Holley 2140 & 4000 Troubleshooting

Spring Loaded Needle & Seat

The type of needle & seat which works with the spring-loaded retention system is no longer available. However, the needles used in them are identical to those used with the threaded seat. Some kits contain instructions to simply use the new viton-tipped needle in the original seat and discard the new seat. What Does The Spark Control Valve Do? The spark control valve in the passage from the throttle bore provides an efficient degree of spark advance during periods of acceleration by momentarily providing a partially retarded spark. This partially retarded spark minimizes detonation, or pinging and increases engine responsiveness while accelerating. In effect, the spark valve provides an intermediate spark advance curve between a fully retarded spark and the normal spark advance which would be excessive when the engine is suddenly accelerated. The spark control valve accomplishes this by controlling the manifold vacuum admitted to the distributor vacuum line.

Some of the Holly 4000 carburetors used a needle and seat assembly that has no threads. Our kits have threads on the seat, which replaces the non threaded type. Simply place in the hole ignoring the threads.

A customer reported a problem where the drivers side air fuel mixture screw didn’t change the engine speed. This was after the carburetor was rebuilt. 

Answer: It is probably a vacuum leak due to a bent “boot” at the front of the bowl. You see, one side of that boot has a cast-in breech tube for the idle circuit (which recesses into the idle passage), the other does not — makes no sense whatsoever, but there it is. I’ll bet that it is the side without the breech tube which is causing problems. Put 1 or 2 more gaskets under the boot to see if that will solve the problem without lifting the front of the bowl too high to seal to the choke air horn. Using a very thin coating of Permatex Anaerobic Gasket Maker around the gaskets’ passage holes can’t hurt, either.

Stuck Discharge Nozzles?

Holley 4000 discharge nozzels.

Refer to #30. Please note before doing this that you can distort or crack the bowl housing. Take your time and be very careful. Grind the tip of a screwdriver tip to fit into the keyhole-shaped recess in the top of the discharge nozzle. Try to move the nozzle back and forth, but take your time with this. Any movement at all is a sign that they will probably come out if you work them long enough. Sometimes adding some heat will help. Now using a sharp blade or awl tip driven into them above the “duckbill”, as horizontally as you can, pry against the adjacent casting.


At idle is your vehicle blowing black smoke, or running in a rich state, (maybe you smell the un burned gasoline)? This article may be for you. 

I will bypass any discussion about the electrical system and assume everything, i.e.the timing is perfect. I say this because the carburetor is often blamed 1st when in fact it should be considered last. 

Running in a rich state has two basic possibilities. The carburetor is in a flooding state, or there is a vacuum leak. For the vacuum leak you can spray carburetor cleaner around the mounting flange gasket, intake manifold and around any fitting, or line connected to a vacuum port. If the engine RPM smooths out, then you found your problem. Assuming there is no vacuum leak, then the most likely cause is the carburetor is flooding. In simple terms, flooding means that there is too much fuel getting into the manifold. Here are some things to check out. Eliminate each one carefully.

  • Check the float level. Measure both floats. They need to be the same.
  • Recheck your specifications for the correct setting.
  • Test your float for leaks. Heat a pan of water and when very hot (not boiling), immerse your float in the water and look for bubbles. When heated up, the air inside your float will try to expand and if there are any holes, the air will escape causing bubbles. The smallest of holes will show up this way
  • Did the spring that sits under the float get re installed?
  • Make sure the gasket was installed on the seat.
  • Check the action of the float by moving it up and down and observing the clip that holds the needle to the float. These can get turned the wrong way and cause the needle to bind.
  • Make sure the needle and seat are clear of any dirt. It isn’t unusual for dirt to re-enter the needle & seat after a carburetor rebuild. On the 1st start up after the rebuild, dirt in the fuel line will rush into the carburetor. Spray plenty of silicon spray lubricant through the needle and seat to get it cleaned out.
  • Check the air bleed holes in the top of the float bowl cover to make sure they are not restricted somehow.
  • Make sure the choke plates are opening fully.
  • Make sure the secondary valves are closed at idle.
  • Check for any restrictions in the air cleaner. Plugged air filter for one.
  • A bad power valve will allow extra fuel in the system when not needed. This can be checked by removing the power valve and blowing through it while pushing and pulling the stem in and out.
  • Make sure the power valve diaphragm is working. High vacuum at idle will make the diaphragm stem to pull up away from the power valve. If for any reason the vacuum is restricted to the diaphragm, or the diaphragm itself isn’t working, then the power valve will be open at all times and should be open only at higher rpm.
  • A gas tank vent that is stopped up will cause gas to be forced past the needle & seat.
  • A fuel pump with too much pressure will force too much fuel into the carburetor. This is especially suspect if they pump was recently replaced.

