Inconsistent idle after Edelbrock 1405 rebuild

Been a long time since I've had to ask a real question but here goes. I'm stumped.

I recently rebuilt my Edelbrock 1405 carburetor and followed all the instructions. The car was running ok before the rebuild, but it had been a few years since the last one and it was time for a cleaning.

With the rebuild done I got to work adjusting the idle mixture screws and idle speed.

After I reached a point where I was happy with that, the engine still wasn't running right. If I go hands off and just listen the idle will speed up and then slow down (almost to stalling) all on it's own at pretty regular intervals. 5-10 seconds fast, 5-10 seconds slow. I am able to keep it running but only by adjusting the throttle screw so it gets more gas/rpm at idle.

The only other change I made was to replace the fuel filter. Everything else is exactly the same, and was working fine before I rebuilt the carb.

Any ideas?

Sure sounds like a vacuum leak. Maybe when removing/installing an older hose you inadvertently caused a break/crack.

Get some spray carb cleaner and spray it around the carb and hoses to see if there is a vacuum leak.

You can also use brake clean or starting fluid.

Mel

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Checked for a vacuum leak but everything looks ok. Hoses are good, no leaks at the carb to spacer or spacer to block seals.

I DID re-check my floats and they were way off. I'm hoping the inconsistent idle is related to that. After listening a little further, I noticed that if I let the idle go low enough, the engine slows down and eventually stalls. Almost like it's running out of fuel. This makes the float's being off seem like the problem. I'll try again this weekend. Thanks for the suggestions!

Got a chance to do some more work/testing today. After adjusting the floats to precisely match the rebuild specs the problem persists.

If I let the idle go too low, it starves out and stalls. I can keep it running if I turn the idle screw in and keep the rpms higher. But even then the rpm bounces all over. Up, down, and back up.

I took it out around the block and, while it technically ran, it was surging all over the place.

I've looked everywhere for vacuum leaks but didn't see any, so I'm thinking I must have made some kind of mistake during the rebuild. I'm tempted to get another rebuild kit and try again.

Not sure where to go with it yet.

If this is on the stock Ford intake, then it is probably the carb-to-intake interface. You'll need a carb spacer and very good gaskets. Edelbrock carbs and Ford intakes don't seem to like each other, producing vacuum leaks.

It's on an Edelbrock intake, but I did notice a chip at the bottom of the plastic spacer where it connects to the intake. It doesn't seem to be the problem, but I might get an aluminum spacer and new gaskets just to be safe. Thanks for the suggestion.

another nod towards a vacuum leak as others have stated, your symptoms are very typical for a vac leak...

Hmm, ok thanks. Maybe the carb isn't seated properly or has a bad gasket. I have a new spacer, gaskets and rebuild kit on the way. We'll try this again and I'll let you guys know what happens.