Mike’s Carburetor

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Welcome to Mike’s blog. I hope you find my articles helpful as well as informative. I welcome comments on any of my articles. You might also want to sign up for my email notification so that you are notified any time a new article is added.

We have a ton of technical information for just about any carburetor and new information is being added on a daily basis. Check back again.

For all of your carburetor needs, please visit Mike’s Carburetor Parts.

Thank you for visiting

Mike

Floats

Floats perform an important function in maintaining the correct level of fuel in the float bowl by opening and closing an internal inlet valve. If the float develops a leak, it will sink below its ideal level and excess fuel will enter the bowl. This causes the engine to run rich and probably causes leakage of gasoline out of the carburetor, increasing the risk of engine fires. In a carburetor rebuild be certain to examine the old float for damage or corrosion. You can also test your float for leakage to determine if it needs to be replaced. Repairing old floats is difficult, especially in light of the need to avoid increasing the weight of the float with the addition of solder. Adding weight changes the floatation characteristics of the float.

We have one of the Internet’s widest selections of floats including all floats that remain available and many that are extremely hard to find. We have floats for all of the major name brands of carburetors. These floats are made in the U.S.A. and designed and built to the highest quality standards, including both brass and nitrophyl floats. In some applications, both are available to choose between. We do recommend changing all old nitrophyl floats at the time of a carburetor rebuild, and many mechanics change all floats during rebuilds.

From Holley, Carter, and Motorcraft to Stromberg and Zenith floats, we have them all, including a wide selection of Rochester and Marvel Schebler floats. If it is time for a float replacement in your classic car, scroll our selection and find your carburetor float at a price that will make you smile.

Float Problems and Their Diagnosis:

With brass floats, the floating “pontoon” is typically constructed of at least two brass sections soldered together along a seam. Then a tiny hole used to equalize internal and external temperatures is soldered shut to complete the assembly process. Since all of these points are submerged in gasoline during engine operation, leakage problems can later occur at any place that was soldered. Repairing these floats is quite challenging and replacement is usually preferred unless the float is no longer available.

If your engine is the least bit hard starting after it has warmed up, or if your exhaust has a rich gasoline odor, you probably have carburetor problems, and a bad float is one of the possibilities. Other symptoms include poor gas mileage and, of course, if the engine is flooding.

Is Ethanol Good for my Car?

Classic cars are not the best match for today’s ethanol enhanced gasoline. If you use it in many of the older models, be prepared for earlier component failures. Most automotive parts wear out over time, but ethanol speeds up the deterioration of many, especially those made of rubber or cork.

Older cars with rubber fuel lines are especially vulnerable. A failed rubber fuel line can result in an engine fire. Who needs that? But the fuel line constitutes the most easily addressed area of concern. Other components that are frequently damaged by ethanol include carburetor float valves, rubber accelerator pumps, pump diaphragms and die-cast carburetor bodies, rubber fuel pump diaphragms, galvanized fuel lines and fuel tanks, and gaskets made of either cork or rubber.

Because of its deleterious effects, ethanol rated as E85 (which is only 15 percent gasoline and 85 percent ethanol) should be avoided at all costs. But even the smaller 10 percent ethanol rated E10 will deteriorate components far faster than pure gasoline. Ethanol also attracts moisture, so use a quality fuel stabilizer to help control water retention.

Of course, if you can avoid ethanol altogether, that is your best option. Today there are not many places where you can get ethanol-free gas, but it behooves you to look for them. If you are lucky enough to have a local supplier, seize the opportunity for your car’s sake.

If ethanol cannot be avoided, then make regular fuel system inspections your new standard operating procedure. If your car does not have to retain its stock condition, it is a good idea to install an inline fuel filter so inspection of your gas is easier. Monitor this and the fuel bowl for traces of cork or rubber. If you see either, you already have trouble.

Also inspect the carburetor, both internally and externally. Look for signs of fuel leaks or residue of cork or rubber in the fuel. Check for loosened bolts from weakening gaskets. Check the needle valve. Its replacement may be required much more frequently than in the old days.

Unless the car is driven quite infrequently, regular monthly inspections of your fuel system should be performed and rubber components should be considered for replacement annually.

