The B&B or Ball & Ball Accelerator Circuit Gone Bad

checkballdischarge b&bpump check inlet





Here is the question. When I accelerate the engine bogs down, or dies.
Assuming the electrical system is OK, because the distributor advance will act the same way, so check that out also.
The first thing to do is turn the engine off and look down the bore of the carburetor. Pump the throttle and you should see a squirt of gas come out of the main discharge. This is located just under where the carburetor top mounts (see #28).
No squirt, or weak squirt indicates a blockage in the accelerator pump circuit. Remove the aluminum plug where the main discharge is located. See #27 in the illustration. This plug is included with our Carter B&B carburetor kits. Remove and clean the main discharge jet #28. Be careful removing this jet. They get stuck and will break easily and if it doesn’t come out easily, then leave it in and clean it out the best you can. Run thin wire through the jet to make sure it is clear.
Your carburetor may have an intake check ball located at the bottom of the accelerator pump well with a retainer wire holding it in the hole. If you don’t have the hole, then a check ball is not necessary here. The action of this part is as follows: When the pump returns to the top, gravity pushes fuel up through the bottom hole and lifts the check ball up, allowing the pump well to fill up with fuel. You can add some fluid into the float bowl and watch to see if this does happen. If your carburetor kit includes an aluminum check ball, then this is where it resides. If you can’t get fluid through this hole, then it is plugged up. Try blowing air through it. When accelerating this check ball will close keeping fuel from going back to the float bowl. Seat this check ball (only if not aluminum) by tapping on it with a brass drift punch.
In the bottom of the float bowl close to the accelerator pump well will be another check ball inside a small column. The column will have either a cap screw, or an aluminum plug covering the check ball (#29 & #30). This is the discharge check ball. When pressing down the pump, fuel will force this check ball off the seat allowing fuel to reach the main discharge.
Test the 2 check balls this way. Hold down the discharge check ball with a brass drift punch. With the pump well full of fluid press down on the pump. You should feel some resistance. If you suspect this ball to leak under this test, tap on the check ball with a brass drift punch to seat it. Now press down on the pump (full of fluid) and see if the fuel lifts up the discharge check ball.

How To Measure A Part


Measurement Toolsby John Klyzek

How do you tell someone what size something is?

What diameter is that hole?

How long is that part?

What we are really doing is comparing the size of the item in question to some known or agreed upon standard.

What is the standard? Is there more than one kind?

In the old days a foot was the length of the Kings foot or a meter was a fraction of the distance from the north pole to the equator..

In the United States we use two basic systems commonly referred to as the English system or the Metric System.

The English system commonly uses the inch and foot  for measures of length.

The Metric system uses the meter and millimeter.

How long is a millimeter?  1/1000 of a meter. Mil refers to one thousandths of something.

For more precise measurements we divide a known standard length into smaller divisions.

Ever hear a mechanic or a machinist say “it’s bored 30 thou over” or “ bored 30 over”.

What does that mean?

Bored refers to a machining process called “boring”, but let’s concentrate on the “30 thou” part for now.

Thou is short for thousandths of something.

30 is short for the decimal equivalent of 30/1000 or .030

Most precision measurements in the USA are expressed in thousandths of an inch.

So when the guy says 30 thou in the USA he usually means .030 of an inch.

How big is that? Roughly 10 times the thickness of your hair.

One thou is 1/1000 or .001, 2 thou is 2/1000 or .002  and 500 thou is 500/1000 or .500 of something, could be an inch, meter or a potato.

Pick a unit of measure and tell me how many of those units it is.

Some of the time it is some number of units plus some fraction of a unit.

You could say the part is 2.500 inches or 2  1/2  inches long.

You could also express that same measurement in the Metric system.

How many millimeters is 2.5 inches?

Since there is 25.4 millimeters in an inch, the answer is 2.5 multiplied by 25.4, or 63.5  millimeters.

In the USA we are stuck using both systems for now.

When you express a dimension use the unit of measure that fits the situation.

If you talking to a farmer in Oklahoma about a cotton picker he is probably talking inches.

If you are talking to Europe or Asia they are probably talking Metric.

For clarity you can always say 2.500 inches or 2.50 mm or millimeters to be sure the recipient knows what unit of measure you mean.

Get your micrometer and calipers out and practice measuring something that has a known dimension, like a drill bit.

See if your measurement is accurate.

The accompanying chart is a shortcut method of comparing the same length, expressed 3 different ways.

This chart has fractions of an inch, decimal expressions of an inch and decimal expressions of a millimeter.

Let’s talk about 1/2  inch. Find that in the fractions and notice it’s also expressed as .500 of an inch in decimals and 12.7 mm in Metric.

All 3 of those are the same length just described different ways.

You need to drill a hole the size of a  linkage that goes in that hole.

I measure the linkage and find that it is .187 inch in diameter.

I only have a fractional drill bit set. What size drill will produce a .187 diameter hole?  3/16 of an inch is the correct answer.

This chart saves me time figuring out the correct drill.

There are dozens of kinds of charts like this and we will have them available on our website.


Fraction Decimal Millimeter Fraction Decimal Millimeter Fraction Decimal Millimeter
1 1.0000 25.4000 21/32 0.6562 16.6687 5/16 0.3125 7.9375
63/64 0.984 25.0031 41/64 0.6406 16.2719 19/64 0.2969 7.5406
31/32 0.9688 24.6062 5/8 0.6250 15.8750 9/32 0.2812 7.1437
61/64 0.9531 24.2094 39/64 0.6094 15.4781 17/64 0.2656 6.7469
15/16 0.9375 23.8125 19/32 0.5938 15.0813 1/4 0.2500 6.3500
59/64 0.9219 23.4156 37/64 0.5781 14.6844 15/64 0.2344 5.9531
29/32 0.9062 23.0187 9/16 0.5625 14.2875 7/32 0.2188 5.5563
57/64 0.8906 22.6219 35/64 0.5469 13.8906 13/64 0.2031 5.1594
7/8 0.8750 22.2250 17/32 0.5312 13.4937 3/16 0.1875 4.7625
55/64 0.8594 21.8281 33/64 0.5156 13.0969 11/64 0.1719 4.3656
27/32 0.8438 21.4312 1/2 0.5000 12.7000 5/32 0.1562 3.9688
53/64 0.8281 21.0344 31/64 0.4844 12.3031 9/64 0.1406 3.5719
13/16 0.8125 20.6375 15/32 0.4688 11.9062 1/8 0.1250 3.1750
51/64 0.7969 20.2406 29/64 0.4531 11.5094 7/64 0.1094 2.7781
25/32 0.7812 19.8438 7/16 0.4375 11.1125 3/32 0.0938 2.3812
49/64 0.7656 19.4469 27/64 0.4220 10.7188 5/64 0.0781 1.9844
3/4 0.7500 19.0500 13/32 0.4062 10.3187 1/16 0.0625 1.5875
47/64 0.7344 18.6531 25/64 0.3906 9.9219 3/64 0.0469 1.1906
23/32 0.7188 18.2563 3/8 0.3750 9.5250 1/32 0.0312 0.7937
45/64 0.7031 17.8594 23/64 0.3594 9.1281 1/64 0.0156 0.3969
11/16 0.6875 17.4625 11/32 0.3438 8.7312
43/64 0.6719 17.0656 21/64 0.3281 8.3344