Losing Idle Speed

[the_engineers]

I'm hoping someone can help on this.

When I start my 'Cuda, it struggles at idle, sounding like it's loading up.  Give it a little throttle and it gets out ahead of it and sounds fine.  After it clears, it really smooths out but then starts to lose idle speed.  If I hold the pedal at 2000 rpm and then let off, it'll drop to 1500 and then drift down to 1000, 500 and flatlines in a matter of 1-2 minutes.  Also the motor smells extremely rich and the plugs are pretty dark.

The engine is a 360 with a Voodoo cam, Edelbrock heads and RPM AG intake and a Holley 750.  I've rejetted to 68's on the primary side and am running a 3.5" power valve.

A few more pieces of information:
1. The Summit fuel pump I have originally put out 14 psi, even with the Summit regulator turned all the way down.  I've got a Holley regulator and it's down to 8 psi right now.  I've got plans for a Mallory 110 and new needles/seat assemblies within the next week, figuring the pump may have hurt the original needles/seats.
2. Vacuum gauge reads around 10", but flutters at least 2-3" at idle.  It's hooked to ported vacuum in the carb base.
3. The fuel level is set at the bottom of the sight plugs.
4. Manual brakes, so there is no booster to leak.

What kind of vacuum should I expect to pull?  The motor is built around a 425-440 hp recipe.

[Chryco Psycho]

- well you have a # of problems , first you need to change to a 1" or 2.5" power valve to keep it closed . that will clean up the rich idle & flooding down , the power valve is open if you have only 2-3" of vacuum at idle so you need to be lower than that reading to stay closed
- second the vacuum advance hooks to the metering block on the side of the carb on most Holleys but the newer ones are on the base so I hope you have it connected properly
 you may need to drill a small hole 1/16" or os in the throttle plates on the primary side so thay can be closed slightly to allow better pull from the idle circuit , you can also insert a small piece of wire in the idle circuit idle bleeds , I usually insert a piece of mig wire .035 thick or so
 if the carb is not flooding the needles are good

[the_engineers]

- well you have a # of problems , first you need to change to a 1" or 2.5" power valve to keep it closed . that will clean up the rich idle & flooding down , the power valve is open if you have only 2-3" of vacuum at idle so you need to be lower than that reading to stay closed
- second the vacuum advance hooks to the metering block on the side of the carb on most Holleys but the newer ones are on the base so I hope you have it connected properly
 you may need to drill a small hole 1/16" or os in the throttle plates on the primary side so thay can be closed slightly to allow better pull from the idle circuit , you can also insert a small piece of wire in the idle circuit idle bleeds , I usually insert a piece of mig wire .035 thick or so
 if the carb is not flooding the needles are good

Let me clarify.  The idle vacuum fluctates between a low of 7"-8" and a high of 12-15".

[miketyler]

Funny - mine behaves the same way. Its all-stock 340 small block with 780 Street Avenger carb.  Starts right up cold but you have to keep your foot in it or else rpms drop to flat line within seconds. I need to to put a vacuum gauge on it and see what is going on

[Chryco Psycho]

Which Holley ? does it have a choke on it ? or is it a HP series ?

[the_engineers]

Which Holley ? does it have a choke on it ? or is it a HP series ?

It's the new version of the 750, the 80508s.  Vacuum secondaries, electric choke, which I currently do not have hooked up.

[MEK-Dangerfield]

It's the new version of the 750, the 80508s.  Vacuum secondaries, electric choke, which I currently do not have hooked up.

If you don't have an electric choke hooked up to power, the choke plate will stay shut. I hope you mean you removed the choke plate.   


  Mike

[the_engineers]

The choke opens under throttle, but supplying it with power is definitely on the to-do list for the near future.

[Chryco Psycho]

either way that is the issue , if the choke is not comiing on it will run lean & stall out , if the choke is coming on it will nto open fast enough without power causing it to run too rich & stall out as it warms up . Connect the choke into the blue 12v switched wire either at the voltage regulator or alternator field , or the ballast resister