YS120AC not running

[Ed Miller]

Re: YS 61 Long Stroke "need more help"Since it only takes fuel and air to fire the engine and obviously air is present, fuel must not be entering the engine. Check the needle valve assembly, there maybe an obstruction in the needle socket or fuel nipple. There could be dirt in the needle socket hole in the carb casting. Also, the throttle valve has a groove in it that meters fuel, ensure that it is clean. Be sure the throttle valve is actually opening, it is not uncommon for the throttle arm screw to loosen and even though the throttle arm is moving with the throttle servo, the throttle valve isn't. Is it possible you did not get the disc valve properly engaged on the end of the crank pin making the disc valve out of time ??? I've seen this prevent an engine from running. Let us know your findings.
Ed M.
  ----- Original Message ----- 
  From: Xavier Mouraux 
  To: discussion at nsrca.org 
  Sent: Wednesday, October 29, 2003 11:17 PM
  Subject: YS120AC not running


  Hello guys,

  I have a problem with my 120AC and I didn't found the solution in old messages from the list so I need help.

  I have been flying that engine for almost 3 years now, first in a Nova and this year in a Hydeout. It has been reliable for 2 1/2 years. Then, the day before the Oakville contest, it lost power and RPM (down to 6500 from 8300 on a 15x12 on 30%). Checking the engine didn't show anything obvious. However, we changed all the seals and O-ring, repolish the back plate (small mark on it) and rotary valve, clean the valves, clean the carburetor, check the piston and lining, etc. We didn't remove the cam but could see that it looks in good shape. After reassembly,  the engine runs better than ever (8500 with the 15x12 and 30%). It run fine for 2 months and about 50 flights with regular valve checking.

  A few weeks ago, it begin being difficult to start and wasn't getting normal RPM after a minute of running on the ground during range check. There was smoke on the exhaust that looks as usual. Checking the engine from the outside again didn't show anything obvious but it didn't even start anymore. I opened it last week and clean the valves (some carbon on it), repolish the backplate (a little mark on it). It still doesn't start. New plug was tried, different glow drivers, turn the plane upside down, remove the needle valve, check the pressure (seems normal - a few turn of the prop by hand get pressure in the system), compression seems good. I haven't disassemble the air chamber but will do it tomorrow night. Maybe I will dismantle the carb also.

  What else could I check or try ?

  I would like to fly it a few more time before the snow arrive here in a few weeks :-) 

  Thanks in advanced

  Xavier
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.f3a.us/pipermail/nsrca-discussion/attachments/20031030/95aa51b2/attachment.html