I typed up just about all of the information I have learned about the 22R Aisin carburetor. I knew very little about carburetors when I first got my '86 Toyota Pickup. Many trail fixes and tweaks to get the truck running again has given me confidence and experience with it. If my engine will not start or dies, I am no longer afraid as I know and understand the carburetor and don't have to mess with any of that EFI stuff. I had never been inside a carburetor before I rebuilt mine.

If you are in the same position, don't worry about it - its not as scary as it sounds. Carburetors are really very simple in the way they acomplish their job - to provide the correct mixture of air and fuel to the engine. I hope this site helps give you a basic understanding of the 22R Aisin carburetor so that you can have the confidence to fix/tweak whatever may be wrong with yours. While there is lots of advanced info about the carb on this site, I tried to assume a very low/beginner level of understanding. I chose the topics based problems I have encountered in person, as well as questions I have seen/answered on forums.

 

 

*all diagrams are taken from an '85 Factory Service Manual

 

Aisin Carbs on Angles/Offroad

Many people say EFI is better than a carb offroad because a carburetor does not run so well on extreme angles. This is not necessarily true. First of all, unless you're in a truggy, before you're at a side hill too extreme for your carb, the truck is rolling over. The pitch is what you need to worry about. A 22R carb will run fine on the steepest downhill; but has trouble on steep uphills.

This is because when the carb is tilted back, too much fuel is dumped down the intake. There are a number of things to solve this. One option is the flip the carb around, but of course then it will have trouble running on down hills. The easiest and most practical option is to run an overflow line from the overflow port above the driver's side choke plate leading away from the carb. If you do not do this, then when the carb is tilted back the float bowl overflows through this port right into the venturi of the carb. This floods the engine causing it to stall. To make the "greenies" happy this line should be run into a container of some sort so gas is not dumped on the ground (not much gas at all comes out though). The thinner the line the better in order to allow maximum air flow into the carb.

Some other things that help are to lower the float level slightly, add a fuel pressure regulator and install an MSD ignition. Lowering the float level will put less fuel in the bowl making it harder to overflow. Adding a fuel pressure regulator will slow down the rate at which the float bowl is filled with gas. An MSD ignition will give you a hotter/longer spark, enabling you to burn a higher quantity of fuel that is dumped into the intake. This will also help re-start the engine if it does stall due to flooding.

One other important thing to note is that it is absolutely imperative that you have an air filter, and that it is snug against the top of the carb. I used to have carb trouble every time I went offroad. My truck would just stop idling and in general came off idle like crap. I discovered that although I had an air filter and assembly, it was loose and could bounce ½ cm off the top of the carb. Mud was getting in here and clogging my idle jet. I'd have to take the top of the carb off and clean it out each time. Make sure your air cleaner is snug on the carb and maybe even use some rtv to seal the joint

 

Auxiliary Accelerator Pump Diaphragm (AAP)

The auxiliary accelerator pump diaphragm (AAP) is located at the front base of the driver's side of the carb. It has three screws and one vacuum line.

To check if it is bad, simply pull off the vacuum line and look and smell for fuel. If there is gas in the line, the diaphragm is punctured or cracked and should be replaced. I have heard of people simply plugging the vacuum port and being fine, although your idle/take off may stumble a little when cold.

All the AAP does is squirt a little extra fuel into the mixture when the engine is cold. It has no effect on the engine when warm - even when not working properly. The AAP is vacuum operated - when vacuum is applied the diaphragm opens which then adds a little extra fuel. The vacuum is applied by the BVSV which is screwed into a water jacket on the head. This senses the temperature of the coolant and applies or does not apply vacuum to the AAP.

A new diaphragm comes with any rebuild kit or can be purchased from the dealer and maybe from some aftermarket parts stores.

 

Charcoal Canister(s)

The charcoal canister(s)'s job is to vent the gas tank. Basically the worst that will happen if they are clogged is when your tank gets near empty and you undo the gas cap, you will hear a whoosh of air go into the tank. This is because a vacuum is created in the tank as gas leaves and no air can enter through the canister due to it being clogged. You can usually blow the canister(s) out with air to unclog them.

I have never heard of a clogged canister affecting fuel delivery to the engine on a 22R. My canisters are pretty clogged with mud (I cleaned them once and they clogged back up) and I hear air entering the tank every time I go to put gas in it. However, I notice no change in performance so I just let it be.



Choke Breaker Diaphragm

This diaphragm barely opens the passenger side choke plate shortly after the engine starts. This is to lean out the mixture a little as it does not need to be as rich as when the engine was starting. The engine will run fine without this diaphragm working.

 

Choke Inspection/Adjustment

Inspection:
Most carburetor problems are related to the choke. There are two choke plates on top of the carb. Generally you don't have to worry about the driver's side plate as it is vacuum operated and only opens under high vacuum (full throttle). However, I used a small rubber band on the linkage to open the driver's side plate 100% of the time for more air flow. This had no ill affects during cold weather, nor did it give me any more power...