There may be a few more things I haven’t thought about, but this should give you plenty of things to think about. Also, the history of the carburetor should give you some hints on where to start. If this situation started only after you rebuilt the carburetor, then obviously the problem is probably related to something you installed, or forgot to install.

This hole feeds the distributor advance.

Holley 2140 & 4000 Carburetor  Distributor Advance Vacuum

Accelerator Pump

The accelerator pump has a delayer spring that goes over the stem (20), then the retainer (21). The arm #23 slips into the accelerator pump slot above the retainer. The retainer can be replaced by a washer, but you need to figure out a way to keep the pump and spring from sliding around.

The Holley 4000 has 2 idle mixture screws. Only 1 seems to make a difference in RPM when adjusted.

Most likely culprit is warpage in the “boot” on the front of the bowl casting. As the back of it lifts up with the passage of time, the idle circuits and the power valve diaphragm circuit are interrupted. It could also be warpage in the bowl lid since that is where the idle air bleeds are located IIRC. 
Of course, it could also be a blocked idle passage, a vacuum leak on that mixture screw’s primary bore, a missing “boot” gasket or improper bowl installation; hard to say without seeing it.

Secondary Problem

Would you please look at the attached photo and advise if the gasket is the correct one and if it is fitted correctly. I can not see that the vacuum would be sufficient as part of the channel seems to be open to air. I made a new gasket which covered the open part of the channel and the vacuum operates. However when I connect the operating lever to the butterfly shaft it will not operate the secondary flaps. It appears that something is making the secondary flaps difficult to open, even with hand assistance. 

Holley 4000 4 barrel carburetor secondary

The gasket is correct; it has simply been installed incorrectly. Tell him to line up the holes in the gasket with the four holes in the base casting, then install the secondary vacuum main body. Only after the main body has been installed should the diaphragm be loaded into it and clipped to the little secondary lever. 
The slot in the bottom of that secondary casting is there for a reason: with the steel cover plate in place, it allows a small instrument to be inserted to prevent the sec. lever from moving while the spring & diaphragm cover are installed, thereby pre-loading the diaphragm correctly. Tell him to be sure that the large check ball and its keeper are in the sec. casting’s vacuum channel as well; this is very important. 
Not sure I understand his comment regarding the secondary “operation lever”. The purpose of that linkage between the primary and secondary levers is to close to the secondary’s, not to open them; the diaphragm spring takes care of the closing chore entirely. The linkage should be adjusted so that it just closes the secondary’s completely when the primaries close completely (fast idle cam disengaged, curb idle screw backed completely out). 

Red Nylon Check Ball

The small red plastic checkball goes under the small brass screw located in a hole on the bottom of the base. This is part of the spark vacuum control system. Also, make sure that the vacuum advance restriction jet (a tiny brass jet) is installed beneath the spark control valve.

Float Bowl Empties Gas

The problem is that if the car is started each day, it will start immediately, almost on the first crank. The car runs, idles and performs very well. However, if the car sits for three-four days, it must crank for some 30 seconds or more before it will start. We have removed the top of carb and found that after three/four days the fuel bowl fuel level is way down. 
Actually, Mike, this is easy: it’s not the carb, it’s the fuel pump. Failing fuel pumps which are draining back into the tank through faulty valves or back through a faulty diaphragm into the crankcase (cringe!) will empty a carburetor bowl in as little as a day or less. Tell the customer to disconnect the fuel pump, then wait 3-4 days and check the fuel level in the bowl — betcha it will be full. Then tell him to send his pump to The Old Carb Doctor for restoration. It will cost $210 + shipping to restore his dual-action fuel pump.

The old spark valve is longer than the new one.

Holley 4000, 4 Barrel Carburetor Spark Valve
The one on the right is a newer design and works the same.

