Motorcraft jet size chart

Welcome to the ClassicBroncos. To take advantage of all the forum features please take a moment to register. Registration is fast, simple and absolutely free so please, join our community today!

If you have any problems with the registration process or your account login, please contact contact the admin. If you've lost your password click here. Motorcraft Jet Sizes.

I am about to start the rebuild on a Motorcraft and in the process of unscrewing the jets that were nearly permanently stuck in place I chewed up the thread pretty bad. I can see on the one jet that the number reads 50 but on the second jet the first number is unclear.

Autolite & Motorcraft Carburetor Main Jet Assortment

If I had to guess based on what I can see it looks like it may say 60, but I'm not positive. It's a if that helps ruling things out. Any help is appreciated. Thanks for your time. They both look like A stock carb would have What size ventiris does it have? All the EB s came with either or s that had 1.

Carb Adjustment Basics - Jet Logic/Perfecting the Tune

With 60 jets you may have a larger carb, say 1. Some PO may have put 60s in a stock carb, mistakenly thinking it would yield more power. The venturi size is cast on the drivers side of the float bowl. Thanks for the reply. I checked out the numbers you said to look for and it seems I have a 1.

Thanks for your time! Be Well, Our77Bronco.Ok, probably not. In fact, jetting your dirt bike is probably one of the most, if not the most dreaded part of maintenance. Unfortunately, it's not something to deal with later and keep putting off.

In simple terms jetting your dirt bike's carburetor is determining the proper air-to-fuel ratio the engine receives. Running the correct ratio of fuel and air makes your dirt bike run optimally. Most dirt bikes off the factory floor might look pristine but probably need jetting.

A number of factors influence whether or not you'll need to jet the carb including the following:. Four strokes tend to be more forgiving then 2-strokes when considering the factors above however riding at sea level where bikes run leaner and then in the mountains richer messes with any bike's jetting.

After breaking in your dirt bike it's easy to determine whether you need to jet the carb simply by looking at the spark plugs. Take the plugs out and if they look clean you're good to go.

However, if you see black soot then you're running rich - meaning you've got too much fuel - if you see white residue then you've got too much air flowing in or you're running lean.

You can also determine if you need to jet the carb based on how the bike rides. However, if your bike can take off in a sprint but lacks overall power, then you've got too much air. As you can see the carburetor consists of several parts that work, sometimes in unison, to influence the mixture of fuel and air. This is where it gets easy but tricky at the same time. If you're running rich, for example, you'll need to check the main jet, jet needle and needle jet.

However, you only need to tinker with the main jet and if that solves the problem you found the easy solution. If it doesn't solve the problem then you'll need to check the jet needle and then the needle jet. Don't mess with all three jets at once.

Change the main jet first and see if that solves the problem. If it doesn't, you'll need to reestablish the main jet to its original position and then move on to the jet needle and so on. Follow the same procedure if your bike runs lean. Your bike might run rich in the late summer months and then run lean come early spring. Similarly, a trip to the beach might require some adjustment if you last rode in the arid desert.

Elevations also mess with jetting because of the dense air. Higher altitude thinner air requires less fuel or leaner jetting to run correctly. Many dirt bike owners go the OEM route for new jet kits however aftermarket jet kits often work just as well if not better.The jets on a carburetor meter the amount of fuel that enters the throttle bores of the carburetor where it mixes with incoming air.

If the engine shows performance problems such as stalling or sluggish acceleration, you'll need to change the jet sizing. Jets are threaded and have a small orifice through their center that varies based on the size of the jet.

For example, a jet may be stamped on its head with the number This indicates that the jet's size is 30 mm. Installing a smaller size jet will reduce fuel flow, which is ideal for high-altitude conditions where air is limited, where a larger jet size increases fuel flow for oxygen-rich, low altitudes. With this knowledge, you'll be able to understand how to correctly change the jets to regain the engine performance levels that were lost due to improper jetting. When the operating altitude of the engine will be feet higher than your normal altitude, you'll need to insert a jet one or two sizes smaller than the size currently installed in the carb, which reduces the amount of fuel entering the engine to match the reduced level of oxygen in the air.

