Carb problem - Team Camaro Tech
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post #1 of 11 (permalink) Old Jun 14th, 14, 05:31 PM Thread Starter
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Mike
 
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Carb problem

Having a little problem with my holley hp carb its a 750 has a bad hesitation or bog off idle to wide open throttle im using an lm1 afr meter and I noticed that when on the initial hit it goes crazy lean like 26.3 currently I have 31 squirters in it front and back I have tried 35 with no change even tried changing pump cams to no avail any help at all appreciated if you need more engine info I can give you that also


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post #2 of 11 (permalink) Old Jun 14th, 14, 08:43 PM
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Randy
 
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Re: Carb problem

What are the timing specs? make sure the acc pump spring and arm are adjusted correctly. also make sure the adjusting nut on top of pump spring is not lifting off of pump arm.

1967 camaro, 327, 9.7 CR, comp cam xs274solid, vortec cylinder heads, edelbrock vortec performer rpm, 750 annular carb, HVH 2" spacer, msd pro billet w/6A box, turbo 350 trans, 3500 stall, 4:10 gears, caltracs suspension, m/t drag radials.
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post #3 of 11 (permalink) Old Jun 15th, 14, 01:20 AM
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Chris
 
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Re: Carb problem

Questions: Is this a new carb or is it a used carb that you purchased? How long has it been running on this particular motor? Has it always had this problem or did it just start to have this problem.

Have you played with the distributor springs and or weights or put in a new distributor prior to problem occuring? Have you taken a vacuum reading and have you checked for vacuum leaks around base of carb, manifold, and vacume lines? If not i would do so before you start messing further with the carb.

Assuming your test shows no vacuum leaks and the distributor was not messed with and your timing is set correctly than i would pull the carb and check that it is setup properly especially if you purchased it used and previous owners messed with it. You may want to take this opportunity to get a carb kit and rebuild it so you know the condition of the carb inside and out.

I would make sure that the carb is set up to its stock configuration! That means if i am not mistaken that the jet sizes are 73's front and rear. (rears could go a couple jet sizes richer if need be) 73's for the primaries are great for the 355.

The squirters and pump cams are not the issue here. The squirter size stock is 31's and again is ample for your 355ci motor. Put the stock accel pump cam back in the #1 position and put back the 31's squirters.

power valve 6.5 stock and what you want for your application.

The 750 holley have had issues with the arm that is supposed to sit on the pump cam but when you look closely it is riding in the spring and not on the pump cam! This is the first thing to check with the carb off the motor on the bench.

1)Visually look at the arm and open and close the throttle while watching the actuating arm that is supposed to ride on the accel pump cam. Many times you will find that it is sitting/resting partially on the spring. The fix is to remove the actuating arm and bend the arm over so it rides on the cam.

2)You should also check that the accel pump arm is setup and does not have "excessive" play. Slowly move the throttle open and watch it make contact with the accel pump arm lever. It should make contact with the accel pump arm the moment you start to move the throttle. Many times this is just not the case and there is too much play. required by tightening the spring so that it is just touching the accel pump arm. Note: You also need to make sure that when the throttle is fully open you can fit a .20 feeler gauge between the arm and the spring pad.

3) Next is to check your primary butterfly's setup. looking from the bottom of the carb up note the amount of transfer slot that is exposed without touching the throttle linkage. The amount exposed should resemble a square. Taking a .20 feeler gauge and holding it against the throttle plate and side wall should just about cover the square gap you are after.

4) The secondaries also need to be setup properly. Holding the carb up to a light look at the secondary throttles bores and adjust the butterfly's to allow the same amount of light to show through as the primaries do now that you set them. ( The Very Small, adjustment screw for the secondaries is under the carb base plate on drivers side).

5) make sure that your float levels are set correctly!

These are the first issues to overcome or your carb will never run properly until they are adjusted correctly.

67 RSSS Van Nuys, 4th week Sept,1966
ps,tilt,headrest,spd warn,pw,am/fm,delux int,
remote mirror,rear defrost,tint glass.etc...
TKO 600 Extreme,12bolt 3:73 gears.
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post #4 of 11 (permalink) Old Jun 15th, 14, 07:47 AM
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Mike
 
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Re: Carb problem

Buy this book and read chapter 5 and 6. It will provide a step by step procedure on how to setup your carb. "How to build and power tune Holley Carburetors". The ISBN number is 1-903706-61-0 You can also go to the publishers website. www.velocebooks.com

Good luck
Mike
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post #5 of 11 (permalink) Old Jun 15th, 14, 08:26 AM
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Mark
 
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Re: Carb problem

Check your power valves and your .015 accel pump at WOT fit. Also the rear flap adjustment.




Back off adjustment screw until the throttle plates are fully closed (secondaries). Turn adjustment screw until it just touches the throttle lever and turn 1/2 turn more to position the valves.


Suck on this and see if if holds air with your tongue.

