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.

[Spoke]

Hijack (again):

On my 2056, I have some popping when the engine is pre-warm. No popping after warmed up.

Carb settings:

Weber IDF 40
28mm venturis,
115 mains
Idle Jets: 50
airjets 200
F11 emulsion tube

Recently adjusted valves (didn't change anything)
No vacuum leaks.
No info on cam or valves. (2L heads)

Adjusted the idle vacuum for each side and idle bypass screws were all about 1 1/2 turns out. Engine ran pretty good.

Then about a week ago, it started running very rough, like on 3 cylinders when at idle and light throttle. With heavy throttle, it pulled like crazy.

Seemed like #2 was not firing. On cold start up and just idling with some revving, I checked the temps of the exhaust pipes and #2 pipe was cold. Pulled the plug wire while running (using an insulated hose pliers) and the engine slowed down a bit so the plug was firing.

Sprayed carb cleaner on all the intake interfaces and no change in engine tune so likely no obvious vacuum leaks.

I backed out the idle screw many turns and the engine smoothed out at idle. Took it for a ride and it ran ok; not great; just ok. Exhaust tubes were all similar heat so #2 was firing ok.

I'm going to pull the carb and inspect. What should I be looking for?

[Superhawk996]

I'm going to pull the carb and inspect. What should I be looking for?

@spoke

No need to remove the carbs yet.



Pull idle jets - clean and blow out with air
Edit: CRITICAL - limit air pressure to about 2-3 psi - ie very gentle. With fuel still in the bowl - blowing air though the idle passages will pick up some fuel out of the bowl - short bursts - not extended blowing though the passages - we are only clearing minor debris or corrosion particles. And should go without saying don’t do this in the presence of sparks or flames!

Blow air though the idle air correction bushing (non removable brass bushing at top)

Blow air through the idle jet hole.

Remove idle mixture screw(s) - clean; inspect. Often you will find some rust or corrosion on the needle. Clean up with steel wool or 3m scrubbie.

If you find heavy corrosion on a needle it may need to be replaced but not usually. Likewise, if there is heavy corrosion on a needle, spray carb clean into the hole to help break up any corrosion in the idle port then blow again with compressed air.

Blow air though the mix screw hole to clear the idle port and transition ports of any debris or corrosion.

Reinstall everything; set idle mix; resynch carbs

All this can be done in car without need to remove carbs and linkages.

[Spoke]

I'm going to pull the carb and inspect. What should I be looking for?

@spoke

No need to remove the carbs yet.



Pull idle jets - clean and blow out with air
Edit: CRITICAL - limit air pressure to about 2-3 psi - ie very gentle. With fuel still in the bowl - blowing air though the idle passages will pick up some fuel out of the bowl - short bursts - not extended blowing though the passages - we are only clearing minor debris or corrosion particles. And should go without saying don’t do this in the presence of sparks or flames!

Blow air though the idle air correction bushing (non removable brass bushing at top)

Blow air through the idle jet hole.

Remove idle mixture screw(s) - clean; inspect. Often you will find some rust or corrosion on the needle. Clean up with steel wool or 3m scrubbie.

If you find heavy corrosion on a needle it may need to be replaced but not usually. Likewise, if there is heavy corrosion on a needle, spray carb clean into the hole to help break up any corrosion in the idle port then blow again with compressed air.

Blow air though the mix screw hole to clear the idle port and transition ports of any debris or corrosion.

Reinstall everything; set idle mix; resynch carbs

All this can be done in car without need to remove carbs and linkages.

@Superhawk996

Thanks for the tips. About the idle jets, are they where this picture has the vacuum hose? I'm not well versed in carbs but I did stay at a Holiday Inn Express sometime in my past.