hesitation when punching it.

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sbh126

sbh126

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I'm running a holley 870 on my 440 and whenever I floor it quickly from idle, the vacuum drops down to 0, engine kinda bogs a bit, then takes off once it hits about 1500 rpms. All this is in the space of about half a second. No bogging or hessitation if I press the gas pedal slightly slower. Any ideas what could be causing this?
 
Rodchester quadrajets were bad about that. Their venturi bleed tubes would drop out of where they are staked unto the casting. Easy fix. Does this apply to your Holley ? I dont have a clue. Good luck
 
65Vsignet said:
The squirter is to small on the carb or accel pump is bad, check your timing too..
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When you say "squirter", are you refering to the jets? or is that something else? Is there a way to test my accel pump to verify if its good or not?

I have my timing set at 15* and all in at 35* at 2500. I tried advancing and retarding it 3* in either direction with the same results.

75Sport said:
How many miles on the valvetrain?
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Brand new, Except for the stock push rods and rockers.
 
sbh126 said:
When you say "squirter", are you refering to the jets? or is that something else? Is there a way to test my accel pump to verify if its good or not?

Yes, there is, with the engine off and while looking down into the carb press on the accelerator and gas should come out of the squirters immediately.

I had the same issue with my 770 Holley Street Avenger. I did the check I described and found that the accelerator was working fine. The next check was of the accelerator lever at the bottom of the accelerator pump. Mine was tight with no play between the lever and the pump, there needs to be at least a .016 inch gap between the lever and the pump, if not you are always in the gas and everytime you floor the accelerator you more or less flood the carb causing the hesitation till your engine catches up. I put .016 inch gap in mine and the problem went away. Hope this helps. All you need is two 3/8 open end wrenches and a feeler gauge. Good luck..
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if the holley is recently rebuilt then no need to worry ..first star with idle screws the need to be 1 and a half turn out only,then bring squirters bigger sizes 35,37,40 and be sure to buy hollow screw for 37 and up ..baseline jetting should be 73 front 82 rear and go from there after u run it...if it still hesitates then u start with the pump camss colors the all do something different...so buy a pump cam kit 2..start small and work ur way up..you put screw in position 1 and then try position 2 and work to a larger 1 and do the same until the hesitation goes away and a good tool is to put a vacumm gauge on ur car in drive at idle and see what the reading is go with the lowest reading is and what i do but everyone is different split it in half anf thats the correct powervalve.. good luck alot of info but its easy if u mess with carbs alot... also u might needto adjust the acc pump arm in between pump cam change..
 
bignasty123 said:
a good tool is to put a vacumm gauge on ur car in drive at idle and see what the reading is go with the lowest reading is and what i do but everyone is different split it in half anf thats the correct powervalve.. ..
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at idle I run about 5" of vacuum. So 2.5 is what I want?
Also what is the difference between dual stage and single stage power valves. What exactly does a power valve do.
 
Is this hesitation a new problem or has it been occuring since a rebuild?
 
75Sport said:
Is this hesitation a new problem or has it been occuring since a rebuild?
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Well I just dropped the motor in and only have a few hundred miles on it. I didn't really notice it until recently. I'm sure its been there all along but I'm just now getting into the fine tuning.
 
I spent the night looking up all the parts in the holley carbs and how and what they do and then tore a spare down that I had in the garage. I have a basic knowledge of how it operates now. I'm going to order a 50cc accelerator pump to replace the 30cc one. I'll order a new powervalve (2.5) and mess with the jetting as well.
How do I know what size squirter to order? Should I just go up 2 sizes and see how it does?
 
Do you have a friend that could loan you a known working carb to try? I have to defer your above question to the Holley guys. I'm a Carter guy.
 
what we do is go closest number i think its a 3.5 go with that....
 
well u need a dounble pumper is the way to go..i have a 4779 750 dp main body..u could go with a 850 base and buy good metering blocks and use the 870 for the rest of the parts i can throw in some parts too if u need them i will see u the main bidy if ur interested and fyi the 750 main with 850 base is thesame thing as a holley 950 hp carb
 
You should not need a 50cc pump the 30cc will work put a 37 squiter in and see how that works, i had the same problem and installed a 37 and it works good.
 
65Vsignet said:
You should not need a 50cc pump the 30cc will work put a 37 squiter in and see how that works, i had the same problem and installed a 37 and it works good.
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It has a #42 squirter in it now. will it hurt to put the 50cc pump on it? I already have it.
 
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