69 Z is running rich

[wisemanz28]

Ive been trying to figure out why my 302 is running rich and fouling out my plugs. Today I put on a vacuum gauge and it read 20 to 22 and the needle was not steady, it was bouncing. I thought maybe the valve's needed adjusting , did that with no change. I'm not sure if its in the carburetor. Plug wires are new, points were cleaned and reset, distributor cap looks good. Looking for suggestions.

[dannystarr]

I am not an expert. But I can tell you I learned the hard way to ALWAYS check fuel pressure BEFORE you do ANYTHING else. I check it in actual working conditions. I see people plug the line with a gauge near the carb, and fire it up and read it, and think that is the pressure. With it pumping against a stop. That's NOT actual operating flow through pressure. I have tried it 3 times BOTH ways and it always has read different. Run it up to the windshield and back down. JMO... Danny
   
       https://www.youtube.com/watch?v=QdEhsJqryNc

       https://www.youtube.com/watch?v=JwxHpvT9vP0
 

[Stingr69]

First thing, 302 will not pull 20-22 on a vacuum gauge.   

Verify the float setting before doing anything else to the carb. 

Pull the plugs and see if they all look the same. 

[wisemanz28]

Adjusted the floats, the rear was too high and the vacuum needle is bouncing  between  19 and 21. I  could be misreading the guage,  what should be a normal vacuum reading for a 302?

[crossboss]

Hi performance engines regardless of the brand will produce vacuum readings around 12-14 on the gauge. 'Race' engines like L88s, ZL-1s, and 427 Cobras much less. Your average run of the mill engine in a passenger car will produce around 16-22. Higher with hydraulic cams, A/C, automatics, P/S, P/B, you get the idea.

[wisemanz28]

I have a picture of the guage reading but the file is to large to post

[crossboss]

I have a picture of the guage reading but the file is to large to post

Two things are wrong here: 1-your gauge is incorrect. 2-And/or your camshaft is not correct. There is no way a stock DZ cam will pull 22 on a vacuum gauge. Something is amiss here.

[wisemanz28]

As I mentioned in a prior post I'm not sure I'm reading the guage correctly,  I tried to post a picture of the guage but the file is to large. There is two sets of numbers on the guage, the outside number  reads 20 , the inside number reads 8. Apparently I read it wrong. The car is all stock and I've owned it for 32 years

[jdv69z]

Stock 302 with stock cam, carb etc., will pull 8-11 Hg at 900-1000 idle RPM

[Kelley W King]

Now that you are on the right scale, the bouncing could be valve problems. A valve that is burned, cracked, or other not sealing can let a shot of compression blow into intake area.

[jdv69z]

How about a failed power valve? Vacuum holds the valve closed. When vacuum drops below the power valve setting, think acceleration, (65 Hg on a stock Z) the valve opens adding additional fuel. If the valve diaphragm is ruptured the valve is open, adding additional fuel constantly, even at high vacuum, think idle, richening the mixture, when it is not needed or wanted. If the car ran OK, and then something changed, this could be it. Sometimes the power valve fails due to back firing.

[327Dean]

Its really gotta be the carb, the only other thing would be a plugged air filter (doubtful).  Is the running rich, fouling plugs a recent development? 

Couple other checks: Choke is wide open when warmed up; No fuel dripping in primary or secondary barrels at idle;  Air bleeds clean.

Dean

[z28z11]

In addition to the carb needs, what's your operating temperature and what heat range (and manufacturer) of plugs are you using ? 165 degree thermostat and cold heat range plugs will gas foul if you look away for a split second. Initial timing ? What gas and octane rating ? Stock or old (weak) coil ?

I agree with the power valve rupture possibilities - one good hiccup or backfire, and you can pop one. You can always add a blow out preventer from Holley to help keep that from happening again if it has.

Good luck -

Regards,
Steve