Mysterious Carb Issue

[highcking]

The car: 1977 Mercury Marquis. The engine: 460. The carb: Holley 9040.

 

Problem: if the car sits a week or two, it will start and rev but will not idle. Do nothing but let it sit one day. Restart - runs and idles fine. Two weeks later the cycle will repeat. Won’t idle, wait a day, etc. I don’t drive this car often. But it always starts.

 

Question: what is happening and why does letting it sit a day if it won’t idle fix the problem (temporarily)? 

 

Bill

Luray, Va
 

 

[Rusty_OToole]

Sounds like the idle jets are getting plugged with dirt. Why they should clear themselves is a mystery. A good cleaning or overhaul may be in order or put on a rebuilt.

[highcking]

Rusty - it seems that way to me too. I can't think of a "self-clearing" mechanism. Yesterday, started fine but dies at idle within seconds. Today, started up and idled fine. Very weird. It's a very complicated Holley 4-barrel carb that I would not tackle rebuilding myself. It can be rebuilt or replaced, of course. O'Reilly carries the exact replacement for $400 +.

[Frank DuVal]

All my hot rod friends say the Holley is the easiest carburetor to rebuild of the 4 barrels. Of course they are not talking about a stock 1977 emission rated carb.....What are all those bolted on parts?😉

[highcking]

Absolutely right. The earliest versions of this carb for the 460 would not be that hard to do. But this carb itself is the complicated 1977 version. It's been an excellent performer but for this weird idle issue.

[Stude Light]

I was thinking it may be a component that dries out and shrinks, like a gasket or hose.  It may not even be in the carb but somewhere in the intake/vacuum side of the engine.  After you run the engine, get the fuel moving and it warms up, this part expands a little and starts to seal.  After two weeks it gradually dries out and shrinks.

Scott

[carbking]

The obvious solution is to start the car everyday

 

As to the Holley being easier to rebuild than other 4-barrels (Frank's comment)??? Familiarization makes anything easier.

 

I personally would rather do a boat load of Carters than 1 Holley; wonder how Cliff would vote on ease of the Holley vs a Q-Jet?

 

Jon.

[Str8-8-Dave]

If it won't come off fast idle I would be looking at the automatic choke mechanism which when the engine is cold should close and set the fast idle cam on the throttle.  As the choke opens the idle cam should step down until the choke comes completely off at which point the cam should have dropped out and the idle would be controlled by the throttle plate idle screw position.  Something is keeping that fast idle cam engaged.

[Frank DuVal]

3 hours ago, carbking said:

As to the Holley being easier to rebuild than other 4-barrels (Frank's comment)??? Familiarization makes anything easier.

 

Yes, to me the Quadrajet (and the older 4 Jet) are easier than the Holley. You should hear the "spirited" discussion between me and my hot rod/Holley friends! Of course, they like the 100s* of parts to change the carb to match whatever horsepower engine they are building, nothing stock for them.😉

 

I recently bought Cliff Ruggles book. A great read with lots of info.

 

* I exaggerate