Mike’s Carburetor


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


Choke Types

We have 4 different types of chokes, Intregal, Divorced, Electric & Electric Conversion.

Intregal Choke

Integral ChokeThe integral choke is mounted on the carburetor, either near the top, or near the bottom. The illustration shows the choke mounted on the top of the carburetor. The thermostat is heated by a heat tube that runs down to the exhaust manifold. The heat tubes heats up the thermostat and moves the choke valve to the open position. A vacuum passage in the carburetor feeds up to the choke housing and helps pull in the heat from the heat tube. Some of these chokes will also have a hot water jacket running through, or on the thermostat to facilitate heating.

Divorced Choke

Divorced ChokeThe divorced choke typs has the thermostat mounted in the intake manifold instead of on the carburetor. In this illustration, the arrow points to the thermostat which is covered by a metal shield. A rod connects the thermostat to the choke lever, which controls the choke valve to be opened, or closed. As the intake manifold heats up, the thermostat mounted, expands, opening the choke valve.


Electric Choke


Electric ChokeThis is a typical electric choke mounted on the carburetor, which is integral. In this case there is one wire on the choke thermostat. This is the 12v source, which all electric chokes use. The thermostat is grounded via the carburetor itself. Some electric chokes will have a 2nd wire (ground wire), which is connected back to the carburetor. When the key is on the thermostat is heated up, opening the choke valve.

Electric Choke Conversion


Electric Choke ConversionThis is a typical electric choke conversion kit. This is used to convert an integral, or a divorced choke to an electric choke. These choke kits come with a temperature sensor that bolts on to the intake manifold, which provides more accurate choke control than with an electric choke without the gauge. The electric choke conversion kit is not used for a manual choke conversion. The choke housing must be in place in order for it to work.
This choke installs in 20 minutes or less with no special
tools. Remove the old choke thermostat and replace with this choke conversion kit.
Attach the temperature sensor under an existing engine bolt.
Wire the positive wire into the vehicles electrical system. Ground the choke to the carburetor.
Complete instructions are provided for each application.


Bobs Carburetor Shop

Recently I was drivingBobs Carbs through Oceanside California and a sign on a building caught my attention. “Bob’s Carb’s”. The 1st thing I thought was WOW, you don’t see many carburetor shops these days. I was curious about the business so I turned off and went inside.

Hi, My name is Mike from Mike’s Carburetor Parts. The gentleman says “Hey I buy parts from Mike’s Carburetor”. Well small world. His name is Mitch and he showed be around and told me a little bit about his family business.

Bob, Mitch’s father started the business around 1955, 1st operating a service station and eventually turning it into a carburetor shop, then a repair shop, which is what it is today. 

Bob’s Carbs has migrated to fuel injection, but they still do a fair amount of carburetor work on classic cars. In fact, they had a Ford falcon in the shop getting the carburetor rebuilt. Mitch’s father, Bob comes in and rebuilds the carburetors and he had a couple on the bench when I was there.

This is not your average shop either. I looked at their reviews and they are very high. Seems they take good care of their customers.


This is Mitch’s view from his desk and he wears shorts year around. What a life.

Carburetor Shop







Like I say, carburetor shops are few and far between and when I discover them, I love to hear the story behind the business. I’ll be in Oceanside again next winter and I will stop in again and say hello.

Carburetor Percolation

Percolation can happen when your engine gets hot, then you turn the engine off and the fuel boils over, sometimes over the top of the carburetor, or more often, simply evaporates. Back in the day we called this vapor lock, which simply meant that the fuel turned to vapor before getting to the engine.

This has been a more common problem these days because our gas has a lower boiling point than it used to. Yup you guessed it, ethanol.

