As my other post stated, I installed a holley-500cfm. Installed #62 jets.
I can't get her to idle lower than 900, or set the idle mix screws. (in or out, doesn't change anything.) I'll preset the timing to 12 btc, screw the mix screws 2 turns out. As I idle her down at the idle screw, she will die @ 900 r's.?
I do not have any vac leaks. I can slowly close hand over throat of carb and she will die without any increase of throttle. I've have been taught this way to check, and it always works.
Can't think of anything else.

Robert P.

 

Please add any Updated info to the Original post instead of starting another.
This practice is confusing and causes other user's who were trying to follow along to help have to Jump all over the place looking for the next part.

Plus, The thread ends Up getting merged by a Mod or adminstration.

I sent a Private message explaining this already.

This thread will be now merged to the original.

 

To me it sounds like an internal problem.
You may have to tear it all down, dip it, and use compressed air to blow out all of the carb passages (safety glasses recommended).

----Patrick

 

Hey Patrick, do you have a camera set up under my hood?
That's what it was. Essentially; there where two problems. (1) dirt was clogged up in the block section of the passenger side mix screw passages. Thank you Dennis; I sprayed each passage with carb cleaner; noticing that one side would spray through, but the other would not. Blew in compressed air. Wahlah. It's amazing what 80#'s of compressed air can push out.
(2) After taking the carb apart, I paid close attention to the idle vac port in the venturi throat in relation to the throttle plates, @ idle(plates closed). The port was below the plate but, there was a slice cut just above the vac port about a 1/4" long. Hummm. If air was trying to pull through the hole below the plate it would enter through this slit above the plate, being that the vac hole and this sliver where attamolded into the idle passage in the block. So, I got out my trusty JB Weld and covered the slits. Now air would have to travel from the idle vac port below the t-plate, through the passages. Which just happens to pass the fuel-mix screws.
Cranked her up. Idled beauuutifully. A few mix adjustments. Dropped idle down to 650. She's purrin like a kitten. No more poppy noise out of the carb.

If you can't fix it the first time, keep trying. Knowledge is a wonderful thing.

Thanks for all the replies on this one. Even the slightest little suggestion can trigger a thought in the mind of the one who is thinking.

Robert P.

 

I was thinking about the reasons why I've had to tear apart my 780, and that was it. DIRT. Sometimes I just don't pay enough attention to my fuel guage and some crap gets past the filter (because I don't pay attention to that either).
Well, you'd figure by now I'd have learned to keep a better eye on things after tearing apart 4 times.
We'll see......LOL

----Patrick

 

Use to run a Holley 500 on my 390. Despite having a gas filter in front of elect fuel pump, and 1 under the hood, a couple of times it would get a speck of foreign material in there and cause a rough idle/stumble. Great carb if you like 2bbls!

 

I am assuming that this is a holley #4412. If so, that carb should have had 73 jets in it, not 52s. As far as the power valve goes, you are in the ballpark because they originally come with a #50 valve.