If the altitude is dropped feet, you'll need to insert a jet that is one to two sizes larger than the current size, increasing the fuel flow to match the higher oxygen levels. An incorrect ratio will show in decreased engine performance. Unscrew the fuel bowl bolts with a wrench and pull the fuel bowl off the carburetor. Save the gasket that was pressed between fuel bowl and the carburetor's metering block what the fuel bowl is bolted to.

With the bowl off, the jet s are exposed and can be identified by their brass color and center orifice. Unscrew the jet s with a screwdriver or pair of pliers and note the size stamped on the jet's head. As mentioned in step 1, you'll need to increase the jet size for lower altitudes, while a smaller jet size will be needed for higher altitudes. Make the size change in increments of one to two sizes at a time.

Screw the new jet size into the jet mounts within the metering block, with a screwdriver or pair of pliers.

motorcraft jet size chart

Press the fuel bowl gasket and fuel bowl against the metering block and tighten the bowl bolts with a wrench. Turn the engine on and test it by listening for a smooth idle and a crisp throttle response. If the carb continues to under perform, remove the bowl and make another one to two jet sizing adjustment, either up or down based on your circumstances, until the engine runs well. Install a smaller jet size if the ambient temperature dips below degrees Fahrenheit. This creates a lean condition that runs the engine hotter, ideal for cold conditions.

If the air temp raises above degrees, larger jets will be needed to increase the amount of fuel entering the combustion chamber, known as a "rich" condition.

Rich conditions allow the engine to operate at a cooler temp. Unbolt the fuel bowl bolts from the metering block of the carburetor. Pull the bowl away from the carburetor, preserving the bowl gasket. The jet s are now exposed and can be identified by their center orifice, screwed into the metering block.One of the things we noticed over the years is the lack of information concerning Holley List numbers and the specifications for individual carburetors and their stock jetting.

Many folks buy a used carburetor at a swap meet or from an ad and find out that it wasn't what they thought they were buying. An cfm "double pumper" turns out to be a cfm with vacuum secondaries.

motorcraft jet size chart

In an effort to help our viewers identify which Holley carb they have or what carburetor they want to buy, we've put this list together. Holley itself has a huge website at Holley.

Holley 4 Barrel Carburater Information

Holley also has a catalog of all of their "Performance Products" and services, updated yearly. If you need one, contact them for a copy. Among many other things, the catalog lists every performance and race carburetor they make and the indivdual specifications for each carb. Such a list would be too big on our website, so we are going to list the most popular Holley four barrel carb List 's and their cfm size and stock jetting specifications.

When you buy a used carburetor always check the jetting.

motorcraft jet size chart

Over time folks are always changing the various parts in a carb and it can be far from the original baseline stock setup. Once you know the baseline setup you can make appropriate changes to improve the carb's performance. Most square flange Holley carbs have the "List " stamped on the front, driver's side of the choke horn. Dominator carbs have no choke horn and their list is stamped on a flat portion of the venturi area on top of the throttle body.

The newer "HP" line of four barrel carbs have the "List " on the driver's side of the throttle body. Keep in mind that the stock jetting listed is for applications at sea level and at 70 degrees carb inlet air temperature and is meant to give you the baseline calibration.

If you live at a higher altitude or in warmer or colder climates, changes can then be made appropriately.

Likewise, the power valve calibrations are stock baselines. If you have a longer duration performance or race cam you may need to change the power valves to handle reduced engine vacuum signal to the carb. These carb tuning aspects are discussed on our Holley Tuning Tips page. The following is a partial list of Holley list numbers for some of their most popular carburetors. It is not a complete list. Holley 4 Barrel Carburater Information List Numbers and Stock Jetting One of the things we noticed over the years is the lack of information concerning Holley List numbers and the specifications for individual carburetors and their stock jetting.

Ask in our Car Mechanic Forums!Carburetor Size Calculator This is a simple calculator for determining the approximate size of a carburetor. The Volumetric Efficiency is a bit more tricky and is at best a guess unless you have had your engine on the dyno.

