Hi all,
Here is my latest problem with my DZ 170 glow: WOT with APC 19x11 is no more than 5400 RPM. Idle is 1700. Acceleration smooth.
The engine ran at WOT giving 7200, until one day it got stuck at 5400 no matter what I did trying to remedy it: One change at a time.
Replacements:
- Piston Ring Sleeve
- Head assembly
- Head gasket
- Bearings
- Pump Diaphragm
- Glow plug
- Carburetor insulator
Actions:
- Polishing cam followers
- Verifying valve lash, cold and hot
- Verifying valve timing
- Making sure the crank pin sits in the correct groove of the disc valve of the back plate
- Making sure there are no leaks
- Fuel consists of 20% Morgan LS oil, 30% Nitro, 50% methanol
- YS mount intact
- HS needle 1 turn open
Any idea on how to fix the problem will be appreciated.
Thanks!

From what you've already checked, the engine should be OK. Make sure the throttle barrel is opening fully.

How time flys?
That DZ170 CDI of mine was running great until one day (early 2023) it started coughing and misfiring again. Did a few quick checks and a few more flights but nothing improved and then noticed the intake valve spring felt "soft" and discovered it was broken right at the bottom. Replaced it and it made no difference. There was noticeable wear in the fuel pump bore with a small lip at the bottom of the piston stroke which I thought could have been causing the pump piston to hang up under certain conditions and stop the intake valve from fully closing but I put a new pump on it and again, no change. I messed around with a few things but I was totally sick and tired of chasing problems and I was enjoying flying helicopters with an OS 105HZ-R that's never missed a beat so I stopped flying it.

Fast forward to early 2025, and I decided to replace the throttle body on the brand new DZ200CDI I had that had never worked properly from new and Hey Presto!!, I had an engine that I could put in my Aries 07 and go flying with again. The 200CDI isn't as "nice" in the Aries as the 170CDI but for sport flying I'll take a running YS over a non-running YS any day of the week. Did I mention the third set of servo's I put in in 2022 (nice Futaba HV ones) the pot of one aileron servo has a worn spot at neutral in it already from the vibration. I swear if I ever replace them I'll mix in flapperons just to keep the ailerons away from neutral more often to reduce that spot wear.

So I guess it's safe to say after 15+ years of flying with two YS engines that my sum knowledge of them boils down to "if it's not running right there's something wrong with it" and your guess of what that is, is as good as mine . But , please let us know what you find if you figure it out.....

Hey Brett,
Glad you got a YS running so you can fly a fixed wing aircraft! ;-). How do you like the Aries? I have a kit that I’ll get around to building someday.
i’ve Run glow engines since 1967, but 3 years ago I finally took the plunge and started flying e-power. Actually I blew out my right knee and e-power was my only option for regular flying. I started with a Naruke Asuyler ARF which I originally intended to power with a YS FZ 70, but I was able to set it up for electric. I confess I love e-power for pattern, for all the reasons I had heard about. I still enjoy glow power, especially in older pattern designs. The largest YS 4-stroke I now own is the 115; much simpler than the big DZs.
Happy flying!
regards,
Will

Hi Will,
I'd regard the Aries 07 as a "nice" plane to fly. It's (mine's) not mix free.
It also tends to have a habit of going off line quickly in a manoeuvre if you start out a bit offline.

From an F3A perspective it's about 3 generations out of date and you're going to struggle with any maneuverer that requires high G levels of knife-edge performance. It's snap roll performance has never been crisp either.
I tend to just sport fly it now, which for me is mainly the pattern schedules of the era without the snap rolls or spins and flown in a bit tighter occasionally throwing in some of the newer knife edge stuff modified to remove the really high G knife edge components.
Just generally convincing those in the pits that it must be less windy up there, than they're feeling on the ground

The DZ200CDI with 21.5x10.5 prop has improved vertical and downline braking compared to the 170CDI but this was an airframe designed around a 17x13 - 18x11 (I was running 19x11) and the bigger prop does make it's presence felt at time..

Hi all again,
Found the culprits.
1. The Insulator gasket of the DZ200 P/N E2192 is also sold under P/N F2192, although these are two different items, as defined in the exploded view of both engines. I was lucky to find in my drawer the correct F2192, which belongs in the DZ170.
2. The Insulator was wrongly installed with the small cell facing the Intake pipe, instead of facing the air entrance into the carburetor.
Now that the correct parts are reinstalled in their correct orientation, RPM is back again to 7,100 with APC 19x11" and Morgan 30%, and 6,800 with Morgan 20/20.
Thank you all for the sympathy, and always check twice!

Thanks for the update.
I just pulled the back off mine for a look, and to check how my storage method is going corrosion wise. You might just tempt me to get mine going properly again too.