OS91SZ-PS Tuning

[slammers]

I have an OS 91SZ pumped in my Synergy running 1950 head speed. I am not using muffler pressure and I do not have a one way valve on the vent line.

I can not get it to run quite right. The needle settings do not seem correct so I was hoping others can let me know where their settings are.

With the suggested settings this engine was completely rich. I kept turning everything in until I could get the head speed to come up. I am now completely closed on the midrange and less than 1/2 turn on the high end.

With these settings it is still very rich in the mid range. During full power climb outs it sounds ok. Less smoke than at hover but there is excess smoke there.

I have not touched the idle setting. I was going to lean it out to see if that affected the midrange but when I do an auto it tends to take a while to idle down so it sounds like I may be a little lean in the low end.

Do these settings seem right? At 1/2 turn on the high end I am afraid to go any leaner. I do notice that the regulator drips fuel around the black portion of its body. The two screws holding it together are tight so I do not know why this is leaking.

Shawn

[Aviation addict]

Shawn,

I've not had my OS SZ pumped very long, but have leaned the Idle / Closed the Mid totally / and have the High at about 1 turn - although I have taken it to 3/4's in the past - with no signs of lean running. Having the SZ's mid needle fully closed seems quite common. I just bottled it with the high needle at around the 3/4's point as I don't want to harm the engine and don't have the experience to tell when its bordering on lean.

I'm also seeing leakage from the Regulator's seal (I think) - with the bolts tight. I'd like to know what effect that might have on the engine's performance ....

My idle seems right but does tend to hang a little during an auto. It comes straight down though if I click into hold during a max pitch/power climbout which I understand is a sign that the idle is good.

I'm running with no muffler pressure and no check valve just like you by the way.

[sookainian]

guys i notice u all are not running any valve. Then when u go inverted, how u prevent the fuel from coming out ?

[slammers]

While running there is always fuel flowing out of the tank so air must be sucked in to the vent line. This negative pressure prevents fuel from leaking out the vent. The valve is only required to stop fuel from leaking out when the engine is not running..

Shawn

[sookainian]

cool, i didnt thought about that. Hmm ok i got a Stratus, just wondering, how u guys seal tight the nipple on the tank ?

Coz i notice sometimes there is slight fuel coming out from that part :arggg:

[HiroboFreak]

Sorry to bump an old thread guys but I'm having the same trouble with my pumped SZ in my Synergy. (No muffler pressure, no check valve)

It's only done 2 tanks so it's still running in & still tight I assume.

I'm assuming it's rich as I can't get the headspeed over 1870 (running a flatline 100% curve with a RevMax)

I've taken the main down to 3/4 turn, the mid is closed & idle is at factory setting.
I'm a bit worried to close the main needle any further.
Checking the crankcase temp on the side, low down as close as I can to the backplate, temp is about 45-50C(113-122F)

Is this temp still ok? It's my first 90 so I'm not very educated with them.

Should I go leaner & see what happens??

Is it common to be under 3/4 on the main needle?

Thanks in advance.

Regards,
Dennis.

[sookainian]

I think it's normal for 3/4 turn. Mine is around there too. But not really getting the power and i just dont know which part of the engine is leaking badly . .

Always after a flight, my base plate will be soak in oil :bomb:

[HiroboFreak]

Yeah like I said I can't even get the desired headspeed in a hover.

Do you have any idea of the max acceptable temp?

That'll be a good guide.

[sookainian]

below 100degree to be safe :mrgreen: haha not very sure...

[SteveL]

I will run them in the 180f area.
Heck it is almost as warm as yours is on a summer day.
What Nitro Fuel are you running?
Any pining when you come off a full power manuever?
Keep running that needle in till you get her a little lean then back her out.
I have heard of people running them with the mid closed and the high @ 3/8.
Mine has a cline so the nubers will not help you.

[HiroboFreak]

Hi Steve,

I'm running 20% nitro.

I'm not sure how accurate that temp is so I'll be checking the temp at the head in future. (200-210F on the head) that's about 93-98C.
If I keep it under 95C I'll be happy.

As for pinging & full power manouevers.... this is a brand new machine, (and engine) only done 2 tanks so I'm not loading it yet.

I just wanted to run it in at the headspeed that I intend to use, just richer.

Do you mean guys are running 3/8 turn open on the main?? :shock:

I've got a fair way to go then. I was concerned that 3/4 turn seemed very thin but if guys are running 3/8 then that makes me feel better. :)

I'll keep things gentle until I've put about 5 tanks through her, then start dialing it in.

Thanks very much for your help guys.