intro

[Sam Stoney]

I've been lurking here for a few days and what I've seen (except for the
spelling incident) is enough to get me interested in the EFI project I just
shelved again.

I have a Ducati 750 V-twin motorcycle that I adapted a TEC 2 system to. From
the get-go I've had several problems. The first is lack of any test
facility. Being a race bike I can't test on the street and I prefer to spend
my time at the race track racing.  I'm addressing this problem this year by
setting up a complete secondary fuel and ignition system. This way I can
test during practice and go over to the proven system at race time. But I
digress; this isn't of use to this group.

The -technical- problems I have seem to be related to my using a MAP based
system on an odd-fire v twin with radical cam timing. Needless to say I've
got a -very- uneven manifold pressure. One solution I've been considering is
going over to a MAF input. Specifically I was going to combine the two
intakes into a chamber and then put the MAF sensor on the end of that. The
throttles and injectors would remain right at the intake.

Having this additional volume would dampen the airflow going through the MAF
sensor. Of course, it would also slow down the response of the overall
system to engine demand changes. But I figure I can compensate with throttle
position based enrichment. 

I guess I'm trying to decide whether I should go to the trouble of doing
this or simply continue to try to make this system work. Any suggestions,
general or specific, would be welcome. It has already been suggested that I
throw away the bike and get a car or at least a 4-cylinder engine to play
with but I'm stubborn.

On another topic - at one point in this project I took a Seimens injector
(new) and  mounted it on a throttle body mounted to a clear tube. I then
attached the tube to a vacuum cleaner and attached a 40PSI clean water
source to the injector. Using this apparatus I could then watch the way the
injector atomized. I tried this with several different sized injectors,
different pressures, and a couple of used Bosch injectors. In every case the
injector emitted an incredibly squirt-gun like stream much to my suprise. I
guess I expected it to look like those posters I see in garages showing
cleam vs. dirty injectors. Perhaps the very different viscosity of water
made a difference. I would have used gas but when the vapor got to vacuum
cleaner.....:-0

The injector was pointed roughly 60 degrees down the intake. When the stream
hit the other side it atomized rather well, so it didn't really matter that
it was a stream. The atomization was consistant through all throttle positions. 

At one point I cycled the injector with the throttle WO and the vacuum off.
The vacuum generated by the injector's pulse alone was very substantial.
This -must- have a benificial effect on performance. Higher pressure
definitly increased this vacuum too.

I also tried the same experiment with like sized carbs attached where the
throttle body was attached. An older Mikuni design seemed to atomize
slightly better; a brand new Keihin flat slide (arguably the best carburetor
currently available for racing) gave a substantally finer atomization right
up to full throttle. 

But the carbs didn't flow very well when I shut the vacuum off.:-)

Has anybody out there measured the pressure differential in a port before
and after the injector to quantify the effect the injector output has on flow?