Carb Choke Adjustment?

DC3

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Lubbock Texas
My '73 has a Holley 650 double pumper with electric choke.

When cold starting, I turn the key to on, pump the accelerator once, then crank the engine which fires up immediately. The engine rpms begin climbing fairly quickly and will continue to climb until I blip the throttle at which point the engines settles in around 1500 rpm (if I did not blip the throttle the engine rpms would climb well past 3000). After sufficient warm up time, I blip the throttle again and the engine settles in at normal rpm.

Question: What is causing the engine to run past 1500 rpms on cold start which requires a throttle blip to settle in at 1500 rpms until warm? Is this a choke adjustment issue?

The engine runs fine otherwise and I have no other issues.

Thanks,

DC
 

DeeVeeEight

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Nov 3, 2008
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Southern New Jersey, USA
My '73 has a Holley 650 double pumper with electric choke.

When cold starting, I turn the key to on, pump the accelerator once, then crank the engine which fires up immediately. The engine rpms begin climbing fairly quickly and will continue to climb until I blip the throttle at which point the engines settles in around 1500 rpm (if I did not blip the throttle the engine rpms would climb well past 3000). After sufficient warm up time, I blip the throttle again and the engine settles in at normal rpm.

Question: What is causing the engine to run past 1500 rpms on cold start which requires a throttle blip to settle in at 1500 rpms until warm? Is this a choke adjustment issue? Yes.
The engine runs fine otherwise and I have no other issues.

Thanks,

DC

There is a stepped cam on the choke shaft, when cold it is at the maximum setting which results in the high RPM's. You can adjust the electric choke a bit if youu feel the RPM's are too high but from what you describe everything is working OK.
 

BBShark

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The rising RPM (beyond 1500) sounds kinda strange. When you blip the throttle before starting, does the choke cam change position while it's running?

You don't have a throttle control solenoid do you?
 

DC3

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Lubbock Texas
The rising RPM (beyond 1500) sounds kinda strange. When you blip the throttle before starting, does the choke cam change position while it's running?

You don't have a throttle control solenoid do you?

Strange to me too. I don't know if the choke cam is changing position while it is running. Will have to investigate. Once the rpms rise above 1500 and I blip the throttle, it settles in at 1500 and does not increase any further. I don't have a throttle control solenoid.

DC
 

SmokinBBC

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Mar 25, 2008
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Oak Ridge, NC
The rising RPM (beyond 1500) sounds kinda strange. When you blip the throttle before starting, does the choke cam change position while it's running?

You don't have a throttle control solenoid do you?

Strange to me too. I don't know if the choke cam is changing position while it is running. Will have to investigate. Once the rpms rise above 1500 and I blip the throttle, it settles in at 1500 and does not increase any further. I don't have a throttle control solenoid.

DC

No expert, but it sounds to me that you need to adjust your fast idle RPM's.

CHOKE ADJUSTMENT:
ELECTRIC CHOKE:
IMPORTANT: The Ultra Double Pumper carburetor has been factory wet-flowed and calibrated. The “out of the box” settings should be very close for all adjustments. The following tuning section is included ONLY to aid you in fine tuning adjustments.
1. You can control the choke operation by rotating the choke cap. If the choke comes off too soon, loosen the three screws and rotate the choke cap counterclockwise one notch at a time, until the choke operation is satisfactory. Rotate the choke cap clockwise, if the choke comes off too late. After making the final adjustments, start the engine and make sure the choke plate opens completely.
A. A choke that comes off too soon could exhibit one or more of the following symptoms: stalling, surging, backfiring, stumbles, or poor vehicle driveability when the vehicle is cold.
B. A choke that comes off too late could exhibit one or more of the following symptoms: black smoke from the tail pipe, poor driveability when cold, poor gas mileage, misses, or rough idle.
2. If choke operation is unsatisfactory and you have adjusted the choke cap in either direction to with unsatisfactory results, recheck your positive electrical line connection.
3. If the fast idle RPM is too low or too high for your preferences, TURN THE ENGINE OFF. Advance the throttle to wide-open, exposing the fast idle set screw below the choke housing (See Figure 7).
4. Using a 1/4” open end wrench, turn the screw clockwise to increase the RPM or counterclockwise to decrease the RPM. The factory setting should give you a 1500-1600 RPM fast idle speed.
NOTE: All vacuum ports must be plugged at this time.
Figure 7
5. Return the throttle to the fast idle position, as described in step 2. Restart the engine, and recheck the fast idle RPM. Repeat steps 2 & 3 until the desired fast idle RPM is met.
IDLE MIXTURE
 

DC3

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Lubbock Texas
The rising RPM (beyond 1500) sounds kinda strange. When you blip the throttle before starting, does the choke cam change position while it's running?

You don't have a throttle control solenoid do you?

Strange to me too. I don't know if the choke cam is changing position while it is running. Will have to investigate. Once the rpms rise above 1500 and I blip the throttle, it settles in at 1500 and does not increase any further. I don't have a throttle control solenoid.

DC

No expert, but it sounds to me that you need to adjust your fast idle RPM's.

The fast idle rpm is right on once I blip the throttle the first time. Something is causing the rpms to go past the set fast idle point before a throttle blip brings it back.

DC
 

Rod75

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Oct 22, 2009
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Just This Side of the Motorcity
Like DV8 stated, there's a stepped cam that the fast idle adj screw rests home on. When you stab the throttle before initial startup, this allows the choke spring to close the choke completely. This places the fast idle screw on the highest step, allowing RPM's above desired. When you blip the throttle after startup, incoming air will crack open the choke blade some, allowing the fast idle cam to decrease a step or two. Hence the decrease in RPM.
If your engine is in stock trim, I think the fast idle speed setting is around 1200 RPM. If your modded with cam, may need more.
 

DC3

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Lubbock Texas
If your engine is in stock trim, I think the fast idle speed setting is around 1200 RPM. If your modded with cam, may need more.

Thanks for the input. Engine is not stock. When I had it dyno tuned awhile back the tuner said fast idle needed to be 1500 RPM. This issue is not a big deal. I'm just more curious than anything. This engine setup is very similar to a '68 Chevy pickup I once had. Main difference is the truck had a Holley carb with vacuum secondaries. That one went straight to its fast idle setting and never went above. I'll be going to fuel injection before long anyway so chasing this issue is more of an education opportunity.

DC
 
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