Carter YF 1 Barrel Carburetor Troubleshooting

My accelerator pump diaphragm leaks around the housing

These sometimes become warped and need to be made flat again. Place the housing between 2 flat metal stocks. Heat the housing with some pressure from a vise. Be careful not to melt the metal. 
Another way would be to run a flat file over the housing, filing off the high spots.

Are the carburetor kit parts ethanol ready?

I am looking to purchase a Carter rebuild kit PK105. Are the materials in this kit compatible with ethanol-blended fuels?

Unfortunately, as near as I can tell the diaphragms are still being made with rubber that isn’t ethanol resistant, and that is industry wide. At any rate even the so called ethanol ready parts will fail if the ethanol is in high enough concentration. This means the vehicle cannot sit for more than a week or so. Ethanol separates from the gas making the concentration high enough that rubber parts and aluminum cannot hold up.

One solution is to use Ethanol Defense in your gas. We have had very good feedback on this particular additive.

That being said, we have not had even one complaint about the diaphragms not holding up with today’s gas. Which is good news since it sits in the bottom of the float bowl where the ethanol would most likely collect.

Free Carburetor Manual

Plugs are fouling in 50 miles.

Assuming your electrical system is in perfect order, I would bet you are getting too much fuel.

This could be caused by the following:

Float level off, or perhaps leaking. Heat up some water just prior to boiling, immerse the float, any bubble indicates a leak.
Leaking around the seat. Make sure you installed the gasket under the seat. Check for any cracks, or perhaps the old gasket is still underneath. An problem here would allow the gas to bypass the needle & seat.
Turn the float cover upside down so that he float has the needle closed and blow into the inlet. You shouldn’t be able to blow through (using about 5 lbs).
Run thin wire through all of the small passages. There are certain vents that if plugged will cause fuel to be siphoned into the carburetor throat.
Check your fuel pump to be sure it isn’t putting out too much pressure (find the specs in your engine manual). New fuel pumps are especially suspect. Electric fuel pumps need a regulator installed.
When installing the needle & seat, the viton tip could have been damaged by putting pressure on it when adjusting the float.
Sometimes wiping the needle viton tip with mineral spirits will help. Just wipe until you don’t get any black on the towel.
Test the main discharge to make sure it is sealing when not in use. It could be siphoning gas here if it isn’t sealing.
Jets are probably not the problem unless they are a lot oversized.
If you have the black Nitrophyl type of float, then be sure to replace it. They tend to absorb over time (years). Once they get too heavy, they will start to sink and let too much fuel in.

Gas is coming out of the throttle shaft ends. Too much gas, Flooding.

This means that the carburetor is flooding and when this happens the gas runs down the carburetor and out the 1st place it can, which is the throttle shaft.

Some of the things to look for:
Check your fuel pump pressure and compare with what is in your motors manual. For the YF probably around 4 lbs.
The needle in the needle and seat may be damaged. This can happen when putting pressure on it when adjusting the float. Check the viton tip for any signs of scaring.
Wipe the needle viton tip off with mineral spirits. Wipe until you don’t get any black.
Dirt may have gotten into the needle and seat. Blow out and re-try.
Gas could be coming in the bowl around the seat. Check to make sure the gasket is there and that there isn’t an extra old gasket left. Check for any cracks in the bowl top.
Check the floats for leaks. Heat up some water and dip the float into the water. Any leaks will bubble.
Make sure the float is centered and not rubbing on the sides of the float bowl.
Move the float up & down by hand to see if it catches anywhere.
Check the float level to make sure it is correct.
Spray carburetor cleaner through all of the small passages. One of the air tubes may be plugged causing a rich condition.
Move the float up and down to see if you can feel any resistance. The float pin could be worn causing the float to hang up.
Check the main discharge. Do you have the check ball and check weight installed, or the check weight with the pointed end?
Dirt may have entered the carburetor after it was rebuilt. Make sure you have a good in line filter.

What is Flooding and How Do I Fix It?

The metering rod fits too loose in the main jet.

This is normal for the Carter YF & YFA. The metering rod does not fit tight. It is built to restrict a certain amount of fuel, not to shut if off.

Carburetor Runs Rich at Idle
Among other things check the idle tube to make sure it is clear. Run thin wire down the hole to clear out any ethanol residue. See number 42 in the illustration.

Carter YF Idle Tube

Whilst following your adjustment instructions and when carrying out the metering rod adjustment, Can you tell me if I should disconnect the link pump connector first.

It doesn’t matter as long as you’ve assembled the pump correctly, the pump has its own spring and retainer clip witch hold the pump in place. The metering rod has its own spring and clip witch hold it in its own place, your adjustment is that part only. Hope this makes sense.