I am rebuilding a Holley 4000 Carb from a 1956 Ford Thunderbird. I have two issues. I can not remove the Pump Discharge Weight and the two Main Discharge Jets from the float bowl body after dipping in Berryman’s carb cleaning dip and spraying with a spray carb cleaner. Any recommendations for for freeing them up or is it OK to leave them and continue with the rebuild? The second problem is that the small arm that sticks out to the side of the main discharge jets came off as I tried to pull them out. Will the carb function without them?

You can apply heat around the outside of the parts. That usually gets them loose. If you can’t get them out, be sure you can blow air through them then leave it alone.They should be cleaned. If you are referring to the main discharge nozzles, then yes they need to be there. The small arm that sticks out the side is where the fuel comes out. If it is long enough to get the fuel into the bore, then it will probably be OK. These are very hard to remove without breaking. If you can’t get then out, be sure you can blow air through them then leave it alone. Unfortunately the main discharge tubes are not available and there are a lot of variations depending on which carburetor you have.

Are the ‘pump rod lubricator washer and seal’ available?

The felt lubricator is available here, Felt Pump Rod Lubricator

From a rebuilder: There is, or was, a tiny thin steel washer above the felt seal. Problem: most of those washers are now missing and I don’t know where you would get one to replace it. Moreover, I’m not sure why it needs the seal and washer in the first place. I don’t try to replace them; instead, I lube up the polished pump shaft with some Lubriplate No. 105 assembly grease from NAPA and send ’em out seal-less. I would suggest that your customer do the same. Even if he finds a new washer there is a very great likelihood that the shaft will get into a bind with the felt upon assembly.

Have to Prime Gas to Get it Started

The most likely cause is the accelerator pump. Look down the carburetor and pump the gas (engine off). You should see 2 good gas squirts.

Is the choke closed (when cold)? If not then adjust, or replace the thermostat. The carburetor could be boiling over (percolating). This happens when the engine gets hot and you turn it off. The gas having a lower boiling point these days, will boil and evaporate, causing the float bowl to dry. Make sure the gas lines are away from the manifold, try other brands of gas, run a 2nd fuel line back to the carburetor to help cool the gas.
Some have gone as far as added an electric fuel pump which they use only before starting to fill up the float bowl.
Test the fuel pump. Check your auto manual for the correct pressure. If the vehicle runs OK after starting, then this is most likely not the problem.

Fuel Dribbling Out the Accelerator Pump Nozzles.

Watch the nozzles at idle and also at a constant higher RPM. Remember that any pumping of the gas will push gas through the nozzles. Any leaking, or dribbling is a problem.
Make sure the pump discharge needle is in place and holding. To test, fill the bowl with fluid (mineral spirits) and while holding the needle down gently pump the accelerator. Fuel should not leak around the needle. If it does, inspect the needle for damage. Seat the needle by hitting it gently with a brass drift punch.
Make sure all vent holes are open. The gas cap should be vented.

Fuel Leaking Around the Fuel Inlet

The plug will have a gasket. Apply Permatex Anarobic to each side of the gasket. This type of sealer is used on surfaces that are clamped together. Use is sparingly. You don’t want residue getting into the carburetor.

Only Runs With Choke On

This is caused by one of 2 problems. Vacuum leak, or not enough gas getting through. Here is a list of possible problems not in any order.

  • Vacuum leak – spray carb cleaner around the carburetor mount, intake manifold and any vacuum line. If the RPM picks up or smooths out you found the problem.
  • Clogged fuel filter.
  • Bent or clogged fuel line.
  • Passage plugged – With carburetor apart squirt carburetor cleaner, or compressed air through each passage to be sure it is open.
  • If the engine sat for months then the gas may have turned and coated the carburetor, gas lines and gas tank with varnish. This is hard to remove. Most carburetor soaking products will remove the varnish. Depending on how you cleaned the carburetor, the varnish could be plugging things up.
  • Float out of adjustment.
  • Float hanging – manually lift the float up and down and feel for any binding. Also be sure the float isn’t rubbing anywhere. They do fit tight in the bowl.
  • Look for any obstructions in the needle & seat. I found a bug wedged in the inlet on one carburetor. Must have crawled in when the carburetor was open.
  • Weak fuel pump – test the fuel pump pressure. Compare the pressure with your motors manual. Look for 4 lbs prox.
  • Make sure the air cleaner is secure and tight.
Updated on 05/28/2021

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