Of course, if your classic does not have to remain stock, your options increase dramatically. There are now stainless steel fuel tanks available, as well as stainless fuel lines, and they are completely trouble-free in relation to ethanol. There are also replacement carburetors that are impervious to ethanol problems, so if you drive a car that does not have to remain original, these replacements should solve your fuel-related problems for good.

Ethanol and classic cars are not good bedfellows. But a careful regular inspection regimen and timely replacement of key parts can make the relationship at least livable.

Adjusting the Idle Mixture

The Carburetor Idle Circuit and Adjusting the Idle Mixture

The idle circuit is in effect only when idling. Once RPM increases above idle, the Idle mixture screws are no longer in play. If you have the idle RPM set too high, your idle mixture adjustment will be irrelevant. When you turn the idle mixture screw in all the way and the engine doesn’t change, you could have the idle RPM set too high. For example if it was at 1,000 RPM. On the other hand if the idle is normal, then you have a problem in the carburetor, or possibly a vacuum leak.

The idle mixture screws sets the mixture of fuel and air during idle RPM.

Single barrel carburetors will have one idle mixture screw while 2 barrel and 4 barrel usually have 2 idle mixture screws.
You can clean your idle mixture screws by buffing them off with a wire wheel.
Inspect the screw for grooves. Grooves are created when the screw is turned in too tight. Replace any damaged or bent screw.
Inspect the screw hole to make sure it is clear. When you blow through the hole you should get air inside the bore.

For Rochester Quadrajets pick up a idle mixture adjusting tool at most any part store. The tool bends which will make adjusting easier.

When assembling the carburetor turn the idle mixture screws in all the way, gently seat, then turn it out about 1 1/2 turns.

Bring the engine up to operating temperature.
Make sure the choke valve is completely open.
You may have to rev the engine slightly so that the fast idle cam moves to the idle position.
Adjust the idle to specification.

There are a couple of ways to adjust the idle mixture.

1. Using a vacuum meter
Hook the vacuum meter to one of the vacuum ports on the intake, or the carburetor.
Take turns with each idle mixture screw.
Turn each screw out a bit for a start (maybe 1 turn).
Turn each screw in 1/4 of a turn and wait for a second for the vacuum meter to catch up.
Do this until you get the smoothest idle and the vacuum meter stays steady.

2. By ear
Take turns with each idle mixture screw.
Turn the screw out 1 turn to start.
Turn the screw in 1/4 and wait for a second for the engine to catch up.
Keep doing this until the RPM starts to drop.
Turn the screw back 1/4 – 1/2 turn.

Mustang You Gotta Love

Here is an interesting story from one of my customers. We were discussing some of the problems he was having with his Motorcraft 4300 and shared his story with me.

mustang 1

These 4300s did run for some people, at least a mile or two off the lot. When the carb didn’t flood, I really enjoyed the heck out of it. Dad got the ‘Stang from the original owner in ’85 – a nurse who drove it back and forth to work since she started college in ’68. I started working on the car when I was 18 and a novice. Back then you could find interesting random things in the boneyard, even if you had no idea what they were. Every time I saw something different in the junkyard I bolted it on the car. I had no idea what I was doing back then AT ALL so I scrounged around in the busted metal and replaced the Autolite 2100 carb with the aforementioned “Frankenstein” 4300 (unconsciously amalgamated from several T-Bird & Falcon carbs), an intake manifold off a ’66 4-bbl. Mustang, the rear anti-sway bar off a Boss 302, the tall 4-bbl carb spacer off a ’64 Galaxie, the Cyclone headers and fat dump-off exhaust pipes off a Boss 351 as a complete set out of a guy’s garage for $40 back in ’89, and here I am at almost age 50 still with good vision and reflexes with actually still a matching # car if I pull the parts out of the attic except for the original 2-bbl carb which burned up in a 2011 shed fire. And the VIN-matching engine has 164K miles, heads rebuilt by original owner at 70K, and I have flogged it like a rented mule for 30 years come September, with only one C4 rebuild in ’88 and good compression all around.