Fuel is dribbling out of the main discharge at idle.

This should not be happening. Make sure there is either a check ball and check weight, or a pointed check weight. Seat the check ball using a brass drift punch and tap lightly.
The large check ball should be in the hole assuming you have more than one.

Non vented gas cap can cause this. The tank will build up pressure and force fuel into the carburetor.

Plugged idle tube is another problem.

Does the YF use a fuel inlet fitting?

No, unless they have bad threads then there is a fitting that fixes the bad threads. Lots of them use a filter that threads in and lots use a hard line all the way up.
What is this hole?

This is the accelerator pump diaphragm drain. It returns excess pump discharge to the float bowl. Do not plug it off.

Idle Doesn’t Kick Down When Coming to a Stop

With the exception of a vacuum leak, the idle is affected by the throttle valve being open. What you need to do is figure out what is making the valve stay open.

  • With the engine warmed up is the choke valve open completely? If not, then it is keeping the throttle from closing.
  • The 1st thing to do is remove the carburetor from the engine.
  • Now with the linkage eliminated pump the throttle. Does the throttle valve close completely?
  • Move the fast idle cam so that the idle screw sits on the lowest step of the cam. The throttle valve should be closed. If not, then the fast idle cam might be installed wrong, or is sticking. This will keep the carburetor from getting to slow idle.
  • Turn the idle screw out until it isn’t touching the fast idle cam. Check the throttle valve now. Keep in mind that the idle screw opens the throttle valve, which speeds up the RPM.
  • Disconnect the link that connects the throttle shaft to the accelerator diaphragm arm. Work the throttle to see if the throttle plate closes. If it does then you probably have something wrong with the diaphragm setup.
  • If it all looks good, then take the top off and check the Accelerator pump diaphragm to see if it is put together correctly. See this page to learn about the accelerator pump diaphragm.

After Shutting Down Engine is Hard To Start

There are a myriad of things that can cause this.

Here are a few ideas for you to look at:

  • #1 thing to look at is the ignition. This isn’t our expertise but some ideas are coil, old spark plugs, etc.
  • Percolating – Engine stops and gas boils over – After turning off the hot engine look down the carburetor to see if gas is still flowing into the bore.
  • Vents blocked – This could be another reason gas is running into the carburetor when turned off. Any vents that are blocked will cause a vacuum effect in the float bowl.
  • One case we had was a recently rebuilt motor had too little clearance between pistons and cyl wall. When the engine got hot parts would expand and seize.
  • Test the fuel pump when hot – It might be getting weak. Warning – new fuel pumps often have too much pressure. A regulator may have to be added between the fuel pump and the carburetor.

Only runs when the choke valve is wide open

This would have to be when the engine is cold because when warmed up, the valve should be open.

So assuming it is cold:

This tells me that when the choke valve is closed there is too much gas being pulled into the engine.

  • Check the fast idle. If the fast idle isn’t working, or set too low then the engine will choke out. The fast idle opens the throttle valve so that more air is used.
  • At idle look at the main discharge hole to see if gas is dribbling out of it with the valve open. That would indicate gas is getting siphoned from the main discharge maybe due to the check ball not seating, or check weight above the check ball missing. Also test the check ball to make sure it is seating.
  • Be sure the gas cap is vented. You can usually tell this by driving for awhile, then remove the gas cap. A non vented cap will cause a suction.

Loss of power on the high end

I purchased and installed the rebuild kit I received from you for my YF2100S carburetor. It is mounted on a 1946 Chevy truck with an in-line 6. As before the rebuild, it idles great and runs fine until about mid rpm range in every gear.  Beyond that however the engine starts to spit and sputter.

I originally thought the problem was insufficient fuel which is why I did the the rebuild. Post rebuild, and with no noticeable change in symptoms, I pulled a plug (all new) and found them to be black with soot buildup. So now I’m thinking to much fuel when the throttle is beyond mid-point.

I have disassembled the top of the carb and all appears to be in order. The metering rod seems to be in place. There is no evidence of gas leaking on the outside of the carb. And, as mentioned above it idles fine and runs good to mid range.

A compression test has all 6 cylinders within 10% of each other averaging 115 psi.

The black plugs suggest flooding, or too rich.

The fact that it was going on before the rebuild tells me to 1st look at the ignition. Bad plugs can cause high end loss of power for sure. Same with wires.

Once you know the ignition is OK then start looking into the carburetor.

By chance if this carburetor was transplanted before this all started then the problem may be the carburetor main jet is too big.

Did you test the float when rebuilding? Heat up water just prior to boiling and immerse the float. Any bubbles means it’s leaking.

