Carbon buildup in carburetor

[Dave Pratt - IL]

A friend was telling me that he had to open the fuel adjusting valve several turns to get his car to run and that it would not idle. He thought there was a problem with the carburetor. He dropped off his carb for me to look at. I opened it up tonight and can not believe the amount of carbon buildup in it. It looks like the inside of a tailpipe. The idle, cap and main jets were all covered. After cleaning it up, I can find nothing else wrong with the carb. All the passages are now open and jets (original) are the correct size, float set right etc. What could cause this much carbon buildup?

[Kurt in NJ]

Is it black carbon ---or is it a dark brown goo ---if i leave the gas on untill i get the car parked, then shut it off I have gotten a dark brown goo that has drooled down the jet, and clogged it up, it only started happening in the past 3 years to me, something in the "new" gasoline when it evaporates leaves it.

An exhaust leak blowing out soot --that getting sucked into the carb??

I have seen camshaft, and valve seating problems fill intakes with carbon

[Mike V. Florida]

Originally Posted by Kurt in NJ;

An exhaust leak blowing out soot --that getting sucked into the carb??

That's my vote! Leak at the manifold muffler connection.

[Jim/GA]

Look for a bad distributor cap. Sounds like cross-firing to me, blowing the charge back out of the intake valve. Might only happen with spark rod at one extreme end or the other.

[Dave Pratt - IL]

Originally Posted by Kurt in NJ

Is it black carbon ---or is it a dark brown goo

It is as black as can be.

[ford1]

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the only way carbon can get into a carb is thru the intake valve , sticking open or burnt, run a compression check on all cylinders

[Bob A.]

Originally Posted by ford1

the only way carbon can get into a carb is thru the intake valve , sticking open or burnt, run a compression check on all cylinders

In addition to what Ford 1 stated, weak intake valve springs too. A vacuum gauge test would be a worthwhile test.(somewhere around two to seven inches fluctuation below normal indicates poor valve condition)

[Steve Wastler]

[QUOTE=Kurt in NJ;43785]Is it black carbon ---"I have gotten a dark brown goo that has drooled down the jet, and clogged it up, it only started happening in the past 3 years to me, something in the "new" gasoline when it evaporates leaves it."

Kurt,

I think you may find the 10% ethanol in the new unleaded is melting off some old carmelized gas in the tank and or gas lines.

The mail truck had sat for about 25 years with gas drying up in the tank. It was an almost hard molasses about a quarter inch thick over the entire bottom of the tank. I bought a couple of gallons of the E85 ethanol and poured in the tank. It works well to disolve the molasses, and doesn't need agitation.

I have added and drained 1 1/2 gallons let sit for a week and repeated twice, the molasses is just about gone and the tank is looking pretty good.

You may want to peer inside your tank, if you see any darkining on the bottom you may want to drain and give it a try. Just my two cents, It has worked for me.

[Jack '29 Sport Coupe]

I dump an ounce of "Star*Tron" in each tank of gas. It's a product made by
Star Brite and is available at Walmart in the boating section. It keeps my tank
and carb clean as a whistle. You can download the MSDS information on the
website. JMHO

Jack