The passenger side plate is what you need to be concerned with. The electric choke coil keeps this shut when cold. When the engine starts, enough voltage is applied to the choke coil which contracts, moving the choke plate lever which slowly moves the choke plate to the completely vertical position. If the ignition is on but engine off, there is still voltage applied to the coil but not enough to contract it. Once the engine starts and the alternator kicks in, the correct amount of voltage is applied to the coil and it begins to contract.

The engine must be completely cold to make sure the choke coil is working properly. Take the air cleaner cover off the carb. Punch the gas pedal to the floor to engage the fast idle cam/choke. Look at the passenger side choke plate - if you engaged the choke correctly it should be mostly closed (~1/8 th of an inch open). If it is not, you may have punched the gas pedal incorrectly or your fast idle cam linkage needs to be cleaned/lubricated with carb cleaner and wd-40.

To verify that the choke is engaged correctly (this does the same thing as flooring the gas pedal):
With your hand, slightly open the throttle cable (about ¼ throttle is fine) and at the same time close the passenger side choke plate with your finger. Let go of the throttle while holding the plate as far closed as it will go (this sequence has the same effect as stomping the gas pedal before starting the truck). Let go of the choke plate and if your choke is closing correctly then the plate should be about 1/8 th of an inch open. If you open the plate with your finger it should spring back to the closed position. If it does not spring back when pushed open, your choke needs to be adjusted or your coil needs to be replaced.

Now without touching the gas, start the truck. It should idle at the cold idle speed as the fast idle cam/choke is engaged. If you wait a minute or two the idle should step down to the warm idle speed as the choke opener kicks in. The same should also happen if you punch the gas pedal - your idle should drop to your warm idle speed within a couple of seconds. Now go look at the choke plate. It should slowly open as the engine warms to operating temperature until it is completely vertical. Once vertical if you try to close it with your finger, it should spring back to vertical. If it does not open to vertical or spring back when pushed closed, your choke needs to be adjusted or your coil needs to be replaced.


Adjustment:
If you're lucky, the choke coil is held on by three screws. If you're unlucky there will be three pop-rivets, in which case you will have to drill them out and thread holes for screws.

If you must remove the choke housing because you have pop rivets, or for some other reason, pay VERY close attention to how the linkage/spring inside is setup. It can be tricky to put back together. Just remember, the coil contracts as it heats up which opens the choke plate.

The engine must be cold to adjust the choke. Use the previously mentioned procedure to engage the fast idle cam/choke. If you have screws, then only loosen them until you can rotate the choke housing. Rotate it until the choke plate is only about 1/8 th of an inch open, and re-tighten the screws. Again, use the above procedure to verify that the choke opens to the vertical position correctly. If you cannot adjust the choke so that it closes or opens the correct amount, you most likely need a new coil.

According to the FSM, you can measure the resistance of the choke coil to make sure it is within spec: 19-23 ohms at 20*C (68*F) from the choke coil wire to ground.

 

Choke Opener Diaphragm

This diaphragm slowly disengages the fast idle cam which in turn opens the passenger side choke plate. The choke opener, like the AAP, is also controlled by vacum from the BVSV. This diaphragm is not necessary as you can acomplish the same exact thing by punching the gas pedal when you wish to disengaged the fast idle cam.

 

Fuel Filter

The fuel filter is very simple - it has one in and one out. It is located right near the gas tank clipped to the inside rail of the frame. Just follow the lines coming from the gas tank and one will lead you to the filter in a few feet of fuel line. This should take you a few minutes to replace.



Fuel Pump

These simple mechanical pumps rarely fail. Since the pump is right near the carb, it sucks gas from the gas tank - there is no electrical pump inside the tank pumping gas to the carb. A stock mechanical fuel pump puts out ~7psi, but can be regulated to about 4psi for better offraod performance.

 

Idle Fuel Cut Solenoid

The idle cut solenoid's job is to cut gas flow to the carb at idle with the ignition off. This is to prevent your engine from "dieseling" (sputtering to a stop) when you turn your key off. I have noticed my engine to do this if I rev it real high and then turn the key off. Since there is still a lot of gas flowing through the carb, the engine continues to sputter for a few seconds before it finally dies. The idle cut solenoid does its best to stop this.

The solenoid has two wires going to it. One is the black ground wire and the other is the white with black-striped power wire. When you turn your key on, this power wire goes hot which opens the solenoid which opens your idle jet. If your key is off or your solenoid is bad, then the solenoid is closed as is your idle jet. Your engine will NOT idle for more than one second if this is the case. Of course the solenoid can become stuck open, which may cause your engine to diesel.

To test the solenoid, simply ground the black wire and apply voltage to the white/black-striped wire. You should here a very faint click from the solenoid, similar to the click of a mechanical pencil. If you don't here a click then the solenoid must be replaced.

