Mike’s Carburetor


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Route 66

Like an elegant actress in her senior years, Route 66 is an institution, a collection of fond memories, and a valued piece of Americana. While the highway number has been decommissioned and alternate route choices are abundant, much of the earlier roadway remains in use. The road spanned eight sates, which may not sound like a lot if you are thinking about states along the East Coast. But it becomes a lot more impressive when that 8-state drive is a whopping 2,450 miles. Today’s I-95 traversing the entire length of the Eastern Seaboard stretches only a bit more than 1,900 miles, running through 15 states and Washington, D.C.

Route 66 is an almost archetypal institution in American history due to its function as the original paved road from the Great Lakes region to the West Coast. Timing was also a major factor in the fame and function of Route 66, as it came into existence in time to meet the challenge of the Great Depression, with many travelers seeking better opportunity “out west.” But this road has an even earlier history, before it became known as Route 66, the “Mother Road,” or “Main Street of America.” Earlier, much of it had been known as the Old Trails Road, and some of it even followed pre-existing Indian trails. But none of its earliest history foreshadowed the greatness that was to become known as Route 66.

U.S. Route 66 was officially established in 1926, but the entire length stretching from Chicago to Los Angeles was not fully paved until the late 1930s. That was just before American novelist John Steinbeck popularized it in The Grapes of Wrath, as “The Mother Road” in 1939. Even the paving of this iconic road was a story in itself. The Depression created a massive unemployed work force, which completed the construction in a major government initiative creating needed jobs.

Popular Culture

After both the novel and the film titled The Grapes of Wrath created the public awareness of Route 66 as The Mother Road, the highway was further popularized by the highly successful pop song, “Get Your Kicks on Route 66″ in 1946, and the iconic “Route 66″ TV series debuting in 1960. The series highlighted seemingly continuous travel on the highway by two young men in a Chevrolet Corvette. The popularity of the TV series may also have been in part responsible for the many re-recordings of the original Nat King Cole song. In any case, the highway has become almost synonymous with leisurely episodic travel in the United States despite the growth of the Interstate Highway system, which was supposed to revolutionize road travel, replacing the need for such “outdated” routes.

The most recent popular surge in the mystique of Route 66 came from the Pixar Animation film, Cars, which details the adventure of several characters in the context of a fictional town, victimized by the construction of the Interstate highway system’s redirection of traffic away from small towns along what is conceived to be Route 66. The movie, Cars, debuted in 2006, and has been followed by two more feature length films, two TV series, and a short film, as well as nine video games, extending the Pixar franchise into 2016 (3rd film’s release). A major factor in the popularity of Cars is its use of references to actual places and structures along Route 66, and featuring the fictional town (Radiator Springs) that imitates both the name and location of a real town (Peach Springs) and implicates many actual settings along the highway.

The Interstate Effect

The film, Cars, accurately depicts the effect that I-40 had on towns along old Route 66, as almost overnight it transformed popular stopping places along a major highway into near ghost towns. Much of the growth that had blossomed along the highway faded into history. Businesses and whole communities died.

It was in 1956 that Congress passed the Federal Aid Highway Act authorizing the construction of the national interstate highway system. While the system as a whole took many years to develop, as each section of Interstate was completed the older routes it replaced suffered immediate consequences. And by 1970, almost all of old Route 66 was bypassed by modern four-lane divided highways. Falling into disuse and disrepair, Route 66 was decommissioned in 1985. But by that time the song, the TV series, and the reality of the nostalgia had already lighted an indestructible fire in the imaginations of Americans. Route 66 simply refuses to be destroyed.

However, not all communities have survived. Even some other industries have reshuffled because of the changes. The auto industry is no exception, with many previous manufacturing plants having relocated. Chicago retains only a shadow of its former contribution to the auto industry, with Ford manufacturing only the Explorer, Taurus, and Lincoln MKS in the Windy City. Today, only General Motors still manufactures vehicles in the St. Louis area. They make the GMC Canyon and Chevrolet Colorado trucks and Chevy Express and GMC Savana vans in the nearby Wentzville plant.

But today organizations and communities have re-energized many parts of the old girl with restoration projects and promotion of her sights, sounds, and memorabilia.

