Hesitation problem!!!!

[undertaker81]

Good evening ghouls and goblins. I need some serious help. I have a 78 s&s victoria. 425 ci, and quadrajet. I recently had my carb rebuilt and a tuneup done. But now my car hesitates. She starts and idles fine. But under acceleration and going up a hill she almost cuts off unless I take my foot off the throttle. I have replace the fuel filter and pump and still no help. Timing was checked and that is fine. Can someone please help me...

[northgahearse]

Sounds like the accelerator pump inside the carb,

[undertaker81]

The kit that was used to rebuild the carb had a new accelerator pump in it. could it still be bad? the kit was from napa.

[northgahearse]

it can happen that rubber gasket around the acc pump
if it does not seat just right as the carb top is put on and what a fun task of getting the metering rods and the spring loaded acc pump to play along
the rubber gasket can rip get all sideways or just be a bitch.
being the carb was just rebuilt thats my first guess
did you do the rebuild yourself? the first time almost never plays out well lol

stole this from a sight the well plugs are another thing to deal with when you have on apart

The Rochester carb is the most common carb found in GM cars and trucks from the 1960's to the mid-1980's when they were replaced by fuel injection units. If the carb is maintained properly, it will deliver years of service. There are a few problems with the Rochester carbs as they get older and/or are not maintained.

A common problem is the fuel filter inside the fuel inlet housing becomes plugged with debris from dirty gasoline. This prevents the float bowl from filling quickly and results in poor engine performance. This filter is not an ideal candidate since it is made of paper and can not be seen unless the filter is removed from the housing. The best filter to use is a glass filter connected in-line between the fuel pump and carb. This filter allows you to see if the fuel pump is working as well as if there is any debris in the fuel.

Another problem is the cam that raises the secondary metering rods when the air valves open. This small heart shaped plastic cam is located between the secondary air valves on the air valve shaft. It is common for this part to break preventing proper operation of the secondary air valves leading to a bog.

Another problem associated with the secondary air valves is the vacuum secondary break. This small vacuum break is located on the passenger side of the carb. These small diaphragms rupture after years of exposure to heat and result in the secondary air valves flopping open causing a bog.

A couple of other problems but not common are the carb being bolted to the intake with excessive torque and fuel well plugs leaking. If the carb is overtightened with the four bolts mounting it to the intake the air horn will be bent creating fuel leaks and vacuum leaks. Always change the base gasket when installing a rebuilt carb for it to create an air-tight seal between the carb and intake. The fuel well plugs can leak and the best way to fix them is to use an epoxy to seal both wells. The wells are located under the bottom of the fuel metering rods.

[undertaker81]

It was professionally rebuilt. Do you now of a way to check the daiphram for the secondaries? And will adjust how fast the secondaries open help? I saw a video on line about adjusting the secondaries to help prevent quadrabog. Have you ever tried this? Apparently all you need is a 3/32 allen key and a flat head screwdriver.

[Dickey]

Your title says the trouble is a hesitation but in your post you indicate that the car wants to cut off when accelerating or going up a hill. A hesitation is a momentary stumble and then the car picks up as expected. An engine nearly cutting off until you let off of the gas pedal is a different matter entirely. Which are you experiencing?

That said, if the secondaries were completely disabled on an otherwise properly running car, it would still run and drive without any issue aside from not developing as much power as having the secondaries opened would allow.

[undertaker81]

I am experiencing the latter. Forgive me I wasn't sure how to title it. My car is almost cutting off until I release the gas!

[Dickey]

If your timing checks out, you are almost certainly experiencing a fuel delivery issue. This could be carburetor related or it could be well before the carburetor. What prompted you to get your carburetor rebuilt? How was the car running at that time?

I ask because I've run across similar situations that turned out to be failed pressure regulators, a clogged pickup sock in the gas tank, the tiny filter thing at the fuel inlet for the carb and once I had a fuel pump that seemed to test adequately but wasn't moving enough volume to suit the engine over 2300 rpm or so.

[undertaker81]

Before the carb was rebuilt, I would hit the accelerator and it was like the car had to think for a second before it took off. My timing has been checked. So You might be right about the regulator. I didn't know a car this old had those. Do yo have any idea where it would be located?

[Dickey]

I always convert to electric pumps with pressure regulators. Old habits for me is all.

If your car is factory it just has a mechanical pump located on the engine. They require no regulator as their output varies with the engine rpm. Were I in your position, I'd consider picking up a $40 fuel pump and a $20 pressure regulator to remove it from the equation and keep on the shelf as a debugging tool if your pump proves not to be an issue. You could also T in a fuel pressure gauge (1-8 psi will be sufficient) to see what kind of flow you're getting just before the carb.

[undertaker81]

Thanks for the help. I will give it a try.