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When I purchased my nova it hesitated/nearly stalled when I stomp on the gas. I figured it was probably the accelerator pump so I bought a rebuild kit. I also bought a rebuilt carb so I could rebuild the original carb when I had time and keep the car running. The rebuilt unit I bought runs fine, but I want to get it back to original so I rebuilt the carb using the kit, got it all back together and it still hesitates. I'm sure I rebuilt it correctly. I've rebuilt carbs on motorcycles many times and this one was easy in comparaison.

Anyone have advise on what the problem could be?
 

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What size accelerator pump nozzles are on the two different carbs? The squirters on the original carb may be too small for your setup, but the rebuilt carb may have been modified already to include larger squirters.

They were to small for my setup and it stumbled like crazy off idle.. I think I even need to go one more size up to be perfect, but going from size 28 to size 31 made it MUCH better.
 

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carb

hey guys i just want to ask if a 650 dblp holley would work an a 475 hp motor at the track for now or problems will happen ;
 

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Your assumption is the carb.

Could be timing, vac advance.

Plugs ( always over looked)

Low fuel pressure.

Vacumm leak
 

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This paragraph applies to an instantaneous bog, hesitation, or stumble upon acceleration. Constant hesitation is covered under “surging”. This paragraph also applies to relatively stock engines with the original carburetor. We will discuss two types of bog: the first is bog when the vehicle is accelerated from a stop; the second is bog when the vehicle is accelerated from cruise. Bog from a stop is virtually always (and generally erroneously) diagnosed as a faulty accelerator pump (see the section on “accelerator pumps” for testing). Most modern carburetors are designed to function with roughly 0.020 (20 thousanths) clearance between the center of the throttle plate edge, and the throttle body at a point equidistant from the throttle shaft bearing areas. This clearance allows for maximum velocity of idle air past the idle ports. Exceptions to this are GM carburetors with the idle speed air screw, and end carburetors on tripower. Setting the idle for the highest vacuum idle reading will result in too little clearance of the throttle plate; forcing too much of the idle mixture through the lower idle port and too little through the idle transfer slot. This will cause a phenomena called “puddling” where little droplets of gasoline adhere to the intake manifold runners. When the throttle is opened, there is now sufficient velocity of air to sweep all these droplets into the cylinders, creating a mixture which is too rich to burn, hence the bog. As soon as the overrich mixture is pumped out the tailpipe, and a normal mixture is ingested by the cylinders, the bog disappears. A defective advance mechanism can also cause bog; as can a defective accelerator pump. If bog exists only from an idle, not when accelerating from a constant speed, the idle adjustment is probably the culprit.

Bog from a cruise RPM may be caused by a defective advance mechanism, but on 4 barrel carburetors is often caused by the secondary side opening too soon. Most original equipment 4 barrel carburetors have “on-demand” secondaries (I use this term rather than vacuum, as some early 4 barrels used vacuum to accuate the secondary, while most 4 barrels from about 1960 up used either spring tension or weights to control the secondary). The Carter AFB uses weights, and therefore never goes out of adjustment. Other 4 barrel carburetors such as the Carter AVS, Carter TQ, Rochester 4GC, and Rochester Q-Jet have a tensioned secondary spring. As the spring fatigues, the air valve will open too soon, creating an instantaneous lean condition, and a bog. These units, when rebuilt, should virtually always have the tension spring replaced, and adjusted to factory specifications. A defective accelerator pump will rarely cause bog from cruise.

from: http://www.thecarburetorshop.com/Troubleshooting.htm#Acceleratorpumps
 
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