Originally Posted by
ps2fixer
It's possible and could be adapted from a newer quad likely. Basically what you're talking about is EFI, or fuel injection. Like for car talk, the Toyota pickup from 1985-1988 had a carb option, however it still had an O2 sensor, temp sensor etc, but wasn't self learning because it had no way to adjust the carb electronically. The trucks that came with EFI of course were self learning and the ECU was much more complex since it did so much more.
EFI is kind of a double edged sword, it's awesome in the face with a programmable ECU you have a lot of control with timing, air fuel ratio etc, but there's so much more that can go wrong with sensors etc that could render the machine dead on the side of the trail.
If I was wanting to go EFI, I'd target a 650/580 rincon or similar machine to snatch it's EFI system from. Mod the intake to fit say a 350x, figure out how to mount the engine temp sensor so it's somewhat accurate (water cooled vs air), and trick it into not caring about the transmission shift solenoids not being connected (like taking an automatic car ECU and putting it into a manual, I've done that once, but the truck ran/functioned fine so I didn't care about the check engine light, no inspection in this state).
Anyway, I'd say the EFI system would benefit over the Carb builds since it can adjust timing etc based on temp, so it can have prime tuning at full operating temps with no concern with how hard it is to start etc. In theory it should be more responsive too, big time since there's no accelerator pump on our carbs.
Basic requirements off the top of my head for an EFI system is listed below, might miss something but gives an idea what sensors would be needed.
ECU/Brain of the operation of course
Air intake metering (so it knows how much gas to give the air charge)
Fuel injector(s)
O2 sensor (to make sure the tuning is burning correctly and at the right air fuel ratio)
engine temp sensor (cold vs hot needs are different, aka so "choke" can work in the EFI system)
crank/cam sensor (so the ECU knows when to spark etc, basically the same setup as what a CDI does, pulse generators might even work already for this need)
Coil might have to be changed, depending how the ECU fires it, it's more of a computer, so it doesn't have raw power running though them normally, like our CDI's do.
Throttle positioning sensor - this tells how much gas you're giving it, so if you go from a low rpm and floor it, it can give extra fuel charge to make up for the sudden vacuum loss. It also can cut injection when going from high rpm to idle to save fuel, most modern cars do this when engine braking in gear.
I think that's about everything, of course you have to power the ECU off 12v, so you would probably have to add a DC power kit and battery if the machine doesn't have a battery factory. This also means likely a dead battery = no start. If I recall correctly the Rincon does have a pull starter though, nearly impossible to start off it though I bet. I know the 450 foreman (carb for the one I have experience with) is a heck of a pull to get going.
Probably should mention, the EFI systems don't really care how big or small an engine is, but going smaller than design makes it harder to meter the fuel as accurately for the over sized injector(s), same goes in reverse, going bigger than designed hits the limit of the injector not keeping up at high rpm/max fuel charge situations. The biggest thing to have accurate is how much air is flowing into the intake and it will adjust accordingly. Matching engine cc size would help keep it more accurate though. Changing the injector(s) might throw off the ECU map, but matching the engine size might make it more correct than having the oversized injector(s).
Oh another spot to look for EFI systems could be modern motorcycles. First one that came to mind that probably wouldn't be a first pick is the 600rr bike, it has dual sets of injectors and multi cylinder so kind of a different beast from what our 3 wheeler engines are deigned after. Would make a wicked fast 3 wheeler with that engine in it for in a straight line race with the 110hp or so and if I remember right 15k rpm red line.
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