Single Hot/Lean Cylinder

[TheUglyVW]

Hey all, I am at a loss and coming here for some expertise.

I just build a brand new motor for my VW, 1849 (76x88 thick wall). New heads from AA, CB Performance CW crank, AA cylinder and Piston kit, Engle 110 cam.

I noticed one cylinder (#2) running hot, and based on the spark plugs and exhaust valve. I also measured the header temps, #2 is almost 150 degrees f hotter.

I am super confused, because I am running dual kads. Since Kadron cards are single barrel, one barrel feeding two cylinders, I don't understand how one cylinder can be so lean.

I checked all my gaskets, sprayed carb cleaner around looking for a vacuum leak but cant find one.

I did a compression test, getting 130PSI on all 4 cylinders cold.

I took the heads off to look for any combustion leaks around the heads and cant find any evidence of one.

Maybe its an ignition issue? I timed for full advance at about 32 degrees, but maybe my electric ignition is running higher advance on #2?

I am at a loss. Attached are some photos for refference.

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[rcooled]

That black carbon build-up is usually an indication of an overly-rich mixture and/or incomplete combustion. That blackened chamber in your photo appears to be from either cylinder #1 or #4, and it would be running cooler, not hotter. Is that the one you think is running too hot? The slightly cleaner chamber would be from either cyl #2 or #3, and looks pretty much as it should.

Where exactly are you measuring the exhaust temperatures? If you measured #2 right where the header attaches to the exhaust port, then measured #1 where the header meets the heater box (assuming that you're running heater boxes), there should be a considerable difference in temperature as the exhaust gas from cylinder #1 will lose heat as it passes thru the heater box.

You might check the spark plug wire that runs to that blackened plug...that's the cylinder with a problem. Could be that there's a weak spark there causing it to soot up like that.
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'63 Ragtop (current)
'65 Ghia coupe (totaled)
'67 Ghia convertible (current)
'69.5 Ghia convertible and
'62, '63, '65, '69 Bugs (all long gone)

[TheUglyVW]

[rcooled]

[AlteWagen]

Seems AA cylinders have high frequency of casting pinholes in the cylinders. It would cause the condition you are describing
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[VW_Jimbo]

Running too rich. On 2 single barrel carbs, there is ALWAYS a weak cylinder and a strong cylinder. So they most often look different.

What you are seeing is an overly rich, too much fuel, poor spark quality, misadjusted valves, or too high of fuel pressure. Kads are really sensitive to that last problem. REALLY SENSATIVE!

What is your fuel pressure out of the pump running? If it is over 2.5 - 3psi it will overwhelm the needle valves in both carbs. Kads are sensitive! Get a fuel pressure gauge and T it into the output side of your pump. If it is over 3psi, hell I would be shooting for 2.75psi, it is too high. Get a Holley fuel pressure regulator and install it. Dial in the pressure to 2.75psi. Then reset all those basics.

Plus change your oil because your crankcase is full of gas. Smell your dipstick or just check the level.

Good luck!
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Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!