mustang 2

Back in the ’80s my brothers crashed it 3 times including a diagonal head-on, and then my best friend took out the entire left side backing up out of his garage without looking. The other brother lost control on a “deadman’s” curve and almost launched it at speed off a cliff into a condo subdivision (because he says the tilt-wheel popped up on him – hmm) but just before shooting into space he swerved and folded up the right-front suspension on the retaining curb like an aircraft landing gear. The best friend also lost control & drove through three front yards and a hedge as I tried to teach him to drive, and before I could yank the key he took out an entire sprinkler system that had just been fabbed, still above ground, because he didn’t understand (!) how to use the steering wheel to straighten the car once turning (!). Bumped over a juniper bush & caromed off a light pole dragging new PVC pipes out into the street – my young cousin screaming bloody murder in the back seat – she is now a college professor – and I found a long sprinkler riser and head lodged in the left coil spring when I got home & investigated the noise.I felt very bad because I knew a lot of work had gone into that front yard. That was long ago and we were so very young –  I was dumb to try to teach my friends and brothers to drive in a 289. But they never bent the frame. Used to do 109 on the 1.02-mile strip on the front side of what later became Louis Zamperini Field airport in Torrance, California (same war veteran that Angelina Jolie made “Unbroken” about) before they built all the auto dealerships on Pacific Coast Highway and trafficked up the area. No cell phones back then and anyway no reaction time – they wouldn’t have helped: We’d have one friend wait at the first stop sign halfway down the one-mile strip and flash a flashlight if a car came and another one at the end of the mile to do the same – if no one flashed you’d blow through the mid-way stop at full throttle (109 was the top speed you could make with the 2-bbl before hitting the T-intersection) and the front end would start lifting up on those old Mustangs, the steering getting skittery-light and at the end if no flash then squeal hard and sideways into the intersection at the T as fast as you dared, about 70mph hitting the stop sign jumping on the disc brakes and smoking sideways wrestling the wheel, flat on the Boss sway bar so that you could record your fastest time at the very end of the Airport-Road run.

mustang 3

I still love ramrodding this survivor car when back in California, hammering hard fast and true, in the desert, snow and open road along the coast. I’ve had snow flying crosswise through the missing windows at 10,000 feet but with the Boss 302 sway bar and the right BF Goodrich T/As (P215-70R14 front, P235-70R14 rear) it handles like a champ and I don’t yet want to give up on the carb problem.

There’s my story – :)

Mobile Responsive Web Store

Six months ago our statistics showed that only 1% of our web site users were using mobile devices to view the site. This includes devices like smart phones and ipads. At the time I decided it wasn’t enough to get excited about, but recently we noticed that number had gone up to 20%. That is a huge jump in 6 months and then a customer called me letting me know he was having problems finishing an order on his smart phone. He didn’t use a computer, but could get things done on a smart phone. That is just the opposite of how I thought things would go.

This was an eye opener for me and without hesitation, I got my development staff started on changing the site and we recently launched a new site that is responsive to mobile devices. This means the screen adjusts to whatever device is being used. A smart phone will see it one way and a desk top computer will see it another way. The old version was non responsive and displayed the screen one way, no matter what device was being used and wasn’t all that useable on a phone.

So, let the mobile devices come. We are ready.

Do you use your mobile device to use the internet? I would like to hear from you about how you use it.

Mike’s Carburetor Parts

 

Rochester 2 Jet Fuel Percolation

Throttle Body Venting

I ran across some information about some of the 2 jets that deals with the percolation of gas after shutting off the vehicle. We hear about this problem a lot these days because gas now has a lower boiling point.

Percolation means that the gas is boiling resulting in a very strong fuel mixture. This can make a hard to start situation.

I’m not sure if this was done on every 2 Jet, but it wouldn’t be hard to figure out if you have this feature just by looking at the throttle body (float bowl side).

The purpose of throttle body venting is to give quicker hot engine starting after the engine had been shut down for a short period.

During extreme hot engine operation the fuel in the carburetor tends to boil and vaporize due to engine heat. I said extreme, but gas now has a lower boiling point and it doesn’t take a lot of heat for percolation to happen. Some of the fuel vapor tends to reach the carburetor bores and condense on the throttle valves and seep into the engine manifold. By venting the area just above the throttle valves, hot engine starting time can be reduced to a minimum, on applications where the carburetor is exposed to extreme engine heat.

 throttle vent

There are 2 methods used in venting the throttle bore area.

