DCDoug, we have pretty much the same engines, the exact same carbs (Holley 4160/Vac Secondaries), and we use the same gasoline -- so this is going to happen to you, it's just a matter of time. I've actually been waiting for it to happen, but when it did, even I was taken aback by the swiftness and ferocity at which it attacked my engine's performance. I'm talking about the
Holley Zinc/Ethanol Clog and it's been all over the car forums for quite some time. Do you remember a couple of weeks ago I wrote that I had taken a long, slow speed, drive? The car and engine behaved beautifully. It then sat in the garage for a week or so, untouched. When I then started it up it ran horribly rough and would not even hold an idle. I mean it was bad. BAD, BAD, BAD – I mean,
BAD. The only way I could keep it running was by tapping the throttle (thus having the accelerator pump squirt). I was stumped -- how can a car run beautifully right before you turn it off, and than run horribly when you start it up? I figured the low speed drive had fouled the plugs, so I pulled them. Sure enough, they were covered in black carbon... so I replace them. And WTF, might as well replace the MSD cap and rotor too (which looked a little bad as well), remembering to bend the rotor prong up a little bit. Well, at the speed I work that took about two days... and had no effect whatsoever on the problem. Still exactly the same -- bad stumbling, rough, can't hold an idle, pathetic and undrivable. Then I start thinking "out of the box" with stuff like Lykin's
"you've wiped a lobe -- in fact Pat, you've wiped 8 lobes all at once even with the car not running -- see, I told you so." Or maybe the coil went bad, or maybe the MSD box has an intermittent fault, or I developed a monster vacuum leak through the manifold gasket overnight, etc. Well, I figure the likelihood of all that is small, and If I rev the engine hard, it sounds pretty good and strong if you can just get out of the idle circuit... so it must be the
Holley Zinc/Ethanol Clog. How the heck does a carb clog up just sitting for a week in the garage? I don't know, but it does. And I've heard rumors that the amount of ethanol that is in our gas is wayyy higher than the 10% or 15% that is claimed. Evidently that ethanol combines with the
zinc in the Holley carbs to make a wonderful clog that can appear literally out of nowhere. It will happen to you sooner or later, so here's how you clear it out without having to pull your carb off the manifold. BTW, the secondaries on our 4160 carbs have an idle circuit as well (mostly to keep the gas fresh in the bowl), but you just can't adjust it -- you still have to clean it out though. If you look down the top of your carb you will see your air bleeds (two per barrel, eight in total) outside are idle, inside are main. Blast carb cleaner down the bleeds and then follow it up with a blast of compressed air down through them to clear them all out. It's a very simple fix, but you can spend a lot of time chasing it down. Our 4160s idle rich to begin with. But when they're clogged and you keep using the squirter to dump gas on them you can carbon up your plugs pretty quickly and then you start thinking it's electrical, etc. So, when you go out one morning and start your car up and it runs so bad that you literally can’t believe it, clean your bleeds before you do anything else. Anyway, that's your handy "tip for the day." Here's two shots of me blowing out the air bleeds just so you know what they are:
