That's what concerns me. It appears that the microsquirt only has 2 fuel outputs, so I'd have to go megasquirt.
From what I can find, batch injection should work well enough on a 4-cylinder. It sounds like the only way sequential would be better is if you tune each cylinder individually. But you need a ton of sensors (individual EGT and O2 per cylinder) and dyno time to be able to see that benefit. It seems like you'd be fine with a simple tune using a single O2 sensor.
www.diyautotune.com/support/faq/megasqui...tial-fuel-injection/
www.msextra.com/forums/viewtopic.php?t=57746
www.enginebasics.com/EFI%20Tuning/Batch%20vs%20Sequential.html
The microsquirt (from my understanding) has 2 spark outputs with a possibility of 4, but only has 2 fuel outputs. It seems as though I would need a 4 spark outputs, 1 for each spark plug and a 4 fuel outputs, 1 for each cylinder.
Technically, you don't even need to touch your ignition system. If the factory stock ignition is working fine, leave it alone. You're trying to replace the fuel system. They are separate with carbs, and can stay separate with EFI. But you will need to figure out how to get the crank trigger signal into the microsquirt (or whatever ECU you use). You can always go back and add the ECU controlled ignition later once you get the fuel system working.
As for fuel, it looks like the microsquire can do the job. But you'll need a lot of other parts.
What would you use for the throttle body and injectors? The most direct fit solution would be to get a set of throttle bodies from a GPz750 Turbo or a GPz1100. The cylinder spacing is correct, the assembly includes injectors, and some of them have a throttle position sensor that may be useful or at least could be adapted to work. But watch out for the early GPz1100 throttle bodies. Those bikes had injector ports cast into the head and would be pretty useless for your use.
ebay.com/itm/225118215430
ebay.com/itm/363791914487
Do you have fabrication skills. You could fabricate a manifold and plenum and get an automotive style single throttle body. But making the injector ports would be some real work. Certainly more complex than the tubes and boxes part of the manifold. I suppose if you have a common plenum you could do throttle-body mounted injectors...
speed.academy/how-to-fabricate-a-custom-intake-manifold/
hremanifolds.com/
www.hogansracingmanifolds.com/custom-int...om-intake-manifolds/
www.wilsonmanifolds.com/products/custom-billet-intake-manifold
Next you need a fuel pump, fuel pressure regulator, some plumbing to get the fuel to return to the tank, and wiring for the pump.
And you'll need to weld a bung in the exhaust for the O2 sensor, and figure out how that's all wired. Also, the throttle position sensor on the early GPz bikes was a bit crude. You might need to adapt a modern one to the TPS mounting location.
Another reason why you might actually
want to use batch fuel injection is that I believe sequential injection requires that you add a cam shaft position sensor. The crank sensor isn't enough. With the crank sensor alone the computer doesn't know which stroke the cylinder is on. All the crank sensor tells the computer is the location of top dead center, but it could be the compression stroke or the exhaust stroke. The cam sensor allows the computer to know when to fire the injector. Adding a cam position sensor is not easy. I think you'd have to fabricate a sensor mount on the cam cover and figure out how to attached a wheel or magnet to the camshaft.
What else? I think you also want an engine temperature sensor. The injected GPz bikes had a mounting point in the cylinder block for a temperature sensor.
Then it come to tuning. I've heard that short individual throttle bodies make it very hard to get a good signal for manifold pressure (MAP). It's also tricky to use an air-flow meter (MAF), as you'd need four of them, or one on the air box? I think that often leaves just Alpha-N fueling. Alpha-N is kind of a best guess for how much fuel is needed, based on only throttle position and engine speed. But it doesn't really adapt to load (up hill or down hill) or atmospheric changes (temp, humidity, pressure). I believe this is essentially how the GPz110 unitrack was set up, so it can work, but lots of folks replaced the EFI with carbs on those bikes.
I've wanted to do the EFI conversion for a long time. But it seems like a TON of work so I've never done it. Maybe someday.