Gently move the float up and down to see if you can feel any catching. The float pin could be worn. Also the float should be aligned in the middle.

Make sure the  choke valve is wide open when the engine is warmed up.

Check for proper adjustment of the metering rod. If it isn’t coming up far enough it would restrict the fuel.

Look in our YF carburetor manual and go over the metering rod adjustment.

Follow the main jet passageway to make sure it is clear. I’ve seen crud build up below the jet causing a restriction.

Test the fuel pump to make sure it isn’t too low. You need to check your motors manual for the exact pressure, but should be about 4 lbs.


I followed your advice and worked the ignition system. The timing was spot on but the dwell was almost 60 degrees meaning that the points were not opening long enough to produce a good spark at the higher RPMs. Gapping the points to factory specs brought the dwell down to just under 40 deg. Further adjustment is required but the problem is essentially solved.

My YF Lacks Power

Assuming the electrical system is working correctly then you either have a vacuum leak, or not getting enough fuel.

  • Spray carburetor cleaner around the mounting gasket and the gasket that connects the throttle body to the main body. If the RPM smooths out, then you found your leak. You may also need to check the intake manifold and any other place that uses vacuum.
  • Check your fuel pump. It should be about 4 lbs.
  • Check your float level. Use the specification from the instruction sheet.
  • Your needle could be sticking not allowing enough fuel in. You can try wiping off the viton tip with mineral spirits.
  • Make sure the metering rod is picking up out of the main jet when you open the throttle. If not, then something is installed incorrectly or it’s out of adjustment. See how to adjust metering rod.
  • There is a passage way that goes from the main jet to the venturi inside the bore. Make sure that it is clean and clear.
  • The float drop should allow the needle to drop down enough to let fuel in. Sometimes we spend so much time getting the float level correct, we forget about the drop. Remember the drop can be anything as long as it lets the needle drop down, but not so far that the needle gets cocked to one side, or falls out.

Vehicle Doesn’t Run

Adding gas to the bore will get the engine running, but dies.

Obviously the carburetor isn’t getting gas.

Check the float drop. If the float isn’t dropping, then the needle will not be pulled out of the seat and the float bowl will not fill up. Look at the tip of the needle. If any pressure was put on the needle when adjusting the float, then the needle may be damaged not allowing it to open. Test the fuel pump pressure. 4-5 lbs should do it. Did you replace the fuel filter(s).

Vacuum Advance

Carter YF Carburetor Distributor Advance
Carter YF 1 Barrel Carburetor No Distributor Advance.

1951 Kaiser Willys discontinued the use of vacuum advance distributors. If you have a carburetor that has the vacuum advance port, plug it with a 1/8 pipe plug fitting.

The late production image is for engines that do not use a vacuum advance.

Accelerator Pump Diaphragm Washers

Are the washers acting as spacers needed. I see a spacer is optional on some models. Do I need them or should I remove?

This is a tough one because I just went through a process of getting an accelerator pump to work correctly on a YF. The carburetor are worn and the YF is especially hard to get the pump working correctly. The washer(s) can be put above the lower spring and under the top spring. I would try the lower spring 1st.

This will be trial and error by adding and removing washers. Add and subtract then bench test the pump action. You can learn how to do this here:

Hesitation, or Bog

  • With engine off, look down the carburetor. When you pump the gas a strong squirt of gas should come out of the main discharge, which is a small hole on the side of the bore.
  • Weak or no gas then see this page for what to do.

Adjusting Idle Mixture Doesn’t Change Anything

This is indicative of a problem in the carburetor. The list can be long and not in any order:

  • Remove the idle mixture screw and blow through the hole. Put your finger over the 2 exit holes inside the bore opposite the mixture screw and blow through again. This should travel up to the top of the carburetor.
  • Remove the idle tube and make sure it is clear. The passage is small and can plug easily.
  • Check for vacuum leaks. Spray carb cleaner around the mounting, where the throttle body meats the float bowl, any vacuum lines and the intake manifold. Also test your vacuum reading. High vacuum could mean an overly advanced distributor. Check timing.
  • Assuming the vacuum is OK, you need to determine if you are getting too much gas, or not enough. Look at your plugs to see how they are burning. They should be burning tan or light brown. Black is too rich, white is too lean.
  • Check the float level.
  • Look closely at the float and float pin. Manually raise the float to see if you feel any catching. A worn float pin will cause problems.
  • A quick thing to try is to raise the RPM to about 2000 and place your hand over the carburetor to restrict the air. You may have to do the 4 or 5 times. The suction you cause will sometimes unclog a passage.

Page 2 Troubleshooting

Updated on 05/30/2022

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