Replacing the solenoid is straight forward - the solenoid itself is basically a bolt if you look at it. What makes it a little tricky is the fact that its two wires are connected to the same green connector as your choke coil and outer vent control valve (I don't know what this does but your carb doesn't need it to run). Probably the easiest thing to do is to cut the two solenoid wires and splice in the new one. Otherwise, you must replace the choke coil at the same time and the choke coil can be a little tricky and is better left untouched.

 

Idle Speed/Mixture Adjustments

There are four screws on the passenger side of the carb - warm idle speed, cold idle speed, idle mixture and ac idle up. Each one has set specifications and you can tweak them from there to meet your wants/needs.


Warm Idle Speed:
Once the engine has reached operating temperature, at idle, punch the gas pedal to make sure the carb is off of the fast idle cam linkage. You may notice the idle rpms drop slightly (which means you just stepped off the fast idle cam); or no change at all, which means the cam was not engaged. Turn the adjusting screw clockwise to speed up the rpms and counter-clockwise to slow them down.

Factory spec is 700rpms for M/T and 750rpms for A/T, but you may want to set it higher for offroad or an aftermarket camshaft. I prefer 900-1,000rpms for offroading and EB's (www.engnbldr.com) 268* camshaft.

Cold Idle Speed:
With the engine cold, floor the gas pedal once to engage the choke/fast idle cam. Verify that the fast idle cam is engaged by slightly opening the throttle and pulling up on the fast idle cam linkage (you may need to take off the air cleaner to get your hand to the linkage). Without touching the gas pedal, start the engine. Turn the screw clockwise to speed up the revs, and the opposite to slow them down.

Factory specs for the cold idle speed are:
•  1981-83: 2,400 rpms
•  1984-86: 2,600 rpms
•  1987-88: 3,000 rpms.

Again, you may want to tweak these based on your preference/engine, but this is not as important as your warm idle speed.


Idle Mixture:
From the factory, there is a cap over this screw to prevent the screw from backing out due to vibrations. If the cap is still there, most likely you do not need to touch this screw. If the cap is gone, then the carb has been rebuilt or someone was playing with things that shouldn't have been played with. Since the screw WILL back out over time, put a dab of rtv on the threads to prevent this from happening.

To reset the idle mixture screw for a 22R:
•  1982 - 2.5 turns from fully closed
•  1983-88 - 4 turns from fully closed.

These of course are baseline settings and will probably need to be tweaked ¼ or even maybe ½ a turn depending on your engine/timing, etc. You want to set the idle mixture first to obtain a smooth idle, and then set the idle speed second to where you prefer. This can generally be done just by tweaking the screws ¼ turn at a time, but the procedure to do so is:

With the engine at operating temperature, turn your idle MIXTURE screw until you obtain the fastest idle speed possible. Then set the idle speed screw to where you would like it (factory specs or higher based on preference). Repeat these two steps until the mixture screw cannot speed up the idle. Then use the idle speed screw to set the idle to where you prefer.

 

Jets




1) Slow jet
2) Power valve jet
3) Metering needle guide
4) Secondary jet
5) Primary jet access plug
6) Primary jet

 

The stock jets are fine in just about all circumstances. I don't think there are any re-jet kits for the aisin carbs, but I do know that a weber main jet screws into the aisin primary jet slot. The general consencous I gather is that its not worth the trouble to re-jet these carbs.

 

Rebuild Kits

Many people ask what the difference is between the $16 AutoZone kit and the $40 Napa kit. The answer is the cheap kit has generalized parts for all 22R carbs. The more expensive kit has more parts for the specific carb you purchase it for. If the parts guy asks you for your OEM carb number then you're getting the better/more expensive/more specific kit. If not, call somewhere else. The carb number is found on a tab on the front most screw, on the driver's side, holding the top of the carb to the base of the carb. If the screw is not there, most likely the carb was at one point rebuilt.

The rebuild kit should come with instructions - my Napa kit did. This will include an exploded diagram of every single part of the carb - there are a lot. All the kit contains is the four diaphragms, gaskets and a new jet or two. The main purpose of the rebuild is to disassemble the carb and soak everything in cleaner so that all the passages get cleaned out. This will make the carb feel brand new once re-installed.

Since there are a lot of parts, I got a cheap muffin tray and whenever I took a part off, i put it in a spot in the tray. I then labeled the part with the number it was listed as on the diagram. This made reassembly 100 times easier. Taking a picture or two of the linkages will also help.

 

Diagrams

 

Federal/Canada:


 

California:

 

Exploded View:

Web Resources

  • 4x4 Wire - the best 4x4 and Toyota forum on the web!
  • AutoZone Manual - online manual which has lots of information about Toyota carbs/Toyotas in general.
  • Factory Service Manuals - The '85 FSM has TONS of info about the Aisin carb (when you get to the forum thread, right-click the '85 FSM link and save as)

If you would like to ask a question not covered in this or think something should be changed, feel free to send me a private message on 4x4wire.com. My username is "Scerb"