ZDZ 40 RE, 60 plus oz of fuel now

[Jim_Woodward at beaerospace.com]

Hi All,

Here is an update to the ZDZ 40 RE bench running.  Since first post, I 
received a number of private emails expressing some interest and 
excitement in the topic.  Setup:  ZDZ 40 RE (purchased Nov 04, Falcon 
ignition, Walbro carb), Webra MACS header, Mintor 140 AL pipe, 93 Octane 
with Lawn-Boy Ashless oil mixed 32:1 per instructions.  The only 
modifications I've made thus far have been to add a longer throttle arm to 
the carb. 

After running 60 plus oz of fuel through the engine, you can imagine I've 
played with the needles a little bit.  Every 1/4 tank or so I noticed 
small changes in the sound of transition, idle, or top end, so I would 
correspondingly change one of the needles slightly.  The trend of the 
motor was that the more the motor broke-in, the richer it seemed to run. 
Small changes on the needles are quite effective.   What I found was that 
if you have the idle screw too lean, the engine will run fantastic 
(perfect), but the engine will take 30 flips to start when cold.  If you 
have the idle screw in the right location, cold starts (including 
priming), 10-15 flip range.   On the bench, flipping with choke on and 
full throttle (ignition off of course), is not practical as I've left the 
throttle barrel return-to-idle-spring engaged for bench safety.  Utilizing 
full throttle, choke on, while priming is a procedure I've been told 
quickens the starting of the engine.  Again, have not tried as I do not 
have a servo controlling the throttle on the bench.  Even at low-throttle, 
choke closed 5- flips, the rest is done at low-throttle, choke open, 
ignition on, until running.  Even without the most advantageous bench 
starting procedure, the motor cold starts pretty quick.  Hot starts have 
been "first-flip" starts 98% of the time.  I'm happy about this as it was 
a concern of mine.  I am looking though to reduce the "cold" start time a 
bit.  If you consider 2 seconds per flip, I'm looking at cold starts in 
the 30 second range. 

Initial running through 50 ozs:  Idle was smooth, but high through about 
50 oz.  The one time my tach worked, it read around 2500 rpms (dead 
batteries).  I was beginning to wonder if the throttle barrel did not 
allow enough "throw" to close the barrel and reduce idle rpm.  Right about 
the 60 oz mark, the idle seemed to drop dramatically.  I ran for a few 
minutes like this, then stopped the motor.  After a total heat sink to 
ambient temperature, I started it again and the idle hit this low-idle 
mark again and has since, which leads me to Note One:

Note 1:  Do not take motor off the bench until ridiculously low idle is 
reached.  You will know you've reached this point, because the windmilling 
of the prop and small mechanical noises of the engine make more sound 
(mild sound) than the "popping" of the combustion cycle. 

Note 2:  Don't worry too much about the low-end needle.  Leave at 1.5 
turns (factory suggestion) until Note one is reached.  Once the idle 
drops, adjust it for cleaner running.  Mine, even barely ticking over, 
still has very little vibration.  Feel free to adjust the top-end needle 
slightly until you at least have clean 2-cycle full throttle reached.  At 
the 1.5 top-end needle starting point, the top-end is VERY rich.

Note 3:  I've broken in this engine with a 18x10 APC Imac prop.  I've done 
so because the larger props have not arrived and I was anxious to get it 
running.  Thus, I'm not sure what effect a larger prop would have done to 
the break-in procedure or specifically the high/low idle point I've 
mentioned above.  Given my current information, I don't feel mounting this 
to a plane for first flip is a good idea.  Put it on a bench, get to know 
the starting procedure, etc.  However, with the smaller prop, the engine 
does seem to really sing with rpm.  So, I have no doubt that this 
particular engine is not rpm limited or such.  I can hardly wait to get 
the larger props on it.  I was resistant to bench running, but alas, it 
was great advice and I'm glad I took it. 

I also called two folks who monitor the list to 'listen' to the engine 
while it was running, just for fun.

Enjoy the hobby,
Jim W.

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