1. A special throttle body to bowl gasket is used. See figure A. This gasket has cut-out areas which vent fuel vapors from the carburetor bores just above the throttle valves.

2. The other type of venting is accomplished by drilled holes through the throttle body casting just above the throttle valves. See figure B. They serve the same purpose as the vented gasket.

The location of the vent holes are such that they will not disrupt engine idle or off idle operation. They are located above the throttle valves on the side opposite the mixture screws, in an area where the transfer from idle to main metering will not be affected.

Now don’t go out and cut holes to create the vent holes if you don’t now have them. That isn’t going to work. You will most likely create a vacuum leak.

Car Stalls When Putting in Gear

I was recently asked about a Thunderbird that dies when putting the transmission in drive.

This could be caused by a vacuum leak, or possibly it is starving for fuel. Knowing that this particular vehicle has a multitude of vacuum hoses going to the carburetor, I would go with a vacuum leak 1st.

Disconnect all of the vacuum lines from the carburetor and plug off the vacuum ports on the carburetor. If the problem goes away you know it’s a vacuum leak causing the problem. Connect the hoses, one at a time until the problem returns. Obviously if the problem returns when connecting one of the lines, you have found your problem. The hose may have a hole, or something it connects to is leaking.

The carburetor itself could be leaking vacuum. You can spray carburetor cleaner around the mounting plate and the throttle body. If the idle changes, or smooths out, then you found the problem.

If you rebuilt the carburetor check to make sure you installed all of the gaskets correctly. The wrong gasket could leave a passage open to air causing a vacuum leak.

If it is starving for fuel, then you have all sorts of things to look for. 1st, if the carburetor hasn’t been rebuilt, then it may just be dirty, clogging up a passage. The float valve could be sticking, not allowing enough fuel to flow in.

The fuel pump pressure could be too low. Test the fuel pump pressure with a fuel pump pressure tester. On a Thunderbird it is probably around 5-7 lbs, but always check your motors manual for the correct specification.

The float valve could be sticking closed not allowing enough fuel to enter.

The float could be adjusted incorrectly. Check the float level.

I’m sure there are several things I haven’t even thought about. Let me know if you have any suggestions. I would appreciate it.

Visit our technical section for more carburetor help.

Carter AFB Flooding Problem

Gas is leaking out of the main throttle shaft, or gas is coming out of the top vents, or you get black smoke while idling. All of these are indications of too much gas, or flooding.

Here is a list of possible causes in no order of importance.

afb needle & seat
Most float valves (needle) have a black Viton rubber tip on the end. The Viton tip needle may have been damaged when installing. Be sure not to put pressure on the needle when adjusting the float. A damaged Viton tip will allow too much fuel to enter the float bowl. Sometimes wiping off the Viton with mineral spirits to take any residue off will help.
Did you forget the gasket that goes behind the seat. Also make sure the old gasket was completely removed. See #22 in the illustration.
Check for cracks around the seat area. This would allow the fuel to bypass the needle & seat, so the fuel would never get shut off.
The float may be leaking causing it to sink. Heat up some water just prior to boiling and immerse the float. There should be no bubbles.
Gently move the float up and down. You should not feel any resistance or catching. A worn float pin, or improper installation of the float might cause this. If there is a metal clip that attaches the float to the needle, be sure it pulls the needle straight out. Move the clip around until it does. The float could be pulling the needle at an angle and it might cause it not to seal.

Check the venturi gasketmain discharges to make sure they are sitting flat and there there is no old gasket residue left under the new gaskets. See number 32 in the illustration.

Ethanol will leave residue behind and the small orifices of the venturi are subject to clogging. Use thin wire to clean out the small passages. In the past we would have said not to do this because you might make the openings bigger. This is still a possibility, but there isn’t any other way to get the passage cleaned. Carburetor cleaner and air pressure will not remove ethanol residue, so the wire is necessary. Just be careful not to enlarge the openings.

The fuel pump could be putting out too much pressure. New pumps are especially suspect. Test your fuel pump and compare with the specification in your motors manual. It would be somewhere between 4 & 7.

That should cover most problems.

If you had an experience with a flooding carburetor, it would be nice to hear what your solution was.

 

 

 

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

Aside

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