Plugs fouling newly rebuilt '67 318

[67D100Pickup]

Ok. I asked why spark plug wires would stop firing and it turns out spark plugs were fouled, in four cylinders.

Why are the plugs fouling?

I found that the electric choke was not connected and therefore appeared to be fully closed all the time.

I connected the electric choke and put new spark plugs in.

After about 20 miles the plugs are fouled so bad again it is already missing.

Plugs are covered in black suit.

What could be fouling the plugs now? Did I ruin the engine build? Are the rings shot? Are the valves shot?

Could the carb be oversized? Need smaller jets? Could too rich a mixture foul plugs that bad that fast?

Jeff

[sixpak340]

20 miles is not much, rings need time to seat.

What type of oil is in it?

[67D100Pickup]

I don't know what kind of oil the machine shop put in it.

He said leave it in 500 miles though.

[PwrWgnDrvr]

Blue smoke out the tailpipe - burning oil. Black smoke - burning gas, too rich. Either will foul the plugs.

[my5thmopar]

Who broke the engine (cam) in and how did it run. Sounds like a poor adjusted carb, bad, or too big. What’s carb is on it? Can you borrow one from a buddy to try? In the other thread you said the plug wires are ok? Keep all this in one thread so we can follow and help. Craig

[67D100Pickup]

Sorry. I thought since I solved why the plug wires were not firing I should start over with why are plugs fouling.

Edlebrock with Holley 670 and Hedman headers. Estimated 280 HP.

I broke in the cam. We were supposed to run it 20min around 2000 rpm with an occasional light bump, cool and repeat.

What actually happened was the PCV valve was creating a vaccum leak and we wound up running it closer to 2500-3000 rpm.

Also, we ran the break in with timing at 5BTDC. I learned later that should have been about 18BTDC with a target of 34BDTC all in after mechanical advance but it seemed to run smooth.

I *think* where I'm at now is

1. install new, correct plug wires for a Mallory Unilite ignition.

2. set timing to 34BTDC, all in after mechanical advance.

3. Check idle metering

4. See how that went?

Does that sound right?

Jeff

[my5thmopar]

Looks like you’re going in the right direction. I’m still leaning towards a carb issue since the plugs are fouled. Is the carb new? It could be weak spark but I think you would have missing issues too. How much vacuum do you have at idle? The 670 is probably not too much for a healthy 318. I used a 650 Edelbrock and had to jet/rod it down. I was using an AFR gauge though. I’m not a good Holley guy but I have run them in the past. I’m thinking you should round up another carb to try. Check that you’re on the timed port, the transfer slots and the float level. Does the mixture screws work and kill the engine when closed? If not then the PV may be bad or too big. That’s all I have, so maybe a Holley guy will chime in.

[67D100Pickup]

Yes, carb is new. And yes, it misses but I think only after running a while, and plugs start to foul.

I'll chase down your other questions and update...

[67D100Pickup]

I have only adjusted the idle mixture screws one at a time so far. And no, fully closed doesn't kill the engine.

Am I supposed to adjust them all down *evenly* until it kills the engine?

[swptln]

Did the engine ever backfire, while you were breaking it in or trying to start it at anytime?
Holley's have a vacuum operated power valve and if the engine backfired just once, it can blow the power valve and make it run excessively rich.
If not, I'd be looking at jets, sounds like it's one of the two causing the plugs to foul.

[swptln]

I have only adjusted the idle mixture screws one at a time so far. And no, fully closed doesn't kill the engine.

Am I supposed to adjust them all down *evenly* until it kills the engine?