This makes it hard to start the next time. You have to crank and crank, or pour a bit of gas down the carburetor to get the engine started.
What can you do:
  • One of the best ways, but a lot of work, is to run a 3rd line from the fuel pump back to the gas tank. This extra line will help cool the fuel, allowing the fuel pump to pump gas instead of vapor. There are some fuel filters out there that include a return port. There are also return regulators available.
  • Put heat wrap around the fuel line in the engine compartment.
  • Put a spacer under the carburetor mount. These are hard to find so you will probably have to make one. Yup, a mill would be handy about now. And you will probably need to put longer studs in the manifold to accommodate the extra height.
  • Instead of a spacer add extra mounting gaskets. A couple of 1/32 thick gaskets isn’t going to do much. Hopefully thicker gaskets will be available for your engine.
  • Add a helper electric fuel pump. Just before startup, you run the electric pump for a few seconds, then turn it off. Use only a low pressure pump. 7 lbs max. You may end up also adding a regulator because you don’t want the pump to overrun your mechanical pump. Most 1 & 2 bbl carburetor run 4-4.5 lbs. Bigger carburetors might handle 5-6 lbs.
  • Cool the engine with a cooler thermostat, bigger fan, or bigger radiator.
  • Try different brands of gas. Different octanes won’t help you here.
  • Use non ethanol gas if you can find it.
  • Remember when we used to put wooden clothes pins on the fuel line? The clothes pins act like a heat sync, drawing heat away from the fuel line and my wife says the wooden clothes pins are still available at the dollar store.
Anyhow, the basic answer here is to cool your engine and/or fuel.

How a Choke Works Integral Type

When the engine is cold a richer fuel mixture is needed. As it warms up the mixture must be leaned out. This is where the automatic choke circuit comes into play.
Choke ThermostatChoke Thermostatic Coil

The choke shaft extends through the carburetor into a round housing. Inside the housing there is a thermostatic coil spring. This spring will wind & unwind depending on the temperature. When cold the thermostat will hold the choke valve closed. As the temperature warms up, the spring expands and allows the choke valve to open.

Vacuum BreakChoke Vacuum Piston

The choke vacuum piston is linked to the choke butterfly by a small linkage. At idle, which will have full vacuum, the piston will be pulled into the piston well. This puts pressure against the thermostat coil trying to open the choke valve slightly.

Offset Choke Valve

Not all carburetors will have this air valve. Marvel Schebler & the Holley 1 barrel carburetors are a few examples that do. The air valve is placed offset on the choke valve. This keeps the choke from causing a too rich condition.

stove PipeStove Pipe

Most automatic chokes systems will use a stove pipe to heat up the thermostat coil. The pipe heats up, using the exhaust manifold and the heat is then pulled up to the thermostat using vacuum from the carburetor, which is fed by the intake manifold.

Motorcraft 4300 Power Piston

The Motorcraft 4300, 4 barrel carburetor power piston is used to supply extra fuel when powering up.

Motorcraft 4300Motorcraft 4300

The power piston is made of brass (at least the piston itself is) and fits into the float bowl top. See #26 in the diagram. The purpose of the power piston is to supply extra fuel when you are in the power mode. At idle and low speeds, vacuum is at the highest level and pulls the power piston up and off of the power jet (closing it). The power jet is located in the bottom of the float bowl. As you gain power, vacuum starts to drop and the spring on the power piston rod forces the power piston down and pushes the pin on the power jet open. This allows more fuel to feed into the carburetor throat.

It is very important that the power piston works smoothly. When you push on the spring and pin end, the piston should move into the top, then when you let go it should snap back. The power piston is moved by vacuum alone, so it needs to work without any binding whatsoever.

You will need to remove the power valve from the well in order to give it a good cleaning. Buff the brass piston using a wire wheel. Polish the well with crocus cloth to make it smooth. Lubricate with Silicon Spray Lubricant.

Gas Tank Fuel Gauge

For most original gas tanks, the tank gauge unit is located in the gas tank.

Tank Gauge UnitThe tank contains a float that is attached to a resistance device similar to that used in an electric oil pressure sender. See the resistance unit in the illustration. The travel of the float up, or down, causes the resistance to vary, depending on the depth of the fuel in the gas tank.

