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accelerator pump - holley 4160 or 4150

IH2LOSE

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Stumble,stall,bog on acceleration

You should be able to just adjust the slack out of it.
 

IH2LOSE

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Same symptoms

I share what I know of the pumps need

at idle the car uses the idle circuit.

once your off the idle circuit and the throttle plates are open if the motor does not have enough vacuum there is no way for the gas to get into the motor

the pump gives a quick squirt till the vacuum catches up to pull the gas in

car in park or neutral (No load) race the motor and you get no stumble you could still have enough vacuum to make you believe you dont have a problem with fuel

Car in gear race the motor (under load) this is the real test as if you have the stumble it could be the pump, or undersized squirters, or clogged squirters

What actually happening with the car?
 

IH2LOSE

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hey last thing

there is a cam that activates an arm that presses on the pump

is the cam worn or a wrong cam

is the arm bent make sure the arm is up against the cam then move the throttle and make sure the arm is riding on the cam while your seeing what the clearance is on the pump I think the slack is .020 on a holley.

Also make sure nothing is interfeering with the pump when the air cleaner is installed on the car
 

brumbach

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Middleboro, KY
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1965 convertible
Same symptoms

I share what I know of the pumps need

at idle the car uses the idle circuit.

once your off the idle circuit and the throttle plates are open if the motor does not have enough vacuum there is no way for the gas to get into the motor

the pump gives a quick squirt till the vacuum catches up to pull the gas in

car in park or neutral (No load) race the motor and you get no stumble you could still have enough vacuum to make you believe you dont have a problem with fuel

Car in gear race the motor (under load) this is the real test as if you have the stumble it could be the pump, or undersized squirters, or clogged squirters

What actually happening with the car?

I recently rebuilt the carb. I adjusted the accelerator pump as per directions but car is acting as you describe. I must have slack. I'll tinker a bit and see if it doesn't clear up. Thanks for the education and assistance. Bill
 
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'67 Marina Blue Convertible
The only issue I ever see is accelerator pumps that are improperly adjusted; the .015" clearance adjustment is made with the throttle lever at WIDE-OPEN THROTTLE position, and with the pump operating arm depressed. Takes three hands or a good rubber band, but it MUST be done that way.

:beer
 

brumbach

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1965 convertible
The only issue I ever see is accelerator pumps that are improperly adjusted; the .015" clearance adjustment is made with the throttle lever at WIDE-OPEN THROTTLE position, and with the pump operating arm depressed. Takes three hands or a good rubber band, but it MUST be done that way.

:beer
Well to the best of my abiliities, I've done just as you say but it continues to stumble at the higher rpm range. I'm about to take the carb apart again and examine the the pump. Might even put the old one back in since I didn't have this particular problem before the rebuild.
 

IH2LOSE

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Well to the best of my abiliities, I've done just as you say but it continues to stumble at the higher rpm range. I'm about to take the carb apart again and examine the the pump. Might even put the old one back in since I didn't have this particular problem before the rebuild.

I hope I can explain this correct

When you say high RPMS the pump only gets you towards higher rpms when you hit the gas.

Once your at high rpms and you have a miss, its not from the pump.The pump is only used to get you toward higher rpms.

Once you have flow thru the carb (air) then the air/vacum takes over on pulling the fuel into the motor.

How is the ignition system on the car,
 
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Brumbach,

Like IH2Lose said, your pump cam could need replacement with a different cam profile; however, not knowing what the problem is on your Vette is troubleshooting this issue back-wards.

You see, for sag or hesitation during light acceleration, one must look at the following:

- Intake [manifold] leaks

- bad fuel

- clogged air bleeds or passages [perhaps not likely at all since you just
completely rebuilt the carb]

- leaky or disconnected distributor vacuum advance line

- wrong initial timing setting

- acceleration pump defective [ perhaps, as I stated above, the pump cam is probably not the best profile for your engine settings right now (i.e. the cam, CR, timing settings)

- clogged idle transfer slots/ holes (you did clean all of the parts...right?]

- if after all of the above items check-out fine, then perhaps you have too-large of a carb for your engine.

Returning to the cam profile, one must understand that the pump shot on Holleys is needed to help the engine go from the idle system to the main system (there are other purposes as well), so the cam profile can be changed to adjust how soon or how late the shot is delivered. Too soon, and you won't have fuel to sustain the acceleration of air through the venturi. This will result on a lean condition, and a backfire will develop. Deliver the shot late, and you'll feel hesitation or a lag in acceleration.

