Carbon deposits

I think the answer is....nothing.

 

The deposits to some degree are unavoidable. Especially in the US where there is no chance to run it hard enough, often enough to prevent it. Making sure the carbs are really working well will very likely help. If it is heavy enough and if it is a problem its time to throw away the poor quality pistons and rings and replace them, then do a good valve job to it.

 

It's a normal feature of internal combustion engines. I think most of the buildup on the back side of the intake valves is from the PCV circuit introducing crankcase oil vapors into the engine to be burnt rather than wafting freely in the atmosphere like the old days. PCV was one of the first emission control devices implemented back in the 60's. Keeping the oil/vapor separator clean and functioning will reduce that somewhat.

Image Unavailable, Please Login

 

Engine warm and running about 2500 RPM, dribble some water into each carb throat.

Dribble, not pour. About 2-3 oz per cyl over 1 minute/cyl will clean the carbon right off. The water turns to steam in the carbon and blasts the carbon loose.

Doug

 

That's an old trick from the '60's and probably a lot older! When I was a teen we used to do it regularly though we never actually took apart an engine to see if it worked. Later, when I was older and actually built engines, I never thought of trying it. Can't hurt...unless you pour the water in too fast and hydrolock the engine! I suspect 3x8 connecting rods are expensive!

TBH, I wouldn't worry about some carbon on the pistons! Pretty much every engine I've ever disassembled had some.

 

I did that using a vacuum hose instead once on a 1969

Sent from my moto g power using Tapatalk

 

That's what the Seafoam treatment is, Seafoam is just "fancy" water. If it was just "plain" water well, you wouldn't pay for it would you?

 

Italian tuneup... a few hot laps a month keeps the carbon away!

 

Sorry @cbmcdona , sounds like you need a new engine... please DM me and I will take the old ride off your hands for a reasonable cost! (obviously JK) On a serious note, you could possibly use a hotter plug, also as described above, water and the Italian tune-up!

 

Remember - a "hotter" spark plug means the plug tip runs hotter and can reduce plug fouling but it has no effect on the temperature of the combustion chamber/carbon deposits on the piston - that's a function of the fuel/air mix plus however much oil finds its way into the combustion chamber.

Some carbon on pistons with mileage/average use is normal; excessive carbon on the pistons indicates a problem with cylinder sealing/valve guides/valve seals.

 

@mike996 you bring up a good point, and I really love the forum, but it's SO hard to diagnose the OP's issue of "carbon deposit removal" on a carb 308. There are multitudes of variables on this 40+ year old car: miles, tune (plugs, A/F, timing, jetting), driving habits, Euro or early or late US car, type of gas used, modifications or not, etc., etc.. Pics of the carbon deposit would be helpful, but still highly subjective...

 

I've cleaned a lot of fouled pistons with significant carbon deposits, and had to soak them overnight in a bath of throttle cleaner just to make a dent in the carbon, followed by an hour or two of scrubbing and resoaking. I cannot imagine that introducing seafoam or 3 oz water into the combustion chamber offers any measurable benefit.

 

Oh it does, take a look at what water does to seaplane propellers. Also a method of detecting a blown head gasket is a shiny piston top. I mean, look at the Grand Canyon, water did that.

 

I've seen a friend literally pour a glass of water down the carb of his '70 442, revving it while pouring the water, blowing carbon out the exhaust. This was at least 30 years ago.

 

Did it remove *all* the carbon from the piston face? If not, it created a hot spot.

 

If you have ever disassembled a motor that had leaky a head gasket into the cooling system, you KNOW that water works, the piston tops and combustion chamber are almost squeaky clean in the offending cylinders.

Doug