Note: These are for normally aspirated engines where the carb does not sit on a blower or otherwise is used on a draw through blown application. These numbers are typically for 4 barrel carburetors. The last bit of confusion is the carburetor type.

This selection give a bit more modern approach to the size. The thinking behind the increase in CFM is that a well prepared race carburetor has a much better fuel atomization and can perform better at lower vacuum ratings then a stock carb so you can use a larger CFM rating. Race carb info from www.

As always call an expert at a tuning shop like the above they will give you more information they you will care to know about. The graphs will help you get a visual range on what size you will need. Open plenum carbs sizes can generally be smaller then a 2 plane manifold. These numbers do not apply to IR type manifolds typical of Weber carbs. Your on your own with them, and good luck and use as a general gauge for sizing your carburetor.

Remember, Right Carb, Right Cam, Right Intake and Right Exhaust for your application will be the optimal solution as it's a package that must all work together. Scroll down to view the graphical results! You can zoom the charts by using your scroll wheel on the mouse or selecting an area of interest on the chart with the mouse. Click areas of interest in the charts to see data points of interest. Double click in the chart area to reset its view to see all data.

All Rights Reserved. Content May NOT be used without written permission. Use at your own risk.Here is a table made from the formula: the temperature and altitude with give you the correct atmospheric pressure, the numbers below have been pre calculated.

This will give you a good place to start. At this point you can do a plug chop to verify jetting. Be sure you are full throttle under load for at leased yards or so. Up hill works best. If the motor is back firing at decel this is a good indication the pilot jet is to lean. Try richening up the fuel mixture by turning the fuel screw out or the air screw in to allow more fuel. Any more than 3 turns out go one size larger on the pilot jet. Fuel screws are towards the front of the carburetor and air screws are toward the rear of the carburetor.

In most cases screw adjustments won't correct the lean back firing, installing a one size larger pilot jet will do the trick for higher elevations Colorado. Take 0. If it is 80 F at ft, you calculate a new CF, say 0. This gives you a good place to start your fine tuning. Needles are a little trickier, I think each needle clip was worth a change in CF of 0. You can also use it for pilots, but pilots sometimes go the other way larger at high altitude.

You need to determine this by pilot screw position. Another way is by backfiring on a YZF on decel, too lean. Richen up by turning pilot fuel screw out. I have the formula at home, I will get it and post it. I made it into a table and pasted it on the inside of my toolbox lid. Remember, its a good place to start but is not the same as jetting by someone who is good at it.

For example humidity can affect jetting and the formula does not include this. This is your correction factor at standard temperature and pressure STP. So your bike that was jetted for a at STP now requires a 0.

Lets say the main jet that runs best is a The size of the jets within your Holley carburetor will control the flow of fuel from the fuel bowl to the combustion chamber. Holley jets range in size from 40 to 99, with the stock jet size differing based on the carburetor model and engine application.

Holley manufactures each carburetor with a set of jets that will allow the carburetor to perform well at sea level and around 70 degree air temperature. To calculate the proper jet size for your vehicle, you'll need to know your elevation and outside temperature. Establish the elevation and temperature the carburetor will be operating within. Adjust the jets one size for every 2, foot change in elevation or for every 35 degree change in temperature. For example, your current elevation is 2, feet above sea level with a temperature of 70 degrees.

You can calculate that the jets should be increased by exactly one size. If the vehicle will be operated at sea level, but the temperature is 35 degrees, you'll need to reduce the size of the jets by 1 size, as indicated by the stamp on the head of the jet. This article was written by the It Still Runs team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information. To submit your questions or ideas, or to simply learn more about It Still Runs, contact us.

Carburetor help, jetting, and tuning help:

Step 1 Establish the elevation and temperature the carburetor will be operating within. Step 2 Establish the current jet size of the jets within the Holley carburetor.

Tip Each jet is stamped with its size, so adjustments can be made without measuring. References Holley: Jet Information. About the Author This article was written by the It Still Runs team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information.


One thought on “Motorcraft jet size chart

Leave a Reply

Your email address will not be published. Required fields are marked *