I have a 350 mild short block, 461 casting camel hump heads, Comp Thumper (.050" lift=227 Intake and 241 exhaust) Holley Street Avenger 670 (elec Choke), Muncie M20, 3:42 Eaton. I'm getting major hesitation on acceleration right out of the gate on just a normal take-off. I will check the float level tonight. Vacuum is 10" (fyi...power brakes work great). Carb is stock....no mods, 6.5 PV. What else should I attempt to adjust and how? Thanks

Hi Gary,
Check this thread:

http://www.camaros.net/forums/showthread.php?t=162589

Hope this helps.

I have been told with my Holley, that will happen if the power valve is bad or is'nt ajusted right. Power valve should have an arm that conects to the throtle and the slightest movement of the throtle should result in movement of the power valve arm/spring. If no movement you can adjust by the nut on top of the power valve arm on the front driver side of the carb. But I am an ameture so I could very well be wrong and giving poor advice...lol....just figured I would try to help as I have gotten alot of help from this site.

Kage79

I have been told with my Holley, that will happen if the power valve is bad or is'nt ajusted right. Power valve should have an arm that conects to the throtle and the slightest movement of the throtle should result in movement of the power valve arm/spring. If no movement you can adjust by the nut on top of the power valve arm on the front driver side of the carb. But I am an ameture so I could very well be wrong and giving poor advice...lol....just figured I would try to help as I have gotten alot of help from this site.

Kage79

There is no adjusting a power valve. The PV opens when vacuum drops below a pre-set point. To change the opening of the PV you replace it with a PV having a diffent set point.

It sounds like you are thinking of the accelerator pump. Making sure the accelerator pump is adjusted correctly may fix his problem. Or, he may need to try a different pump cam or increase the size of the squirters.

Pump shot length or size...look into it.

I have a 350 mild short block, 461 casting camel hump heads, Comp Thumper (.050" lift=227 Intake and 241 exhaust) Holley Street Avenger 670 (elec Choke), Muncie M20, 3:42 Eaton. I'm getting major hesitation on acceleration right out of the gate on just a normal take-off. I will check the float level tonight. Vacuum is 10" (fyi...power brakes work great). Carb is stock....no mods, 6.5 PV. What else should I attempt to adjust and how? Thanks

Remember this if nothing else.Ignition first..carb second.Post up your initial timing..mechanical advance and any vac advance introduced.The carb is a pretty passive device and simply reponds to what is above and below it.

initial timing is 16....mechanical is limited at 20, Pertronix, Flamethrower, Vacuum advance is connected to "ported Vacuum" on carb. Per Pertronix' tech dept, used one silver and one copper spring inside distributor to achieve Comp Cams "all in" rpm range at 2500 to 2800. Adjusted accel pump and may bump up discharge nozzle to a 35. I might add that the altitude here in Auburn, CA is at 1500'. Smaller jets maybe? Thanks!

initial timing is 16....mechanical is limited at 20, Pertronix, Flamethrower, Vacuum advance is connected to "ported Vacuum" on carb. Per Pertronix' tech dept, used one silver and one copper spring inside distributor to achieve Comp Cams "all in" rpm range at 2500 to 2800. Adjusted accel pump and may bump up discharge nozzle to a 35. I might add that the altitude here in Auburn, CA is at 1500'. Smaller jets maybe? Thanks!

Full manifold vacuum, not ported. What VA can are you running? I run an Echlin VC1810 per John Hinkley's tech paper on timing and advance. Have you read it? My motor's performance was greatly improved using his data.

I have a 350 mild short block, 461 casting camel hump heads, Comp Thumper (.050" lift=227 Intake and 241 exhaust) Holley Street Avenger 670 (elec Choke), Muncie M20, 3:42 Eaton. I'm getting major hesitation on acceleration right out of the gate on just a normal take-off. I will check the float level tonight. Vacuum is 10" (fyi...power brakes work great). Carb is stock....no mods, 6.5 PV. What else should I attempt to adjust and how? Thanks

What size jets are you using? What altitude are you at? I had the same problem and I changed my Jets to stock for my carb, size 66. I then adjusted the idle mixture and curb idle. Problem solved. Dont make the carb more complicated than you need to. Start with basic changes first. Get it setup for stock settings, most likely your carb will work fine then. By the way, what kind of carb is it?

Here... From Holley...

QUESTION My vehicle has a stumble from a dead stop. What can I do to cure this?
ANSWER The most common cause of a stumble is not having an adequate accelerator pump shot. The first thing to do is to look at the discharge nozzle and make sure you are getting a good strong pump shot. If not then you need to inspect the pump diaphram for a hole or tear. You will also need to make sure that the pump passage is clear from any trash or debris. First you will need to check the adjustment on the pump. To do this you will open the throttle all the way (WOT). Push the pump arm lever down and then adjust the pump override spring to obtain .015" clearance between the pump arm and lever. If you are having a stumble and no black smoke out the tailpipe then you will need to increase the shooter size. If it stumbles and you are getting black smoke from the tailpipe then it will be nessasary to decrease the shooter size.

QUESTION I have a vacuum secondary carburetor that bogs when the secondaries come in. What will cause this?
ANSWER Bogging and hesitation are caused by the secondaries coming in too quickly. You can install a heavier secondary spring and this will prevent the secondary from coming in too soon. If the engine is sluggish in response at full throttle then the secondaries may not be opening soon enough. You will then need to go to a lighter spring. The spring kit is part number 20-13 which will have 7 different springs to fine tune with.

Thanks a bunch guys. I value everyone's advice and will check everything and report back. I did notice that the "pump shot" was kinda weak and not like the example on the Holley video. I will re-adjust the accel pump clearance and see if that helps. Cars at the alignment shop and should get it back tomorrow.

I'd like to thank everyone for helping. The car runs great! The problem ended up revolving around that pesky pump cam. It wasn't activating the "pump squirt" as soon as the throttle was cracked open.....there was a delay. Also, Lluciano suggested to get the transition slots in order...they were way off, and, to flip the pump cam. By flipping the blue cam (a $27 kit) it made instant contact with the linkage. Also, my rear floats were too high. I ended up staying with the 31 squirter and 73 primaries. The Holley tech dept gave me some good advice too, but, thought the overall compression of the engine may be too low for the cam and that it could be related to the stumble. Whew....thanks to everyone that responded to my PM's too. It's appreciated!
:beers: