ZDZ 40 RE, 60 plus oz of fuel now

[vicenterc at comcast.net]

Jim:

Very nice report.  Any comments on noise levels will be welcome? 

Thanks,

Vince 

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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 be en 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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