Fuel Injected Lawn Mower Engine...

[BigBrother at MAIL.UTEXAS.EDU]

Bill,

Yeah, I bet that alternator heats up pretty quick sinking 3500+ watts.

> I have successfully run the ignition from a magnetic TDC reference sensor.

Hmm. That TDC sensor is still firing the ignition twice per complete
cycle.  The crank, therefore the flywheel, is spinning twice as fast
as the cam so this means the spark plug is being fired right before
top dead center (compression stroke) and right before top dead center
(exhaust stroke). Oh well I guess there's nothing wrong with that..

Are you running the ignition from a microcontroller that measures the
TDC frequency and advances/retards timing against some kind of load
reference?  I'm still working on that. My initial setup is only going
to have a bastard guess for load... Throttle Postion + RPM!  Later,
I'll upgrade to a Barrometeric Pressure sensor.  Upgrading to MAF
is not really needed. Plus to do it you need to block off 7/8 of
a meter with something and recalibrate it!

> Anyway, exactly what injector have you found that is small enough to work
> on these small displacement engines.

I have not found an injector that would be properly matched to the small
engine, but I'm going to use a stock injector from a 5L Mustang.  Not
because its best suited to the engine, because I can get them free!
However, I will try to get away with running it at 30 - 35 psi.  I still
need to conduct some tests and find out just how short of a pulse I
can get out of the injector.  I have a feeling it will be short enough.
Anyway, we can get away with running pretty rich at idle, although I'm
sure there is a limit before it effects throttle response.

Another thing you need to consider is a fuel pump and pressure regulator.
For this application, we really could use a small fuel pump, but I don't
know of a small pump!  I'll be using a (major overkill) 88 L/hr
Mustang fuel pump mounted into a good old 1 gallon gas can.  Yeah, it will
cycle the entire can every 3 minutes, but again, its free.
It looks like I will have to break down and buy an adjustable pressure
regulator (or take the one off my car).  We absolutely have to adjust
the pressure down for the little engine.  Of course, if I can get
a real short pulse out of the injector, then a stock regulator will do.

I'm not sure how far other people are going to go with the fuel
injected Briggs & Stratons, etc. I'm just messing with them so
I get a grip on fuel injection: microcontrollers, sensors, and
actuators before I go on to something more important- like a
car engine, etc.