Mark 70 Z28 M22 3.73 Z21 Z87 - Lunati 20120121 Roller Cam

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post #6 of 11 (permalink) Old Jun 15th, 14, 01:43 PM Thread Starter
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Mike
 
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Re: Carb problem

Quote:
Originally Posted by 67RSSS View Post
Questions: Is this a new carb or is it a used carb that you purchased? How long has it been running on this particular motor? Has it always had this problem or did it just start to have this problem.

Have you played with the distributor springs and or weights or put in a new distributor prior to problem occuring? Have you taken a vacuum reading and have you checked for vacuum leaks around base of carb, manifold, and vacume lines? If not i would do so before you start messing further with the carb.

Assuming your test shows no vacuum leaks and the distributor was not messed with and your timing is set correctly than i would pull the carb and check that it is setup properly especially if you purchased it used and previous owners messed with it. You may want to take this opportunity to get a carb kit and rebuild it so you know the condition of the carb inside and out.

I would make sure that the carb is set up to its stock configuration! That means if i am not mistaken that the jet sizes are 73's front and rear. (rears could go a couple jet sizes richer if need be) 73's for the primaries are great for the 355.

The squirters and pump cams are not the issue here. The squirter size stock is 31's and again is ample for your 355ci motor. Put the stock accel pump cam back in the #1 position and put back the 31's squirters.

power valve 6.5 stock and what you want for your application.

The 750 holley have had issues with the arm that is supposed to sit on the pump cam but when you look closely it is riding in the spring and not on the pump cam! This is the first thing to check with the carb off the motor on the bench.

1)Visually look at the arm and open and close the throttle while watching the actuating arm that is supposed to ride on the accel pump cam. Many times you will find that it is sitting/resting partially on the spring. The fix is to remove the actuating arm and bend the arm over so it rides on the cam.

2)You should also check that the accel pump arm is setup and does not have "excessive" play. Slowly move the throttle open and watch it make contact with the accel pump arm lever. It should make contact with the accel pump arm the moment you start to move the throttle. Many times this is just not the case and there is too much play. required by tightening the spring so that it is just touching the accel pump arm. Note: You also need to make sure that when the throttle is fully open you can fit a .20 feeler gauge between the arm and the spring pad.

3) Next is to check your primary butterfly's setup. looking from the bottom of the carb up note the amount of transfer slot that is exposed without touching the throttle linkage. The amount exposed should resemble a square. Taking a .20 feeler gauge and holding it against the throttle plate and side wall should just about cover the square gap you are after.

4) The secondaries also need to be setup properly. Holding the carb up to a light look at the secondary throttles bores and adjust the butterfly's to allow the same amount of light to show through as the primaries do now that you set them. ( The Very Small, adjustment screw for the secondaries is under the carb base plate on drivers side).

5) make sure that your float levels are set correctly!

These are the first issues to overcome or your carb will never run properly until they are adjusted correctly.

Ok tried everything listed here even installed new 6.5 power valve I had 31 squirters front and back accel pump arm is .015" installed new diaphragm and spring in the primary still stumbled bad changed to 37 squirters front and back and used the hollow screws and it got better but not all of the stumble is gone I know I should never need a squirter this big but what else could be the problem?Seems to me its a lean stumble.


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post #7 of 11 (permalink) Old Jun 15th, 14, 02:35 PM
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Randy
 
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Re: Carb problem

did you see if the adjusting nut was lifting off the arm? sometimes smaller squirters will help, like number 28, you want to use all the fuel out of each pump shot.

1967 camaro, 327, 9.7 CR, comp cam xs274solid, vortec cylinder heads, edelbrock vortec performer rpm, 750 annular carb, HVH 2" spacer, msd pro billet w/6A box, turbo 350 trans, 3500 stall, 4:10 gears, caltracs suspension, m/t drag radials.
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post #8 of 11 (permalink) Old Jun 15th, 14, 05:26 PM Thread Starter
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Mike
 
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Re: Carb problem

Changed pump cam to the #2 position hole stumble gone also switched back to the 31 squirters thanks everybody for your help


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post #9 of 11 (permalink) Old Jun 15th, 14, 07:14 PM
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Chris
 
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Re: Carb problem

Good to hear. Which color cam are you using Mike.

67 RSSS Van Nuys, 4th week Sept,1966
ps,tilt,headrest,spd warn,pw,am/fm,delux int,
remote mirror,rear defrost,tint glass.etc...
TKO 600 Extreme,12bolt 3:73 gears.
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post #10 of 11 (permalink) Old Jun 15th, 14, 07:28 PM Thread Starter
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Mike
 
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Re: Carb problem

Quote:
Originally Posted by 67RSSS View Post
Good to hear. Which color cam are you using Mike.


I'm using the pink cam in the primary and secondary


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post #11 of 11 (permalink) Old Jun 15th, 14, 08:52 PM
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Mike
 
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Re: Carb problem

The book I suggested you purchase will tell you what moving the cam did. I am glad you figured out the stumble.

Enjoy the ride
Mike
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