I think once someone actually gets an EFI zilla built you're going to see a lot more of them 

EFI would be bad ass, But I think its going to be alot of work to make it proper. Carbs have been solid for decades, I would stick with em.

I'm all for progress & such. But to me, it seems like one more thing to break when i'm in the worst possible spot.

A local shop (KD Cycle) has a CR-500 powered ATC-250R that has efi. The problem with this bike is that it's just a one trick pony. The owner said he prefered the carb for dune riding but the efi was the hot ticket for the 300' sand drag track.

It's not practical for an efi system to be installed on a 25 year old two stroke engine. The injection systems that are used on two strokes engines today require TBap sensor, exhaust temp sensor, crank position sensor, engine temp sensor and and a control unit with a very intraget fuel/ignition mapping. That requires a stator that can supply sufficient power. Not to mention the only big gains would come from a direct injection that requires injectors to be installed directly in the transfer ports. Cylinder disgn and port setup changes dramatically with a setup that would give you any tipe of big gains. Fuel injection is very temperamental with mods. If you start changing pipe set ups, port timing, even a open airbox. The control unit would need reprograming or a piggy back control unit. Sounds good but not practical.

Yes your right it would need rejetting. My point was the cost to have a piggy back or program equipment. Also with 2 stroke fuel injection engines used today they are not close loop systems. That's what makes them so temperamental to mods. You can't run O2 sensors because of the oil in the fuel. The exhaust gases will kill the O2 sensor in about 15 hours of run time.

Austen, you would need a lot more than what you listed. Injector, throttle body with tps, not just air temp but air density and pressure. You need a fuel pump to supply fuel pressure to the injector and everything else I listed above. Fuel mapping from scratch wouldn't be fun. Again not practical.

Motor geek - on the ecu's you were involved with, what manufactures were they?

Where they mapped on throttle position vs rpm or boost/vacuum vs rpm?

Chuck D - I agree with your comments but if you made and changes to a carb'd bike engine it would still need rejetting

The engine already has a crank sensor fitted to work the electronic ignition, all I can see that would be needed to work the ecu would be throttle position sensor, air temp, water temp and possibly map sensor and a battery with charging system.

Injection Research Specialist, Echlin Engine Systems, Pacer Industries, EFI Technologies, and Electomotive Industries, were some of the companies that I was involved with. 

IRS, Echlin and Pacer were primarily aiming to supply the two-stroke snowmobile and jet ski industry.  EFI Technologies was one of the pioneers in EFI for Cosworth and Ilmore Chevrolet Indy Car engines as well as Buick GTP engines.  EFI Technologies wanted to get into the two-stroke engines market.  EFI technologies teamed up with Wescoast Performance. Products. Westcoast worked on the project for about a year and then came to me for help.  Electomotive was a company that supplied controllers for the automotive hot rod industry and also wanted to get into the two-stroke market.

We tried the Alpha N (throttle position vs RPM) and the Speed Density (Manifold pressure vs RPM) as well as a combination of both systems.  Alpha N systems were the best systems on most two strokes with one throttle body per cylinder.  Speed Density did not work very well on the one throttle body per cylinder because of the weak vacuum signal.  On multi-cylinder engines that had all of their intakes connected to one common plenum with one throttle body, Speed Density systems showed a flicker of hope.

The airflow into the engine follows the tuned length of the pipe on a two-stroke.  The tuned length of a two-stroke pipe is not fixed.  The tuned length depends primarily on exhaust temp and the density of the exhaust. The density of the exhaust depends upon the ACTUAL air/fuel ratio of the by products of combustion and not what an O2 sensor “sees” and the trapping efficiency.  An O2 sensor only "sees" oxygen and does not see raw fuel or any other gas that may be present.  A O2 sensor will see a rich miss-fire as the most lean condition possible!!!!!!!!!

Many versions of mass flow sensors running in closed loop with different plenums sizes between the engine and the mass flow sensor were also developed.  It required huge volume plenums to damp the extreme amplitudes and the reverse flow from the two-stroke intake process.  The optimum plenum sizes were not practical for the vehicles the engines were to be used on.

