Maidened my CA 27% the other day. (first flight was VERY scary due to a way aft CG, and some aileron flutter!)
I'm usuing a slightly used ZDZ50 NG (almost done breaking in)
Anyhow in the 2 flights the midrange seemed very burbliy, a few quick sputters in the midrange 1/4-1/2 thottle.
Downlines, if I throttle back the rpm would stay up, (but that seems like a normal engine thing to happen). Engine runs well on the ground, and when I gun the throttle, always is very responsive, no lag or sag. Uplines, the engine doesn't gain or lose any RPM, so I figure I have it set about right.

High end tached at 6900 RPM on a MenzS 22x8
My Idle seems high... 2800RPM


I'm thinking that the LOW END is RICH? Figured I'd ask all the pros before I start accidentally turning needles the wrong way...
Thanks!
~Andrew

deleted- I assumed information wrong

You must have an in cowl muffler -of some type -
don't worry about rich sound in mid range - it means nothing .
good throttle response is everything
set idle screw IN till the engine sags -then oen a tad - try to rev it - open needle a bit if it tries to kill.
it is a trial and error adjustment -but if all is OK with carb, the low needle will be about a turn and a 1/2 or so open from seated.
The engine really likes big can mufflers or tuned setups and will run that prop way up into the 7000 range on a pipe .
As mentioned -- DO play with the needles -turn em -listen run up the engine listen again-
Only you can be the expert on your engine - and it ain't hard to learn -just do like your school teachers commanded - LISTEN!

.

I'll lean out the low end needle.... The midrange weird sound, is definatly not ok, its more like strange dropouts, and definatly is NOT a relable engine sound I'll keep turning the low end in as far as I can get it, and have it run reliable on the ground... and then put her up in the air and see what happens...
I was playing with the needles, just had is nice on the ground, but it's sounding different up in the big blue.
I'm using a in cowl supersonic muffler.

right now I have the high end out at 1.5 turns, and the low out 1.25...

Carb can close all the way, but 2800 was as low as I could get it reliably, I bet if its leaner, that'll help.
Whats a normal idle for a ZDZ50?

Thanks for the replies!

Deleted Mis-read response. Thought you said 2800 with carb completely closed.

Was running rich on the low end.... It hesitates a bit on the ground when I gun the throttle from idle, but runs perfect in the air. weird....

Anyhow I'm happy, no more 4-stroking in the midrange.

~Andrew

You are set a bit lean on the bottom end --and th hesitation on the ground is just due to the engine hqaving to work harder sitting there -as opposed to moving forward thru th air.
But- you are pretty close -as long as there are no gasps upon adding throttle -in the air
now slightly enrichen high speed needle - jut a tweak -until the engine does not hit max revs unless climbing .
If you adjust any two stroke aircooled engine for max level speed -it will be too lean for max power on uplines - ANY brand .

Take a short trip over to the RCS website. Take a look at the instructions they provide to everyone regarding tuning the carb on a gas engine. It applies to ALL gas engines using a Walbro, Tillotson, or Zama carb.

It's just too darn easy to do, and a tach is not needed. If you're not deaf already from glow engines, tuning the engine by ear is a simple affair. Peak the high needle, back off a tad. Drop the rpm to a little less than half and peak the low needle. Go back and re-peak the high needle, again backing off about 100 to 200 rpm. Return to the lower power setting and peak the low needle. Leave it peaked, don't back it off. You may need to touch the high needle once more, but all the adjustments will likely be in the 1/16 of a turn area.

yes -all good
Unless you get the engine very hot during an extended session of lean running.
The proper adjustment technique assumes the engine is running in acceptable temperature limits.

I read the stuff on RC showcase... Thats why I thought it was rich on the low end.. so I leaned it out today, and the burble 4 stroke sounds in the midrange went away... on the ground it heisitates ocationally if I Really gun it, but doesn't die... Seems to run fine in the air now. I just didn't want it 4stroking in the midrange like it was the other day.


~Andrew

Hi Andrew, I don't mean to be critical, or make judgements. I have to ask why the CG was so far aft, especially on a maiden flight? My question is posed NOT to blast you... but hopefully some will read this and be more careful about the CG location on a new plane. I have only been in this crazy hobby 5 years and have had about 12 planes. (5 are still with me.... some I sold, and the rest........ well, you know!) I always start at the "close to forward" CG location for my first flights and have never experienced a bad first flight. ..... lownslo

Well, the CG wasn't that aft (from what I thought) it was about 1/4" behind the wing tube. It definatly flew like a way aft CG though! And the Instructions for the Columbo Anderson are (VERY) limited, and don't offer any hints as far as balancing.
It's all good now, everything is locktite'd and the CG is sitting very nice right now. Just the 1st flight was a wee bit scary.

Just a thought, but some of the auto advance ignitions will have a small "burble" in the mid range that you can't get rid of. It's just the nature of an ignition that suddenly jumps to full advance at 3 or 4K rpm.