TheSamba.com :: View topic - carbon build-up on intake valve

Wed Aug 17, 2016 9:37 pm

how did this happen

intakes--before and after

closeup

working on it

thats a lot of carbon!
any ideas?
i was rich on idle jets(55 going to 50)
low compression 7.0(going to 9.0)
was the valve glowing hot sizziling the gas(cooking on valve)?
cheap gas(i do run premiun)
oil coming down valve stem?

Thu Aug 18, 2016 12:05 am

Most of the intake valve currently existing are like that more or less.
How does it happen? chemistry? heat? I think the fuel hits the valve and makes it sticky, then the small puffs of carbon which blow back tend to stick to it and build up.
They have a little display at the shell gas station with a carbony valve and a clean one and it says our gas "reduces deposits 35%" or something, and I thought that was rather funny, because the 'bad" valve in the display was rather typical, no worse than most. I considered getting them a better example, perhaps a detroit diesel, looks like a soot popsicle :lol:

Looks kinda fluffy like the deposits in a smoker I was fixing a few weeks ago. mmm, pork carbon. Not only does it make good flux for shielding the back of the weld, but it also delicious flavor too. when they run bio diesel sometimes it imparts a bit of flavor.

Well, if the chambers were extra fluffy too, then we'll blame that for the 30% beyond normal buildup. Running rich will make a lot more carbon, and you could blame the gas also, they are supposed to have some additives in there to minimize the buildup, and certainly not all is created equal. Some OE cars had problems, when the deposits get out of hand it was found they can act as sponges and delay fuel delivery. We've come a long way from when you had to take apart your model T engine and scrape the gunk out of it every 1000 miles!

Thu Aug 18, 2016 5:44 am

Do you have your crankcase vented to intake? Oil vapors will tend to do that.

Thu Aug 18, 2016 8:40 am

and some additives will also do that :shock: lucas/mucas is real bad about it. and remember if you buzz up your motor all that carbon is added weight to the expensive lightweight valve train you paid for..... for the most part I think it's when you turn off the motor that it stays there and dries the fuel aditives that are supposed to stop that. I remember years ago a big engine builder was doing a lot of testing and found the carbon buildup was a direct result of dried fuell additives in conjunction with stagnate areas in the chamber(not enough squish/wide deck) and fuel drieing when the engine was turned off. just look at the fuel residue around the carbs that dont leek but vapors leave a visual of the residue.ones that leek are worse. when the fuel all burns it go,s out the exhaust. when parts dont burn you get depisits. when there is a stagnate area in the chamber that dosent get swept out the exhaust and the incoming mix is diluted and dosent burn and deposits are formed. walls&sharp edges on those walls can create something like a EDDY in a stream. where that portion just stays there as the rest go,s down stream. Oil also forms deposits.as can fuel droplets that are not attomized. thus one of the reasons for bigger air jet to help atomize the fuel better.and with the biger air jet a bigger main jet is needed due to the air jet adding more air....automizing better.witch is more torque.higher cr also makes more torque and runs cleaner too....when done right. Ok Ill shut up now. gotta get back to work.

Thu Aug 18, 2016 9:01 am

it will do that if it's way too rich, and/or the CR is too low for the cam being used.

FWIW, a bottle of Gumout Regane will remove it all in 1 tank of fuel.

https://www.amazon.com/Gumout-800001364-Regane-Complete-Cleaner/dp/B004361AFQ

Your local FLAPS may have it too, they do at our Pep Boys.

Thu Aug 18, 2016 7:18 pm

As John noted....being rich...and/or having rather low combustion efficiency due to excessively low compression are the classic causes of excessive carbon build up.

Personally....that carbon buildup looks a lot like oil. Tylically if your valve guides are just a hair on the loose side, excessive oiling of the valve stem will work its way down the valve and carbonize. It can also be layered with varnish from fuel additives and alcohol.

There are other newer causes of carbon as well. Part is modern fuel related.

Very modern cars.....most especially those built say in the last 10-12 years are having carbon issues.....especially intake valve carbon build up....especially the direct injection engines....mostly because of the oil seepage down the valve stem and the fact that no fuel flows past the valves with detergents to keep the oil washed off of them before it can carbonize. Ray

Thu Aug 18, 2016 9:09 pm

Use the best fuel you can find. I like Chevron with Techron or Sunoco 94.....Also Liqui-Moly makes a product called Ventil Sauber.......I think in German it means "valve cleaner"

Thu Aug 18, 2016 9:14 pm

Use the cleaner that John suggested: Chevron Techron Concentrate; Gumout "Regane"; and Redline Fuel System Cleaner all use the same cleaners that do work.

Thu Aug 18, 2016 10:28 pm

the pic of the dirty valve--should of noted--i had it soaking in acetone and just took it out.
you can see small droplets on stem and makes it look shiny.(eco. friendly junk)
the carbon would only come off manuelly( razor & fine sandpaper)
i have been doing most my driving on low to moderate rpm's running on my overly rich(for my mtr.) 55 idles (duel 40mm carbs.)for a while.
the doc. says go 50's and that's what i got in em now.
thanks for the input.
with a fresh start, and proper combo's (compression & jetting)
this baby should rock when i want it to! 8)

Fri Aug 19, 2016 2:14 am

Cam, valve size, exhaust and port size can influence. If you have high airspeed in the intake, and no reversion from whacky cams/ exhaust, the air in the intake port moves mostly one way, leaving little or no residue on the back of the valve.

Most performance cams have quite a bit of overlap, and depending on the combo, some very funky things can happen at certain RPMs.

Fri Aug 19, 2016 3:25 am

Under light load conditions, inlet ports are seeing a partial vacuum. Oil gets drawn via inlet guide, and some could end up on backside of valve.

For a special application i am considering valve stem seals, like ones used by the 911, only for the inlets. But having my doubts... This is an experimental mileage engine.

Found that when combustion chambers/valves were freshly polished, engine would tolerate a degree or two more timing. But only for the first 5000- 10000 miles, until normal light deposits are formed. After this it's back to normal standard knock sensitivity, but doesn't get any worse from there. At around 50000 miles i removed heads for inspection, and polished chambers. Thereafter had another few thousand miles of slightly more knock-resistant conditions like before.

Maybe it's a better idea to rather use a good cleaning additive from time to time, or dump some cleaning chemical through inlets while engine is running...