Porsche 914-4 Weber Carb running rich, Weber Carb running rich on #4 only Options

[mturner7]

Hi Everyone,

My car is a 1974, 914-4 with a 2.0L (2056cc) engine. With Weber IDF 44's.
My #4 cylinder is running really rich. All the others are fine.

The Question is: What in the carburetor could most likely cause the plug to foul (Running very rich) like in my case? I've tried to adj the air/fuel mixture screw still no change.

This is what I've done so far:

0) Did a compression check on all cylinders. All ok. (95-100psi) 
1) Changed the plugs.
2) Changed the Cap and Rotor.
3) Changed the plug wires.
4) Verified all the jets are the same.
5) Set the Air flow on each carb, sync'd them
6) I cleaned all the jets with the carb in the car, ran and idled much better.
7) Verified Spark to that Cyl, got a hell of a shock out of it.
8) I'm running Elec-Ignition, Flamethrower Coil, 60,000volts.

After doing all this, the #4 plug still fouls after only about 20 to 30 miles. It has to be the carburetor.

I just pulled the carburetor. Thanks for the help.

[technicalninja]

If anything I would go with 28mm venturis, not 36's

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Do they make 28mm vents for the 44 IDF?

Smallest I've found is 32s for the 44IDFs

Mturner7, the reason the mains were so large was the previous owner tried to add more fuel to a carb size up that was poorly matched to the engine it was on.

The real problem was too little vacuum at the booster.

You put the basic stock jets back in it and now you do not have enough fuel in the upper end.

That carb should be on a 2.2l or bigger street motor.

It would work on a 2.0l competition engine. I would expect a power band from 4-8K only.
Below 4k it would be a dog...

You need a higher vacuum signal. These are the only ways I know how to do that.
Increase engine size or RPM range (increase airflow).
Decrease butterfly and venturi size. I think you're already on the smallest vents available for your 44s.

Some carburetors have special auxiliary venturis that are "dog legged" deeper in the main venturi.
Some have annular boosters. Makes TBI style spray from the boosters.
Don't think either of those are available for the IDF series.

Bottom line, carbs are too big for a street based 2 liter...

The funkiness with cylinder #4 may be something different but having badly matched carb to engine size would make diagnosis far more difficult to do.

The change back to the proper size mains is probably running the engine way lean (your loss of power) and may be running it way too hot.

A WB02 sensor and a good CHT gauge should be part of any serious tuning IMO.
Extended use above 400 degrees will hurt the metallurgy of the air-cooled heads.
It looks damn easy to hit this number with a slightly improper tune.
I would guess yours is WAY off...