Most gauges are designed to read empty when one or two gallons of gas is left. This allows the driver to get gas when the gauge indicates empty before running out of gas.

When the float drops, current flow to ground through the bimetal metal coil will be less, because it must travel through the more resistance wire. This cools the bimetal haripin and pulls it together. When the tank if filled the contact slides up, cutting out resistance and current flow increases. This heats the hairpin and the ends separate, causing the needle to move toward the full mark.

Gas Gauge



Tips on Removing Frozen Parts

Over the years I have learned the hard way how to remove screws & bolts that are frozen. Using the techniques below I seldom need any specialty tools for removing screw, bolts & nuts.

Here are some ideas that might help you:

Removing the Small Screws on the Choke, or Throttle Shaft

Take your time removing these screws. It will pay off big time. These screws are usually mushroomed on the threaded end. Using a dremmel tool, grind the threaded end flush with the shaft. Using a screw driver that fits the screw head well, twist the screw counter-clockwise. It is sometimes a good idea to turn the screw back in, then out again. This helps flush out rust particles. Don’t turn too hard, or the screw will break.

Not coming out? Put a block of some kind on the threaded end to prevent the shaft from bending, then hit the screwdriver with a hammer while you try to turn the screw. This will sometimes break the screw loose.

Still not coming out? Using a butane torch heat up the area around the outside of the screw. Don’t apply too much pressure, or you risk bending the shaft.

Did you break the screw? You will have to drill & tap. Using a drill bit (and a good one), just shy of the screw diameter, drill out the screw. If you do this carefully you will be able to remove the screw without damaging the threads. The trick here is to have a good set of small drill bits.

After inserting the new screws, you can mushroom the end, or as I do use thread locker.

Frozen Shafts

The best way to un stick frozen shafts is to heat the area outside of the shaft and tapping on the end of the shaft. The shaft will almost always come loose. If it doesn’t then it is most likely beyond repair.

Frozen Screws, Bolts or Nuts

When a screw is damaged to where a screw driver won’t hold, use a drift punch and hit it a few times with a hammer. This will cause the screw slot to shrink hopefully enough to allow the screwdriver to work. The banging will often times jar the screw.

For bolts use the same drift punch technique to see if the bolt comes loose. Avoid using 12 point sockets. A 6 point will give you a better grip. When a bolt start to loosen, then tightens up, stop. Try moving the bolt back and forth to help loosen it up.

Still frozen? Apply heat around the outside of the screw, bolt, or nut.

Always use good tools and the correct tool on nuts & bolts. That does not include a cresent wrench.

Nut or Bolt Has a Stripped Head

Use a flat file to file the flat parts and remove the mushroom edges. From there try a smaller socket or wrench. Sometimes moving from a US wrench to a metric wrench will do the trick, otherwise a vise grip will be in order. Again applying heat will probably help the nut, or bolt move easier.

Stromberg WW Worn Throttle Shafts

Stromberg Worn Throttle Shafts

Stromberg WW carburetors are notorious  for having worn throttle shafts. Unfortunately unlike most carburetors, the WW wears out the shaft instead of the throttle body.  As I mentioned, most carburetors wear the throttle body and while not a simple process, re-bushing the throttle body on these carburetors is very doable as long as you have the required tools, like reamers and good drill bits. We used to be able to get new throttle shafts to replace the worn shafts, but they haven’t been produced for several years now and finding a used donor carburetor is very difficult unless you happen to find one that has been sitting on the shelf for several years.

To our rescue is someone that I have consulted with many times in the past, “The Old Carburetor Doctor”. Jeff, the owner, has a fix for this problem, which he does when rebuilding the Stromberg WW. He tells me that he will repair your throttle body without a complete rebuild if that is what you want. He just asks that the throttle body be stripped down completely.

Here is what is says about this problem.

Stromberg WWs are no problem. Yes, the shafts are always worn, but we have developed a fix:  I plug the (usually) free right-hand end of the shaft bore with a welch plug, and I rebush the left-hand (throttle lever) end with an extended bushing which allows the un-worn part of the shaft outside of the casting to be supported by new bushing material.  Just look at a WW and you will see how it accommodates this fix; the factory should have done it that way in the first place!

