must have factory defined machining
burr at this junction.
No addition or subtraction of material in any form or matter.
No alterations of any kind may be made to the intake or exhaust ports.

e. Machining or alteration of any kind to the engine or replacement parts unless
specifically stated herein.
f. Deburring, machining, honing, grinding, polishing, sanding, media blasting, etc.
g. Sandblasting or glass-beading any interior engine surfaces.
h. No device may be used that will impede, or appear to impede, airflow to the
engine cooling system.

I have found many intake ports that have a carbon build up.
The way i clean them is to fill the port with carb cleaner and leave it soak for as long as possible. Then i use my finger to rub it until clean.
I do not use sand paper, scotch brite or any type of media to blast it for fear of changing the finish and making it illegal.
Time consuming? yes but i know it's legal.
Hard on my finger? YES
 
Jimbo said:
From the Briggs rule set:
21. Ports
a. No de-burring, machining, honing, grinding, polishing, sanding, media blasting, etc.
b. The transition from intake bowl to port must have factory defined machining
burr at this junction.
No addition or subtraction of material in any form or matter.
No alterations of any kind may be made to the intake or exhaust ports.

e. Machining or alteration of any kind to the engine or replacement parts unless
specifically stated herein.
f. Deburring, machining, honing, grinding, polishing, sanding, media blasting, etc.
g. Sandblasting or glass-beading any interior engine surfaces.
h. No device may be used that will impede, or appear to impede, airflow to the
engine cooling system.

I have found many intake ports that have a carbon build up.
The way i clean them is to fill the port with carb cleaner and leave it soak for as long as possible. Then i use my finger to rub it until clean.
I do not use sand paper, scotch brite or any type of media to blast it for fear of changing the finish and making it illegal.
Time consuming? yes but i know it's legal.
Hard on my finger? YES
Click to expand...

Now that makes better sense. It just seemed by the previous post that blasting was an option.
 
For those of you with engine refresh experience. I recently had my engine refreshed. The person doing it immediately noticed this when inspecting my head. What are your thoughts. He had not started to clean it. This is the condition of the head and ports Upon disassembly After 6 races.
thanks for your comments.
2D1E20CF-FEA4-4C35-BBAD-CEF42527F10F.jpeg
 
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