-CARBURETOR CONVERSION F.A.Q.-
-CARBURETOR CONVERSION F.A.Q.-
January 9, 2001.
Doing a carburetor conversion on your 4AGE engine is actually rather easy. This page takes a look at what needs to be done for the conversion, rather than talk about the carburetors or jettings themselves. This page will cover three main topics of the conversion:
1. Ignition1. IGNITION
2. Fuel
3. Carburetor Parts
4. Emissions
5. Patience
How to control the engine's ignition without an ECU is the most asked for answer. There are several way to do this, first being the easiest.II. FUEL
- Aftermarket ignition control: Simply buy an MSD 6A(L) or Crane HI-6 ignition box and use the magnetic pick ups from the stock distributor and you will have a working ignition. I have not seen the Crane HI-6 used successfully, but it is cheaper than an MSD 6AL, and comes with a module (pill) less rev-limiter. I personally use the MSD 6A, without rev control. The typical belief of the ignition boxes is that they do not have a built in ignition advance. The 4AGE can run smoothly with around 20-30 BTDC static ignition timing. However, the MSD has a nice built in feature that is not found while reading the instruction manual. By reversing the magnetic leads, the MSD can give you a nice timing advance curve. You simply set the ignition at you want at idle (stock is around 10-15 degrees BTDC). As you blimp the throttle, you will find that the timing jumps to around 20-35 degrees BTDC. For more control over the timing, you can purchase an MSD ignition control box which allows full control of the timing curve.
Another plus feature of going with an aftermarket ignition box is the added spark power (with accompany coil). With carburetion, the fuel is not atomized as well as EFI injectors. Therefore, having a higher power ignition spark can only add power. Don't forget to go with lower resistance spark plug wires as well.
Another way of controlling the ignition timing is an old method of using the distributor internals of a 4K Toyota engine. The 4K distributor uses a mechanical advance, and needs to be transplanted into the distributor of the 4AGE. I have considered this before, but found that a lot of time would be needed to locate a 4K distributor (and money) and then even more time trying to make it work with the 4AGE's distributor. If you decide to go down this path, remember to keep the 4AGE's timing gear or else you will have the timing for a 4K engine trying to work with a 4AGE (not good!).
- Stock ECU: If you already have the stock ECU wired up, there is no need to remove it necessarily. I have heard that the ECU can work the ignition control independently of the fuel system. You might get some error codes because the injectors and stock EFI manifold will be disconnected. This would be a cheaper way of doing the ignition. I have not seen this work personally, but theoretically, it should work.
If your car was originally carbureted, fuel delivery is simple. All you need to do is get a low pressure (around 5 PSI) electrical fuel pump, in-line fuel filter, a fuel pressure regulator (very important, make sure you get a good one), and a fuel pressure gauge to make sure you are getting right pressure setting. Place the devices in this order: pump - filter - regulator - pressure gauge.III. CARBURETOR PARTSIf your car is equipped with an EFI fuel pump, there are two paths to choose from.
Do not forget that the stock EFI's injector holes are not located on the removable intake manifold, but on the head itself. You must block these holes off, or you will have a severe vacuum leak. I used liquid weld (comes in two tubes, all you do is mix it together and let it set) to seal the holes. There are many methods to seal these holes, so take your time and figure out which is best for you.
- First would be to keep your high pressure pump (EFI pump), run a "Y" joint at the exit of the high pressure fuel line, route one line to a pressure regulator (to get pressure from 40-50 PSI down to 2 - 3 PSI), and use the second outlet as a fuel return line. This way the regulator and the pump will not have excessive pressure built in.
- The second method would be to remove the stock fuel pump, or leave it in the tank, but disconnected, and instal an in-line low pressure fuel pump. The "dead" fuel pump will not black the fuel, it will simply act as another piece of fuel hose.
This is what I needed to get my Webers to work:IV. EMISSIONS
- 2 side draught carburetors
- manifold
- linkage
- air filters
- anti-vibration mounts (sandwiched between manifold and carburetors)
- "Uni-Syn" or similar carburetor synchronizing tool
- proper jetting
Or the lack of. Side draught carburetors have no emission reduction systems. Meaning if you have a U.S. spec 4AGE, you must close up the EGR hole on your exhaust manifold. Also, your crankcase breather valve should be capped off with some sort of filter to prevent engine oil being sprayed everywhere. Be sure to check with your state's laws before attempting to do a conversion.V. PATIENCE
This is key. It will take quite some time to get everything running correctly, and to learn how your side draught carburetor works. It took me roughly one year to hunt down all the major bugs. At the time of writing, I'm still struggling with minor issues such as achieving smoother progression from idle to main circuits.Here are some pointers I learned that will make life a little easier for you:
- Never buy used carbs. Get clean, new carbs that have very sensitive throttle plates and other equipment set from the factory. Used carbs can cause engine fires, don't ask how I know this.
- Make sure all your other systems, such as fuel delivery, ignition, and exhaust are set and installed correctly before attempting to tune the carburetors.
- Buy a Weber book (I recommend Weber Carburetors by Pat Braden, published by HPBooks, if you can't find that, get a Hayes Manual from a local autoparts store about Weber Carburetors) and learn how the carburetor works.
- There are several different types of linkages available, through experience, I've found that getting a top mount linkage control directly from Weber is best. Avoid rod and lever arm type linkages; they are prone to distort your synchronization from vibrations. The top mount linkage actuates both carbs directly in-between them, meaning that there is little moving pieces from one carburetor to the other.
- Expect jets to come to a startling total. They are precision parts and in the case of Webers, come from Italy, you get what you pay for. Also expect to have a library of jets by the time you find the correct jetting for you car.
- Never over tightening any carburetor bolts, they do not need a tremendous force to keep them from falling apart.
- Lastly, REMEMBER TO KEEP A FIRE EXTINGUISHER IN YOUR CAR, just encase.