Points of Interest

Hundreds of interesting points remain along this nostalgic path captivating Americans yearning for a connection to the past. Some are thriving businesses, living off of the continuing attraction this highway brings to their door. Others are actual (or practical) ghost towns. One of the more notable communities that now exist primarily as reminders of what used to be, is Texola, Oklahoma. Perhaps one of the most ironically named establishments there, is the Last Stop bar. It is perhaps the only business that remains in operation in the community. Indeed, it is a last stop in several ways.

Never a large community, Texola’s largest census population figure was 581 in 1930. Even during the prime years for Route 66, the town suffered a declining population. Today, there are supposed to be 36 residents, but finding a live person or moving vehicle there is a challenge. Abandoned buildings can be entered at a tourist’s leisure. In 1995, the National Register of Historic Places included in its listings the town’s Magnolia Service Station.

In the movie, Cars, the Cozy Cone Motel is taken from the design of two remaining Wigwam Motels in Holbrook, AZ, and Rialto, CA. Even the name is a reference to another site along Route 66, the Cozy Dog Drive-in in Springfield, IL.

Many museums, gift shops, and memorabilia vendors have grown quite successful along Route 66. One such stop worth noting is the Route 66 Hall of Fame and Museum in Pontiac IL.

At the road’s eastern-most end, a sign post in Chicago beckons the traveler with this message:  “Begin Historic Route: Illinois U.S. 66.” Many maps and books are available to prepare an itinerary for a thorough trip down this historic memory lane. It is well worth the trip, and preparation is a good idea.

A big part of the charm that continues to attract travelers to the quaint and slower-paced scenic route 66 is the fact that it is reminiscent of times gone by, where we lived at a slower pace, with less distraction and more wholesome enjoyment of life. Think of it as a highway connecting you to places a little like Andy Griffith’s Mayberry.

The continuing popular nostalgia of traveling Route 66 is proof that the Interstate has not and apparently cannot kill this proud old matron of travel. If the Interstate is more like actress Kim Kardashian, then Route 66 is our genuine and highly respected Betty White. It is no coincidence that another of the names for this old road is “Will Rogers Highway,” in recognition of another of America’s most cherished figures.

Carter Thermoquad

Throughout the 1970s and early 80s, the Carter Thermoquad (TQ) was a popular carburetor found on many Chrysler products as standard equipment, and on some Ford Motor Company vehicles, as well. The earliest version was in the Competition Series first released in 1969. Production versions followed in 1971 on Chrysler’s 340 c.i. engine. The TQ was discontinued briefly in the mid 70s, then reintroduced as the 9000 series for its final production years.

The Thermoquad was a large four barrel configuraton, with what was called the spreadbore design, two smaller primaries for fuel economy and two large secondaries. When those secondaries kicked in, you knew it. It came standard on many Chrysler engines including the big 440 c.i. mill, most 360s and even on many 318s. International Harvester used the TQ sporadically on its 345 and 392 engines. The big Lincoln 460 c.i. engine occasionally sported the TQ.

A quite distinctive touch on this carburetor was the material of which the main body was constructed. Between the lower throttle flange below and the aluminum bowl cover above, this black phenolic plastic section was designed to provide a cooler operating environment for the gasoline in the float bowl. It worked to effectively lower the operating temperature by about 20 degrees. And this plastic resin main body, then, is what gave the thermoquad its name.

The TQ was a dual bowl carburetor with the bowls housed in the phenolic plastic body. Each bowl served half of the carburetor: one primary and its related secondary. The first thermoquads employed brass floats while the later versions after 1973 were all nitrophyl floats.

The spreadbore design feature was shared in common with other carburetors, even those from other manufacturers, including popular Rochester and Holley designs that shared a common flange connection with the Thermoquad. Therefore many of these carburetors can be swapped out with the right adapter.

The original factory Competition Series of the TQ came in two flow ratings, 850 and 1,000 cfm. Production versions ranged from 750 to 850 cfm. This carburetor was also produced in aftermarket versions rated up to 1000 cfm.

Produced over such a long lifespan, the TQ came in literally dozens of versions, and many parts are not interchangeable from one version to the next. Correct identification of which version your engine carries is therefore critical. There are many different numbers found on the carburetor, but most of them are casting numbers. The actual model number is stamped into the lower left bolt flange at the rear of the carburetor. Some early versions also had a tag displaying the model number attached to one of the mounting bolts. Some later versions also included a bar code sticker identifying the version. Some rebuild kits and all nitrophyl floats remain available.

Buy Thermoquad Carbuetor Kits


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.