To have your WW rebuilt, you can call Jeff at 800-945-2272. Please do not call Jeff for technical advice. That isn’t what he does. He is a carburetor restoration expert. Leave your technical questions here on this site. Jeff does not sell parts of any kind.

Late to the Electric Party

April 1st, 2016 Tesla unveiled their much anticipated Model 3. Thousands put down deposits, even though Tesla itself says, “Model 3 will begin production in late 2017,… ” That’s a long wait, but early adopters aren’t easily dissuaded, as shown by demand for the impressive Tesla Model S. But just how innovative is the electric car?

1890: the party begins

Electric Car

The first four-wheeled electric Vehicle took to the roads of North America in 1890. Eight years later Ferdinand Porsche (yes, that Porsche,) was driving his electric P1, which he followed with the worlds first hybrid car. By 1900 28% of the cars built in the US were electrically-powered. (Admittedly, only 4,192 cars were built in total that year.)

1900 saw the founding of the Baker Motor Vehicle Company in Cleveland, OH. One of many electric car start-ups, Baker prospered, thanks to a reputation for quality, until the arrival of the electric starter.

What really killed the electric vehicle

The Model T launched in 1908, and the rest is history, as they say. Well not quite. Many people weren’t convinced of the benefits of internal combustion. The early gasoline vehicles were noisy, smelly, and hard to start. They had a crank at the front of the engine that had to be turned by hand. When the engine “caught” and started to run the crank would fly around, injuring more than a few automotive pioneers.

Thanks in large part to Henry Ford’s efforts, gasoline powered vehicles were less expensive than electrics. By 1916 a Model T could be had for $650, (not an insignificant sum,) but an electric roadster would run around $1,730. Economics played a part in pushing out the electric car, and Baker Electric were one of many to cease manufacturing, but the final blow was delivered by one Mister Charles Kettering.

Now largely forgotten, (except by the students attending the college named after him,) in 1912 Kettering invented the electric starter. Instantly, this changed the acceptability of gasoline vehicles. Sales grew rapidly while electrics disappeared, until the late 1990’s.

They’re back!

Electric cars were largely forgotten until the late ’90’s. That was when, responding to a clamor for “greener” vehicles, (mostly from California,) GM created the EV1. An unattractive blob, it was slow with a limited range. Sales were miniscule, but it might be argued this was also the dawn of the modern electric vehicle era.

Toyota launched the first generation Prius in 1997. Initially sold only in Japan, it reached the US in 2000 some months after the Honda Insight hybrid. It wasn’t an instant hit but dramatic rises in the price of gas saw car buyers take notice, and sales climbed.

A hybrid isn’t a pure electric vehicle as it carries a gasoline engine, but the growth of hybrids, along with legislation on gas mileage, stimulated interest in electrics. In 2008 Tesla started selling the electric-only Roadster. In 2010 Nissan gave us the all-electric Leaf, in 2012 Tesla launched the Model S, which was followed by BMW unveiling their i3.

The electric car is most definitely back and you won’t need carburetors, or fuel injectors.

O2 Sensors – Engine Performance from a Capsule

O2 Sensors – Engine Performance from a Capsule

Long gone are the days when car engine were simply using 4, 6 or 8 pistons, a carburetor and a few other auxiliary elements in order to make the vehicle move forward. While, from a mechanic’s point of view, such powertrain units were simpler and easier to fix or upgrade, they featured a big downside: efficiency.

More efficient thermal engines needed a way to create a better mixture of fuel and air and make use of better motion delivering mechanisms, all to generate a bigger power output. While various materials have replaced iron in engine construction to ensure a higher degree of kinematic movement, to enhance air and fuel mixture, you would first need to figure out how much of each product gets mixed within the cylinder.

Obviously you can’t just section a running engine in half to check it out; this is how the need of O2 sensors was created.

