I had a miss today so I decided to change my points(no electronic ign yet. Then I messed with the timing a little. Sarted missing worse! I started to pull plugs and this is what I found. I have the Holley Street Avenger 570. Any help?


Thanks!
Mike.
907.863.3722

 

Really hard for me to see your picture. None of the plugs have blistered porcelain do they? It looks as if just the tip is slightly red? It also looks like there are deposits building up on the ground electrode. The slight red coloration could be the dye in the gasoline (shell used to be notorious for this). If that is correct, I'd guess about 20K miles on the plugs (any rounding of the center electrode?).

If that is the case and the inside metal portion of the threaded sleave has no color, except for a light grey ash looking deposit, I'd say you could probably go up a little on the main jets, and maybe an 1/16 to 1/8 turn richer on idle. And a fresh set of plugs.

When you are this close, the porcelain will tell you lean/rich under driving conditions. The inside of the threaded sleave will tell you idle condition. The perfect run would be a carmel color, to light brown on the porcelain (there will be a slightly darker line where the ground electrode shrouds the porcelain), and a medium dark grey on the metal threaded sleave portion.

With points, unless you go too rich on idle, you will get an intermittent "lean miss"(not a really accurate term, but one most people can identify with now-a-days). A good solid state voltage regulator will help a little, especially in tandem with electronic ignition.

 

Hi Scott and thanks for the reply. This miss is really getting to me. I pulled the plugs yesterday and they are looking really lean. That red spot you see on the porcelain is only on that side. The rest of the porcelain is barely pink, maybe a light salmon. The electrode is as seen. The inside of the threaded portion is black with a light build up of carbon. But, it just started missing yesterday and ran fine until then. Now, it misses really bad while driving. I don't think it's bad gas. Here is what I did to try and narrow it down.

- took a totally separate plug wire and tried it on every cylinder with no change.
- changed the cap and rotor again
- messed with the air fuel mixture
- checked all vacuum lines
- checked neg coil wire and found that it was loose. Tightened it up and miss still occurs
- cleaned battery terminals and posts
- checked the gap(changed the points yesterday). I did not change the condensor.

The only other options I have are, change the distributor(It looks new but I believe it to be reconditioned). I know, go electronic. That is my next project. Change my voltage regulator. And finally, if nothing else works, try another carb. The carb is a pretty darn near new Holly Street Avenger 570.

I don't believe any of my valves to be out of adjustment. I checked and readjusted them several weeks ago. Any other ideas? I wondering if it may be my voltage reg. I remember I ran into that same problem 20+ years ago with my 67.

 

I don't have one, but I have heard some guys complain about their Holley Street Avenger carbs. It seems they are very difficult if not impossible to dial in. I had a similar problem last summer, and Scott and I scratched our heads until we finally figured out it was bad gas. If you have let her set up for a long period of time, you might suspicion that, or there is water in the gas. Condensation forms in the tank if you don't keep it filled up when parked for a long time. If not, then make sure your fuel line filters are clean.

 

Soaring brings up a good point on the fuel.

Sounds like your idle mixture is rich and your jetting/powervalve is lean.

As for your miss. is it constant like one cylinder is not firing correctly, or is intermittent like a stumble at idle?

Since you changed the points you should change out the condensor as well. What did your orinial points look like? Also if you have any carbon buildup on the tips inside the distributor cap clean that, and lightly clean the carbon off the rotor tip.

Before replacing anything expensive, stop by a shop with a scope and have them through up the ignition pattern. That will tell you whats going on. Shouldn't be more than a 1 hour charge.

 

Well, it was my last guess. The carb! I figure it is the filter in the line that is part of the double pumper supply. I have a friend who loaned me a Edelbrock. I installed the carb and it runs without the miss. I get a little black smoke when I rev it. I can't adjust it out with the air mixute screws. This carb has sat for a while and I'm surprised it runs as good as it does. Even though I spent half the day yesterday, spent $46 on a vacuum gauge, $5 on a carb gasket, I really enjoy working on my Mustang. I really enjoy it even more when I troubleshoot and solve these problems. You guys were right with your last assumption, fuel problem.

 

Good job Mike!

The mixture screws only affect the idle circuit, so basically all you do with them is adjust for max idle speed (keeping your idle at or below 850 rpms with the idle speed screw). then leave 'em be.

The slight black smoke on acceleration could be an accelerator pump, or power enrichening circuit needing a little tweeking, or the secondaries maybe coming in a bit quick, or main jets slightly large, etc.

If you decide to mess with that stuff, only make one change at a time, and then right down in a note book exactly what you did, and the difference it made. Reset it to where it was and try something else. Repeat this procedure until you've gone through each circuit.
Take a break, then come back and read through everything you wrote. You should start to see a pattern that will help you make a mix-adjustment that will tweak it right to where you want it.

Keep this notebook, years from now it will jog your memory on what does what.

 

Sounds like expert advice.