Holley idling issues

[Wicked4659]

Hello all, I have a 500 ci (440 stroked) with a 950 Holley. I noticed the idle after a long drive, spikes to 1100 rpm in neutral, it is typically set at about 750 in neutral. This only happens when the car has been run for a long time. When the car cools down, the idle will go back to 750 rpm. Any thoughts?

 

[Ironracer]

Sounds like a sick *** ride! As in bad ***! Seriously, almost every one I've ever built does that when good and hot.

 

[pishta]

hot and higher fuel pressure? Does it have a functional bowl vent?

 

[Bewy]

That is a huge rpm increase. If it has 4 corner idle, I would try screwing [ seating ] the rear screws & just idle off the front screws.

 

[Ironracer]

Seems to me that all the old school DPs had 4 corner, and then they got cheaper in design, if I recall right?

 

[Oldmanmopar]

Idle off the secondaries with a four corner. square the primaries

If you have a conventional holley drill the primaries.

You can also open up the air bleeds. On the idle circuit. Go one size at a time with a drill bit if you do not have the removable style.

Making the air bleeds larger gives more air so it sucks less fuel. Its like drilling a hole in a straw. The larger the hole the less you get to suck from the bottom of the glass

 

[Oldiron440]

What type of carb spacer are you using?

 

[Wicked4659]

Sounds like a sick *** ride! As in bad ***! Seriously, almost every one I've ever built does that when good and hot.

It is a beast, I have to run street slicks as street tires won't hook up.

hot and higher fuel pressure? Does it have a functional bowl vent?

Fuel pressure is consistent, I haven't checked the bowl vent.

What type of carb spacer are you using?

None, carb is bolted directly to the manifold.

 

[MomsDuster]

Had something similar happen to me years ago. Turned out to be the mechanical advance sticking in the distributor.

 

[Oldiron440]

I’d make sure you don’t have a warped base plate.

 

[furyus2]

 

[OldmanRick]

When hot and the idle is at 1100 have you physically made sure the carb is on the throttle stop? Maybe if you're using a 4 hole gasket, it could be binding on the blades. Just a wild guess, but wouldn't hurt to check.

 

[Hysteric]

Hello all, I have a 500 ci (440 stroked) with a 950 Holley. I noticed the idle after a long drive, spikes to 1100 rpm in neutral, it is typically set at about 750 in neutral. This only happens when the car has been run for a long time. When the car cools down, the idle will go back to 750 rpm. Any thoughts?

Have you monitored the temperature difference between the 2?

 

[Mattax]

Seems to me that all the old school DPs had 4 corner, and then they got cheaper in design, if I recall right?

Other way generally. Most of the classic 4150 double pumpers were 2 adjustable idle mix screws. 4777, 4779 et al
Four corner is useful for engines with poor vacuum at idle. Four corner doubles the fuel available under the throttle blades which can be a big help with idle vacuum at say 8"Hg.

 

[canyncarvr]

Make sure your idle speed setting is a good ways AWAY from anything happening advance-wise in the distributor.

A bad example: Your idle gets you 6" of vacuum and your vacuum canister kicks in at 5".

Bad example #2: Your idle is set to 800rpm and your distributor mechanical starts at 900rpm.

Centrifugal start should be a good 3-400rpm away from idle...so I've been told by people that should know, anyway.

Also, as mentioned, check for slack in your throttle cable. I chased a hanging idle for a LONG time before I realized my cable was a tad snug. I had not changed anything that I remembered. Maybe I had reduced my idle on the carb and NOT checked the cable to make sure I didn't catch up with a bind? SOMEthing happened, and a too-tight throttle cable was the result.

That it 'used to be' good doesn't mean something simple is NOT the problem, some little change made maybe.

Good luck.