Turn them all the way in, back them out 1.5 to 2 turns, warm up engine to operating temp, turn them in slowly till engine starts to die and back them back out till it runs nice and smooth.....should use a vacuum gauge and set them with the highest reading of vacuum at idle.
It should start to stumble the engine when there almost all the way in....you should hear a difference even with just one. If it doesn't make any difference, your carb is pulling fuel through the main circuit or in the case with a Holley it could be the power circuit.
When the throttle plates are closed at idle, your power and main circuit should be dead and no fuel flowing through it, just the idle circuit.
Also, check your float level too, to high a float level will dump gas into the venturi's. Set your float level with the bowl level caps on the side of the bowls.

[67D100Pickup]

Did the engine ever backfire, while you were breaking it in or trying to start it at anytime?
Holley's have a vacuum operated power valve and if the engine backfired just once, it can blow the power valve and make it run excessively rich.
If not, I'd be looking at jets, sounds like it's one of the two causing the plugs to foul.

It is hard to recall but I believe it has backfired. Probably while we were screwing up the timing. I'll add that to my list of stuff to check.

[67D100Pickup]

I will check on that.

[712edf]

I would recommend putting in a power valve plug in the Holley until you get this straightened out, then go back to a normal valve, based upon vacuum readings.

Bucky

[67D100Pickup]

712edf and swptln win the gold star on this one.

Plugging the power valve did the trick. I don't know if I blew the PV out or not but plugging it worked.

The holley site says they've added a check ball to keep backfires from ruining the valve, but how can I confirm if the valve I have is bad or if its good (and it's just the wrong size or vacuum rating)?

Jeff

[712edf]

It takes a vacuum gauge, preferably one you can read while driving it, to determine the correct power valve needed, if any.

If a carb is too large for a particular engine's needs it might run better with just the plug.

The power valve is an gas enrichment part of the carburetor, keeps it from leaning out during times (part throttle) when the vacuum drops. It supplements the amount of gas delivered. Serves a similar purpose as the accelerator pump but does it by a different method.

Holley's website explains this better & tells you how to diagnose the Power valve's condition.

I would get the truck running good with the plug, use a vacuum gauge to figure out where your particular engine is at, then start fine tuning with the correct power valve.

Bucky

[67D100Pickup]

I have only adjusted the idle mixture screws one at a time so far. And no, fully closed doesn't kill the engine.

Am I supposed to adjust them all down *evenly* until it kills the engine?

Turn them all the way in, back them out 1.5 to 2 turns, warm up engine to operating temp, turn them in slowly till engine starts to die and back them back out till it runs nice and smooth.....should use a vacuum gauge and set them with the highest reading of vacuum at idle.
It should start to stumble the engine when there almost all the way in....you should hear a difference even with just one. If it doesn't make any difference, your carb is pulling fuel through the main circuit or in the case with a Holley it could be the power circuit.
When the throttle plates are closed at idle, your power and main circuit should be dead and no fuel flowing through it, just the idle circuit.
Also, check your float level too, to high a float level will dump gas into the venturi's. Set your float level with the bowl level caps on the side of the bowls.

More follow up... I think the carb IS oversized so it can perform better at wide open throttle. I asked the builder to build a good street truck that runs good:-)

It idles with best vacuum/idle speed with the idle jets 3/4 turns open and no power valve. I haven't confirmed yet if my power valve is blown but it runs great with that plugged so I will leave it plugged until I get everything else stabilized.

I'm really cautious to buy gauges because I have no knowledge in these matters and I don't really know what is appropriate for this engine.

Just vacuum? Vaccum plus tach? I like my stock temp gauge even though it doesn't have numbers. It does show "normal " and indicates if the engine is running hot. Same with oil pressure dummy light. It seems fine to me that it alerts only if pressure is low but would any knowledgeable operator add a pressure gauge?

Now vacuum? tach? temp? oil pressure? Others?

So many options for a novice to shift through.

Maybe someone here can just forward a link to the right gauge cluster or set that would work well?

Jeff

[sixpak340]

Just curious, but you said "plugs were fouled, in four cylinders".

All four on one side or mixed side to side?

[67D100Pickup]

It was the front four cylinders, 1..4.

Jeff