248 replies to this topic

[grayracer513]

HeadTrauma said:

What is your definition of the "right" time to inject fuel? If you're only controlling fuel and leaving the stock ignition alone, then you can tailor the injection point to just about wherever in the cycle you want by changing the trigger position. However, like we have said, the actual injection point is not that important.

The first automotive EFI sytems were "batch fired", that is sets of multiple nozzles were fired simultaneously whether it was time for the intake cycle on a particular cylinder or not.  The worst example (and I mean worst in the literal sense) of this is the "throttle body injection" units that appeared on some stuff out of Detroit in the eighties, but those are nothing more that electronic carburetors, and should be forgotten as quickly as possible.  For the most part, batch firing was done with port located nozzles in sets of at least half the cylinders in the engine.  The fuel delivered early simply piled up in the intake port.  The most effective way this was done was to provide the same total number of shots as the number of cylinders in the batch, so that if it was a V8 with two batches, each batch would fire four times, each shot being a quarter of the amount needed.  The one that happens during the actual intake stroke serves to "stir up" and re-atomize the earlier deliveries.

By 1990, this was nearly obsolete, and the best EFI systems available from GM in 2000 could control each firing of each injector and spark plug for each individual combustion event entirely independently based on current sensor output in real time up to the cut off at red line.  

The point in this is that there is an ideal time to fire the nozzle, but there is also a considerable amount of leeway between ideal and entirely serviceable.

[BillDozer TT Newbie]

Thanks HT. I've got your point and I appreciate all of your input and effort. Ill go ahead and try it with the injector pulse off of the coil pack signal. If that doesn't work, I will just buy a GM CAS and bore a hole in my nice brand new engine cover and stamp the flywheel so that the signal comes at the IDEAL time. I guess what your saying about the timing of it all makes sense because the atomized fuel will just sit there till compressed anyway. I would just want her to squirt right before the piston was heading back up to TDC. I just never saw logically how the machine would run with the injector just firing away at random.

[smcdonn TT Gold Member]

Another point is that a correctly sized fuel injector can't flow enough fuel to only inject during the intake stroke.  At max power your dwell time will be around 80-90% which is much longer than the time you have to inject just during the intake stroke.

[HeadTrauma Get Help Now]

Another very good point.

[BillDozer TT Newbie]

Right on. I figured out the fuel pump. Im going to use a 2008 Suzuki LTR pump. It sits outside of the tank like an inline Walbro but it has a built in return system on it. Its a dead head setup at the injector but theres a flow regulator built right into the pump. The LTR throttle body should work nicely aswell.

Again, thanks guys for all your info. HT, I wasnt trying to give you shit, it just sometimes takes me a while to figure things out ; ) I can be rather stubborn.

I'll keep you guys updated if your interested.

[Captain Midnight TT Gold Member]

Any progress?

[Aaron_Silidker TT Addict]

BillDozer said:

Right on. I figured out the fuel pump. Im going to use a 2008 Suzuki LTR pump. It sits outside of the tank like an inline Walbro but it has a built in return system on it. Its a dead head setup at the injector but theres a flow regulator built right into the pump. The LTR throttle body should work nicely aswell.

Again, thanks guys for all your info. HT, I wasnt trying to give you shit, it just sometimes takes me a while to figure things out ; ) I can be rather stubborn.

I'll keep you guys updated if your interested.

BillDozer, I am 99% sure that pump is not regulated and needs an external regulator.

[smcdonn TT Gold Member]

Aaron_Silidker said:

BillDozer, I am 99% sure that pump is not regulated and needs an external regulator.

I think it is regulated, I mean it has a return line..

[msiddalingaiah TT Silver Member]

smcdonn said:

I think it is regulated, I mean it has a return line..

Does the 2008 Suzuki LTR fuel rail have a return line? What's the flow rate of the injector??

[lovin2wheels TT Member]

Is there any kind of kit to convert an older bike to EFI (92 KDX 250)
Is the cost worth it?
What is the biggest plus to EFI over a carb?

[HeadTrauma Get Help Now]

lovin2wheels said:

1.) Is there any kind of kit to convert an older bike to EFI (92 KDX 250)
2.) Is the cost worth it?
3.) What is the biggest plus to EFI over a carb?

1.) No. You'll have a hard time finding a conversion kit for anything but the most popular OHVs.
2.) That depends on what you want.
3.) More accurate fuel control, altitude- and temperature-based mixture compensation, resistance to flooding, fuel cut rev limiting, easy starting, lower emissions, better fuel economy. If you want to use the EFI controller for ignition too, add load- and temperature-based spark control and spark cut rev limiting.

[lovin2wheels TT Member]

Are there any fuel injected 2 strokes out there?

[gravelfreak TT Silver Member]

lovin2wheels said:

Are there any fuel injected 2 strokes out there?

Yes, but only 50cc

But I'm pretty sure HM Honda will come up with a fuel injected CR125 soon. That will probably be the first serious fuel injected 2t dirt bike. That is because in Europe at age of 16 you can drive a bike with maximum displacement of 125cc on the road.

e: oh I forgot to mention that there are plenty of DIY conversions, but I'm not aware of any dirt bikes though

[HeadTrauma Get Help Now]

gravelfreak said:

Yes, but only 50cc

Direct injection has been used on marine two stroke engines well over 50cc for years now.

[Aaron_Silidker TT Addict]

smcdonn said:

I think it is regulated, I mean it has a return line..

You may be right, but the consensus on ATV forums when I was considering using one for my EFI conversion was that the FPR is on the tank and not in the pump.  That is why I switched to a TRX680 pump.  External and totally self contained.

[gravelfreak TT Silver Member]

HeadTrauma said:

Direct injection has been used on marine two stroke engines well over 50cc for years now.

I know, and sleds and many many other engines, but not bikes.

[brianwol TT Newbie]

'09 kx450f has fuel injection with no battery

[HeadTrauma Get Help Now]

gravelfreak said:

I know, and sleds and many many other engines, but not bikes.

I was merely correcting a technicality.

[msiddalingaiah TT Silver Member]

Here's a DIY EFI project for a two stroke Yamaha RZ250:

http://www.smcomp.co...-EFI/index.html

I struggled with the fuel system design on my DR350S FI conversion. I finally settled on an electronic dead head system that's used on some cars (Ford Focus, several trucks etc.)



The AVR microcontroller measures fuel pressure at the rail and adjusts pump voltage to match a set pressure point (about 43 PSI in my case). I'm using a Bosch fuel rail pressure sensor. The system works quite well and requires maybe 2.5 Amps max. The pump is not powered when fuel is not flowing. I'm in the middle of final assembly (slow going as I'm busy with work these days).

[drillergeek TT Newbie]

Can someone please point me in a good direction to research throttle bodies.  Do I need to find something with similar dimensions to the current carb?  I am wanting to play around with this on a spare klr600.  Thanks much!