Where and how does it work?

In case you are wondering, yes, your car is most likely to have at least one oxygen sensor mounted right at the end of the exhaust manifold. It’s just one of the dozen sensors modern cars use in order to increase efficiency and power output; after all, that’s what all is about: getting more and more of it.

If the term O2 sensor or oxygen sensor doesn’t sound familiar to you, it may be because this very same capsule with a wire at the end is also called a lambda sensor.

Does that ring any bells?

The placement of the O2 sensor on the exhaust manifold isn’t random; in fact, that is the best place to create a precise estimate on how much oxygen actually gets used in the air-gas mixture happening inside the cylinders. There are two main cases:

  1. Too much oxygen

When there’s too much oxygen used while mixing air and fuel, we are calling it a lean mixture. What happens is that during the mix, the air to fuel ratio (AFR) exceeds its preset value. To create a better picture, a regular gasoline engine works at an AFR of about 14.7:1. This means that for every part of gasoline, 14.7 parts of air should be used to attain an efficient combustion. If more oxygen gets through, peak pressure inside the cylinder increases and by default, chances of knock increase. When a cylinder knocks, it can basically create a rotational force that opposes the one generated by the crankshaft, generating severe consequences.



  1. To little oxygen

We’ve found out that too much oxygen is definitely not as good as it may have been initially presumed. However, the other extreme isn’t promising. A low oxygen level within the mixture (an AFR below 14.7:1) won’t allow the entire amount of fuel to be burnt, and thus generate an efficient combustion process. This is called a rich mixture. The immediate result is a considerable increase in fuel consumption; those injectors are pumping more fuel than the available oxygen is able to aid burning.

An oxygen sensor constantly monitors the amount of oxygen output traveling through the exhaust manifold, then sends the acquired data to an Electronic Control Unit (basically a computer for the vehicle) which then adjust the amount of fuel being pushed through injectors into the combustion chamber. Since it’s purely electrical, an oxygen sensor varies its electrical input in order to feed data to the ECU: 0.9V for rich and 0.1V for lean mixtures.

What is it made of?

The probe itself features a ceramic cylinder with platinum electrodes plating both on the inside and on the outside. On top, a metal gauze protects the whole system, like a capsule. It is important to know that oxygen sensors only work effectively while heated at about 600 F (or 316 C). That is the reason why modern sensors also feature heating elements added to the ceramic cylinder, speeding up the heating process. Unlike them, older sensors based solely on the exhaust gas heat to warm up.

Oxygen sensor failures

The best indicative for the wellbeing of an oxygen sensor is the way your vehicle performs. A lower overall performance may be caused by a faulty oxygen sensor, but it isn’t always the case. First of all, it is perfectly normal for a vehicle to exhibit lower performance when cold started. It takes a while for the lambda probe to heat up; until then, since it gets no input from the sensor, the Electronic Control Unit of the vehicle will supply a preset amount of fuel, usually a little above the normal Air to Fuel Ratio.

Electronic Control Units also consider input data from engine coolant sensors when “deciding” how much fuel to inject into combustion chambers; this is why a faulty coolant sensor indicating a higher temperature will cause the ECU to push less fuel through injectors.

If your vehicle traveled more than 100,000 miles, then find out that this equals to the average lifespan of a heated lambda probe. Although you may not feel any serious downshifts in performance, it may actually be a good idea to replace your car’s oxygen sensor with a new one, maybe even opt for a premium product.


Premium Oxygen Sensors

Is there an actual reason you should switch to premium sensors or it’s just a new marketing stunt? The truth is, yes, your car can benefit from having a premium oxygen sensor installed. Considering the fact that premium quality sensors are built with higher grade technology and come with various prerequisites such as coated threads with anti-seize compound, fuel efficiency and power output of your vehicle may shift from good to better.

Although premium sensors are mostly after-market products, they are built by the same brands employed by major automakers to develop OEM parts. It is, however, important to check full compatibility with your vehicle before acquiring a new oxygen sensor.