The alpha N system requires the engine to always consume the same amount of air at a given RPM and throttle position and corrected by barometric pressure, intake temp. and engine temp.  A four-stroke’s engine volumetric efficiency repeats the above process very well.  A highly tuned two-stroke engine will not consume the same amount of air at a particular RPM and throttle position each time it returns to that same throttle position and RPM. because of the inconsistency of a tuned pipe.  I learned how to test two strokes long before the inertia dynos became popular and anyone with $15,000  to $20, 000 in their pocket can become an instant expert on dyno testing and tuning  This is one of the reasons that I use heavy rollers on my chassis dyno and I my experience  will not allow me to become one of the sheeple that follow the recommendations of the dyno manufactures on what type of dyno should be used to test two stroke engines with highly tuned pipes. 

Most of the EFI development that I was involved with was about 20 years ago.  We now have faster processors and the diesel industry has technology like the ultra high-pressure electronic injectors and pumps that might have some application for two-stroke EFI.  We still have to solve the age-old problem of predicting the airflow into the engine and knowing the exact amount of air that got trapped into the combustion chamber so that we can fuel it properly. 

The direct injected two-strokes are not simple two strokes.  The direct injected two-strokes are very expensive to build and repair.  We still need to figure out how to fuel inject two-stokes to reduce emissions and keep them simple or face extinction. 

That kit is a close loop system. o2 sensor do not work with two strokes, unless you plan on replacing the sensor every 15 hours.

Would love to see a efi lt500 on a dyno and what kind of hp can you see out of it

Perhaps you need to read my post again, I never said anything about running an open loop with an O2 sensor.
If an open loop system has an O2 sensor then it's not open loop anymore.
Like I said before, longevity with an O2 sensor is being extended in 2-stroke environments by using an air oil separator.
Unless your bung extender had an air oil separator, I wouldn't expect it to last very long either.
You can't just weld a bung on your exhaust and expect the O2 sensor to last forever...but advancements in O2 tech are going to change that in the near future.

The point I was trying to make that you seemed to have missed was that most EFI quads are open loop and have never used an O2 sensor during their entire existence.
So the fact that an O2 sensor won't work well in a 2-stroke environment is overshadowed by the fact that EFI quads are being run without them on a daily basis.
I've got an open loop EFI setup on my LTR right now, and I can promise you there is no O2 sensor on it.

What people don't understand about open and closed loop systems is that they think an open loop is no better than a carb is at metering fuel for varying atmospheric conditions.
An open loop system can go from sea level at 70deg or 9,000ft at 20deg and KNOW the difference between them.
A carb isn't able to discern the difference, which is why everyone has slightly different jets in their carbs depending on all sorts of factors.
Open loop systems can determine air density from their sensors just as well as closed loop systems can.
Both systems have to be told what to do at those conditions with the fuel map, so they're only as accurate as the tune they receive.
The difference being that a closed loop system can double check to be sure the tune is in keeping with how you expect the A/F ratio to react to that portion of the fuel map.
There's a certain amount of adjustment leeway that you can give a closed loop system to correct on its own, but give it too much leeway with a poor fuel map and it'll hunt the A/F ratio without ever getting it nailed down.
Basically, the closed loop system is only there to accommodate the variables that can't be accounted for with standard sensors.
Things like an injector that's performing a little sloppy, or an ignition coil that's getting weak, running it in densely forested areas (slightly higher O2 saturation) vs. a desert, weak reeds, weak piston rings that lower compression, etc.
Those are things that you can't program into a fuel map, but the O2 sensor will catch.
We're not talking about a whole lot of change here though, it's just not running at an optimal level at all times without the O2 sensor giving it some feedback.

