After all this fun with a snapped rocker arm bolt and bent pushrod (loose rocker arm bolt, I think), I fixed the valvetrain and fired 'er up again. Sounds great, no issues mechanically with the motor (360 Magnum). The fuel, however, is a being a brat.

Some of you know that a couple weeks ago I had carb vacuum problems which left me stalled in the middle of the road, and resulted in a AAA tow and my swapping to an Edelbrock Performer carb for the time being. Since then, I have been having interesting idle issues. For the first few minutes after starting up cold, it would idle really rough and almost die. I would just hold it to 1000RPM until it warmed up, at which point it would idle fine (1000RPM in park or neutral, 850RPM in gear). By cold, we're still talking 85-90 degrees outside, but this happens if it hadn't been started up in a while.

So about a week ago, I got out my trusty vacuum gauge and tachometer, which had both been verified to be correct against another gauge, and set the idle at a basic level. I started from a baseline of 850RPM (in park) and leaned out the engine until I got the highest vacuum reading. This boosted my idle speed a bit, so I brought the idle speed screw down until I got back to 850RPM. I plugged the rest of the vacuum ports, plugged back in my vacuum advance, and she idled like a dream, even though the exhaust still had a gassy aroma to it. I drove it around a bit, then pulled a plug - carbon-fouled. Well, I decided to drive it around a little longer. I did a healthy 2000RPM all around town - maybe a 20 minute adventure - and came back. Still carbon-fouled plugs. No gasoline smell, no wetness, just carbon. This was Monday of last week, but since I had a lot of stuff to do (read: prepare for a vacation this past weekend), I let it sit until yesterday.

The idle issue wasn't a problem before, as when it would warm up, it'd idle just fine. That is, until yesterday. After the car warmed up, it still wouldn't idle. It sounded really rough, and strangely quiet from the tail-pipes. In park or neutral, it was averaging about 850RPM, but would spike 200 RPM or so either way. In gear, it would peak at 500RPM but always try to die unless I gave it gas. If I poked the throttle, nothing would happen. It actually seemed like there was no combustion for a revolution or two after I poked the throttle. However, if I eased on the throttle, I could get the RPM up again. I was thinking vacuum leak, but with the vacuum hovering at about 15hg, I kind of ruled that out. Was I wrong to?

A couple other symptoms I've encountered: I have a fuel filter inline between the fuel pump and the carb. I am getting a bunch of grit into it, and the filter's basically brand new. I need to do something to my tank, but is it possible to get the stuff out, or should I just buy a new tank?

Also, when it starts up cold, the fuel filter (which is clear) shows the fuel as very agitated coming up into the filter. It's almost like it's bubbling to the point of spraying through the filter element. It's not hot, as I'm able to feel the fuel filter itself, so I don't think it's boiling. But it's definitely drawing a LOT of air through. I know I have fuel in the tank (I just put 10 gallons in), so if it's drawing air, I don't know where it's coming from. I don't have the vapor separator line connected to the air cleaner or anywhere, but I don't have it plugged either, is that a problem?

Not sure what my issue is, but at this point, even with a really lean engine at 15hg of vacuum, it's still having idle issues and still fouling plugs. Any advice is appreciated. I'm almost ready to get out the checkbook and place an order for an Innovative LM-1 to REALLY tune this thing, but I'm thinking that this should/could be corrected in a much simpler and cheaper manner. Thanks in advance!

Unless you've got a pretty decent sized cam in there, your idle speed seems kind of high--you might not even be on the idle circuit. Put a fresh set of plugs in it and go for a cruise with a little more RPM--not full throttle but enough that you know you're not on the idle circuit. THen shut it down and pull the plugs immediately. If they're black, you're too rich on the primary circuit.

Do eddy's have a power valve in them? If so, that could be your problem. You have the wrong vacuum rating on it.

Nope. No power valve. That's the reason I went with one while I rebuilt my Holley after it was causing problems..

Oooh good information, thanks guys. My Edelbrock doesn't have adjustable float bowls. I don't think the cam is too big, it's a Hughes 1418ALN:

Camshaft Technical Details

Intake Valve Lift 1.6 .520"
Exhaust Valve Lift 1.6 .544"

Intake Duration at .050" 214°
Exhaust Duration at .050" 218°

Lobe Separation Angle 108°

Sweet Spot RPM 2300 - 6100

You do have adjustable floats but you have to take the top off the carb to set them. All floats are adjustable in some manner.

Oh yeah, I forgot about that little tab on the float.

If you're pulling anything over 12" Hg then your cam is not too big. Those carbs don't like vacuum below 9". And they don't like excess fuel pressure either; I believe 6 psi max. I tried in vain to tune an AVS on a 7" Hg engine...

You may need more initial timing to start and then a recurve.

Oh, I should mention also my fuel pressure gauge, when working correctly, sits nicely at 6psi. When not working correctly (the time that I notice idling issues), it sweeps violently between 6psi and 15psi. I think this may be a problem related to air in the fuel line?

Is your tank vented? you could be building up extra pressure. I once raced with a guy that would take his gas cap off then wait a second or two before each round...I asked what are you doing? he said...car likes to build up pressure, this gets it out?????

""""EDDY'S EDDY'S EDDY'S""""""

How about Caterbrock?

I wonder if it is the pressure issue. Especially if it's push 15 at times... You could try a fuel pressure regulator.

I don't think it's pressure. I think the fuel pressure gauge is going wild because there's air in the line.

The only thing not counted was that we think the mysterious reason was actually a vacuum leak in the secondary diaphragm.

I know it sounds like a fuel pressure issue, but how could a mechanical fuel pump possibly be getting that much pressure built up? Similarly, I shouldn't say the needle sweeps up and down the gauge. It looks more like a severe rattle in the range of 6psi to 15psi. It doesn't do a smooth sweep like a speedometer or a tach or anything.

You went to the trouble of installing a fuel pressure gauge, and are now pretty anxious to ignore or explain away what it's telling you.

If the gauge sees 15psi, so does the carb, whether it is smooth or spiky.

Running without the gas tank cap for a period of time would rule out the possibility of a pressurized gas tank.

That would take one thing off the table.