Sudden Holley Problem

[CCCC]

I do not know much at all about Holley carbs - and do not often drive this 68 Suburban SB 327 with a double bowl Holley - but do start/run it regularly and it has never blinked. Today it started fine, but will not settle down and run at idle. Electric choke operates as it should and the engine runs great above about 1,000 to 1,400 RPM but simply dies when the foot comes off the pedal and RPMs drop.

I have tried tapping on the bowls to un-stick any needle valve problem (no effect) and tomorrow will run in Seafoam or something else good toward a clean-out and see what happens, But, even in my Holley ignorance, i am thinking that some internal component has failed because the die-out is so abrupt and this came on so suddenly.

Will appreciate experienced insight on this - am moving to new location and need to have this thing running right.

[RustyBucket]

... sounds like the dread little flake of trash in the needle & seat on the front or rear float bowl. Easily cleaned or replaced. Tapping or Seafoam probably won't clear it. Start it & look down in the carb.. You'll probably see fuel dribbling either in the front or rear venturi. Holley's aren't complex, small parts are cheap & there's lots of info & video about working on them. They don't have sudden terminal internal failures very often.

[KQQL IT]

Check for a vacuum leak.

Had a vacuum leak at the modulator on my th400 caused all kinds of havoc

[geezer#99]

Everybody always blames the carb!
First thing I check is distributor.
Initial timing first followed by slow rpm increase to see if timing increases. Tells me if weights and springs are ok. Vac advance plugged off of course.
Then I check plug wires are all secure.
Then if all checks out whip out the megaphone to listen for vac leaks. Megaphone is a small funnel stuck into a 3/8 inch fuel line.
Then it’s on to the carb. Pop the level plugs out to check float level. Listen in the primaries for slight crackling. A weepy booster can make small fuel droplets make a cracklingnoise as the droplet sneaks past the blades.

[70']

You mentioned not driving it very often. If that's the case never put ethanol fuel in it, and always add Stabil when you add fuel to the tank. My guess is, Ethanol fuel turned to varnish in the carb. Sea Foam would be the best fix for that, but its going to take some time to work.

[CCCC]

Thanks for the helpful thoughts to date. Have not let it sit with ethanol in it - did have to cure the effects of that in a couple of others. I had checked for vac leaks at the dist and brake booster lines - no other connections on this one - and will do a thorough check around the base/manifold with the noted "megaphone" method once I get it to new location. Although this HEI dist setup has been very dependable and no reason to suspect slippage, I will check timing/etc. as well. Meanwhile, running some Seafoam in and letting it sit did help quite a bit and it does idle down enough to make it comfortable to load onto a trailer later this morning. But, idle is still not low and smooth and had to set that RPM stop up a bit. Still am thinking that something internal may need a look-see. Thanks for you interest and help - will report findings.outcome when done.

[fdbdw]

I had the same issue once, I had a piece of dirt ( or something) clogging the idle circuit. Pulled the idle screws out and and gave it a couple quick bursts of compressed air to clear the debris, problem solved. If you do this you will most likely get a little fuel spray out of the carb so take all the necessary safety measures. It’s either a quick fix or a quick problem elimination.

[CCCC]

Finally got into this Holley and fixed it - the problem was a leak in the diaphragm of what commonly is called the "power valve" which is in the metering block between the front fuel bowl and the main carb body. Actually, in my thinking, it should be called the "idling" valve due to its function. Actually installed a full rebuild kit due to relative cost of that vs. just the valve, and because there was a good bit of oxidation crud in there due to ethanol effects on the tank/lines. Engine now idles fine and carb working quite well, especially after some close adjustment of the instant action accel pump. Thanks for all replies.

But - this kit brought in a new issue. Will post a question on that one.