Tuning an open loop EFI is just like tuning a carb, only with a different medium.
If you run a certain set of jets and needle position for winter riding, then run a different set of jets during the summer, then another set for riding in a different area, you still have to tune for each of them.
If you were to take all of your tuning notes (writing down main jet, idle jet, needle position, etc. etc.) in a notebook, you could simply refer to that notebook to rejet for winter, or wherever.
With an EFI, you tune the fuel map with the conditions you're presently seeing and it remembers your tuning.
Come back to it a few months later when the temps have changed and tune it again (just like you would with a carb) and it remembers that tune as well as your previous tune.
Go to your favorite riding spot which has a 2,00ft elevation change and do some tuning there (just like you would with a carb) and it remembers that tune as well as the other two.
Pretty soon, you're going to have a lot of tuning info that the EFI can choose from depending on what the sensors are telling it.
If you're at home, and the density altitude changes drastically enough to mimic the riding spot that's 2,000ft above you, the sensors will detect the density change and adjust tuning as needed.
You may not have every tune for every situation, but you'll be able to see a trend in how the fuel map changes as pressure and temp changes, and smooth the map out.
It may not run great when you get between the points that you've mapped, but it'll be close enough that you won't spend very much time mapping from scratch, only some small adjustments here and there to detail the map even further.
So what you're basically doing with the EFI fuel map is jotting down all of your tuning notes into one computer that doesn't wait for you to say "Hey it's winter, maybe we should up the main jet a size" it just automatically does it for you as soon as those conditions are met.

Here's one reason why I want to see someone install an EFI on an LT....a fuel map is downloadable.
If someone went through all the trouble of tuning their LT and getting it down perfectly, they can email that file to the next guy who wants to try it.
It'll be off, of course, but you'll have a generic base map to start with and fine tune to your bike, lessening some of the time it takes tuning from scratch.
If enough guys get together and start a little database of base maps grouped by different engine mods (like bone stock engine, stock with FMF pipe, stock with Q pipe, etc.), then the tuning time is cut down even more.
People can find a fuel map that was made for a bike with the same mods and have a much better chance at success the first time around.
Fuel mapping for density altitude extremes (like really high altitudes or extreme cold) that most guys normally will never see could be tuned by someone who lives in Colorado or an ice racer in NY to fill in the edges of the fuel map for those of us who will likely never see those conditions to map ourselves.
It's more of a pipe dream than anything, seeing as how there's so few of us LT owners out there, and an even smaller group that might be interested in EFI, and an even smaller group that would be good at tuning an EFI, and an even smaller group that decided to run a particular ECU...you get the idea.
That would be pretty sweet though, a big database of fuel maps that you could pick and choose from, tweak it a bit here and there, and you've got an EFI that's tuned for all sorts of conditions that you'd probably never get a chance to see.

Would love to see a efi lt500 on a dyno and what kind of hp can you see out of it

EFI or mechanical fuel injection will not make any more power than a carburetor that has identical air flow characteristics when the carburetor has the correct main jet.


 EFI should provide better fuel mileage and be self-correcting for temperature and altitude if the programmer has done his homework. 

Automobile manufactures spend more time than one afternoon in the dyno room building fuel and spark maps. 

Some of the theoretical corrections can be done by math.  The real home work has to be done in the field by testing the engine at all of the extremes; extreme cold, high altitude, high humidity, etc and everything in between and then use the real world corrections if they are not in agreement with the theoretical generated corrections. Unfortunately engines do not always operate according to theory.

It'll be a lot easier to tune an EFI on an aircraft, since you don't need a dyno for it to produce 100% power, or anywhere in between.
All you have to do is tie it down or hold the brakes and give it throttle.
The hard part is tuning for altitude...I'm not sure how comfortable you'd feel hooking up to the ECU and making changes to it while you're 8,000ft up.

Oh sweet, that'll make things easier.
Rotax aircraft engines are highly neglected in the pipe and porting dept., a guy could make a killing selling top notch pipes for them.
It would also be pretty simple, since an aircraft engine has a certain target RPM range for flight...or hovering, in some cases.
Tune the pipe for a specific engine RPM and don't even worry about low and mid range that'll never be utilized.