Hi everyone,

Some time back, my a/c met with an unfortunate crash.
The result of this crash was some broken cooling fins on the engine, and a some light damage to the muffler.
The High-speed needle (HSN) assembly too suffered some damage, however the engine as such seems to be running fine.

However, one thing that I noticed was that the HSN setting had to be changed completely.
As against the normally recommended setting of approximately 1.5 turns, I needed to open the HSN by only 0.75 turns.
  - Opening the HSN beyond this would result in the engine running too rich.
  - Also the HSN has become very sensitive.

I suspected that the issue might be in the HSN assembly, so last week I replaced it with a completely new one.
However, the problem still persists.

Can anyone help me with this?
Is it okay to run the engine at 0.7 turns, even though its not acting Lean in any case?
Or could this be some other issue?
  - The muffler seems to rotate a bit due to the vibrations and perhaps leaks some (really very little) oil.
    But I thought that this would make this engine lean (due to reduced back-pressure) rather than rich.

Thanks in Anticipation,
aX

There is a big impact on the pipe (muffler) used on the main needle, in my experience. A while ago, I was trying different mufflers on my Trex 600N, and the number of turns on the HSN varied between 0.85 and 1.25 depending on which pipe I was using (Hatori / MP5 / Align).

When it comes to 2 stroke glow engines, just go with the "3-to-5 second back plate temperature" rule of thumb for tuning, and you should be fine regardless of where the main needle is.

consider the following - you said the HSN ASSY suffered
slight damage - it is possible that the threads have gone
out of true and what you think as closed is not actually fully closed.
(I could have worded that better). That would explain the .7 turns - since
you are not able to fully close the needle.

also - are you using the same fuel ?

I think Saikat is on the button here

Saikat da - He said he completely replaced the HSN assembly. That is why the muffler becomes the primary suspect.

hi all,

Thanks for your timely suggestions.
As it turned out, the issue indeed was with the Muffler.
Went to the field, changed the Muffler and now the engine tunes well. Managed 3 flights after that with no dead-sticks.
Thanks also to Jamal & Hemant Sirs for their help in setting up the engine on-field.