GerryLP:cool

p.s. I forgot to mention that the pump cam profiles also adjust the amount of fuel is delivered for that particular cam.
 

brumbach

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Mar 6, 2004
Messages
330
Location
Middleboro, KY
Corvette
1965 convertible
I hope I can explain this correct

When you say high RPMS the pump only gets you towards higher rpms when you hit the gas.

Once your at high rpms and you have a miss, its not from the pump.The pump is only used to get you toward higher rpms.

Once you have flow thru the carb (air) then the air/vacum takes over on pulling the fuel into the motor.

How is the ignition system on the car,
It stumbles or pauses when I hit the gas from a stop or rolling stop. Seems to run okay from there until I really step on it when cruising at 55 mph. I've checked the timing, changed the spark plugs and plug wires, and adjusted the floats. I suppose I could change the points and condensor next.

The car was running fine until last weekend when it just all of a sudden backfired. I rebuilt the carb two years ago and again after this recent back fire. Assumed I probably blew the power valve.
 

brumbach

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Mar 6, 2004
Messages
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Middleboro, KY
Corvette
1965 convertible
Brumbach,

Like IH2Lose said, your pump cam could need replacement with a different cam profile; however, not knowing what the problem is on your Vette is troubleshooting this issue back-wards.

You see, for sag or hesitation during light acceleration, one must look at the following:

- Intake [manifold] leaks

- bad fuel

- clogged air bleeds or passages [perhaps not likely at all since you just
completely rebuilt the carb]

- leaky or disconnected distributor vacuum advance line

- wrong initial timing setting

- acceleration pump defective [ perhaps, as I stated above, the pump cam is probably not the best profile for your engine settings right now (i.e. the cam, CR, timing settings)

- clogged idle transfer slots/ holes (you did clean all of the parts...right?]

- if after all of the above items check-out fine, then perhaps you have too-large of a carb for your engine.

Returning to the cam profile, one must understand that the pump shot on Holleys is needed to help the engine go from the idle system to the main system (there are other purposes as well), so the cam profile can be changed to adjust how soon or how late the shot is delivered. Too soon, and you won't have fuel to sustain the acceleration of air through the venturi. This will result on a lean condition, and a backfire will develop. Deliver the shot late, and you'll feel hesitation or a lag in acceleration.

GerryLP:cool

p.s. I forgot to mention that the pump cam profiles also adjust the amount of fuel is delivered for that particular cam.
I just returned from a 10 minute drive. Here's a better description of what's happening.

When I pull out the car stumbles as though the gas supply is interrupted. As I go through the gears, the car has a slight miss until I level off on the acceleration then it runs fine. If I floor the pedal, it misses real badly.

My distributor is a mechanical advance not vacuum.

My timing is set a 9 BTDC. I've had it at 8 and 10 BTDC but the car has always performed best at 9.
 

brumbach

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Middleboro, KY
Corvette
1965 convertible
Well the problem is solved. Don't know what fixed the problem but I did the following and no longer have the problem.

1. Changed the inline fuel filter.
2. Tank was about half full so I topped it off.
3. Pulled the carb and adjusted the accelerator pump on the bench and reinstalled the carb.
4. Changed the gasket between the carb and the intake manifold.

Whatever the problem is now behind me. Thanks so much for the advise.

Bill
 

brumbach

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Middleboro, KY
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1965 convertible
For anyone interested...

My 65 is running great after several weeks of fixing this or fixing that. I've rebuilt the carb, adjusted the accelerator pump at least three times, and changed the fuel filter twice. I considered replacing the fuel pump and flushing the gas tank before someone suggested that it may not be a fuel matter but instead electrical. So I launched into the points, plugs, plugs wires, coil, condensor, dist cap, rotor, and dwell and timing. It definitely was a fire issue! Somewhere in my replacement of electrical things, she returned to life and runs great. At first, I really felt dumb about it all but my research leads me to believe, for the novice, the misdiagnostics between electrical and fuel is rather common. Hope my "oops" helps other beginners.

Bill
 

Kid_Again

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Jul 6, 2004
Messages
1,171
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NJ - Which exit you from?
Corvette
65 SB Roadster, 66 BB Coupe
The only issue I ever see is accelerator pumps that are improperly adjusted; the .015" clearance adjustment is made with the throttle lever at WIDE-OPEN THROTTLE position, and with the pump operating arm depressed. Takes three hands or a good rubber band, but it MUST be done that way.

:beer



i didn't know that!!!;worship
 

Tom Bryant

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1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
These things can be diufficult to isolate. Glad you found the problem.

Tom
 

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