Trex 700 - OS 91 HZ PROBLEM

[Daniele76]

I carburetion problems with my OS HZ with pump without pump.
This is the problem when they are idling and first heli that rises from the ground the engine pulls tears, it seems that emaciated alone. I turned the lever of the minimum clockwise 1 / 4 compared to the neutral position, but nothing to do, it seems that is fine but then when he lands emaciated by itself and the clutch engages to tears.
Fuel use to 20% nitro and 23% kl198, the pin of the maximum is 1,5 turns and the middle 1,5 turns.
As gasket thickness under head or engine you have?
I have two for a total of 4 dec.
What aid? :arggg:

thanks guys!

[OTA]

Didnt understand much of what you try to explain:thinking.
But in regards to the head shim the 0.2mm shim is enough for 30% Nitro. 0.15mm is for 15% Nitro.

[Mercuriell]

Didnt understand much of what you try to explain:thinking.


That's the problem with online translators ! = anyway I think your mid range needle is a bit rich suggest bring that in to 3/4 turn - main needle at 1 1/2 turns shoud be fine to start with - also clean out the needle valve - just remove it completely (main) while connected to fuel and let the fuel wash out any debris

[Shockwave 3K]

Will you get lower performance without the shim?

[OTA]

So, you did understand and read it as too rich (the "tears") !?:)
Sorry for not understanding the issue fully.:o

First of all: Change the shim to only one 0.2mm.

PS ! While the recommendings by Mercuriell might seem reasonable, be warned about that might be way too lean, but thats dependant of your climate. Take it leaner step-by-step and listen to engine, check smoke trail and temperature very often while you adjust.

I am on 1,5 turns (+- a click or two) each here in Norway and typical spring temps (10-15deg). If i went to 3/4 on medium, it would be bye-bye to that engine:(.
Be also aware that the medium needle is a very important range for the heli engine as the engine runs in this region quite a lot.

One good thing about the HZ engine: While it seems to be more power when going lean, its not true (its only slightly more rpm and seems more responsible around hover). However, it will bog down very easy. The engine just likes to run slightly on the rich side

[LoveMyTrex]

my mid needle is still 2 turns out. have never really bothered to tune it as I am always on the power and in the high needle. slightly rich as in what temp?

[Ludde]

I also run the HZ-PS without the pump, im on 1 3/4 turns on both needles.. was down to 1 and 1/2 but it loost lots of power so I had to open the middle needle slight more..

[Mercuriell]

Good points from Scandinavia - I forget sometimes not everyone in 30°C climes - as the temperature goes down the needle needs to be opened out more as there is more oxygen to burn the fuel - wrt the middle range must confess I've never spent too much time tweaking this - I think I recall Bobby Watts mentioning he flew with it closed

[Tom Burgess]

I think I recall Bobby Watts mentioning he flew with it closed

Quite a few people heard this too and toasted their motor's :shock:

[John Cook]

I think from my take on the OS needles is that alot of people have the idea of what the needles do wrong!

The main needle is not a "high" needle. It's the main needle for the majority of the carb's range.

The shorter needle is not the "mid" needle, it's a transition needle that helps to richen or lean the middle area yeah, but it's there for tuning the transition between the middle and higher end of the carb. A larger bore carb can have a harder time coping with mixtures without that needle.

Further, on a YS the "mid" needle controls the majority of the carb range and fuel mixture whereas on the OS the "high" or main needle controls the majority of the mixture.

Get your transition needle set to where the carb transitions well throughout the range and leave it. Fiddle with the Main needle for your overall tune. My 2 cents on the OS, from my limited time farting with them :).

YS is almost opposite to tune and I believe why alot of people have issues with the YS as they are used to tuning OS motors.

[mami]

hello..
yesterday..ı try to break in...and tune the engine...but engine was burn...
t-rex700...os91 hz
at first..high needle 2 and1/2 turns open from fully close..and medium needle 2 turns open from fully closed...idle screw was naturel(12 o clock)
ı was 3 tank hover at %60 thr power..at..+5 curve
at 4. tank...ı was close high needle 1/2 turn...it was 2 turns open from closed at that time...
then ı hover heli...than ı turn the idle clockwise 5 degre..
at the hover engine stop...and never start..ı was pull out engine...piston was burn....

why..??what was wrong that ı done..

now ı order a new engine os91hz....but ı dont know to do break in and tune the engine..??

[OTA]

Hmmm, your definitions on the needles here is conflicting the OS 91HZ manual:thinking where the needles working range is shown in a chart. There is the medium needle shown to cover the range of 1/3 to 2/3 of the throttle range and the high needle the rest. It is further noted in bold that at full throttle or close to full, neither the idle screw nor the medium needle influence the mixture strength at all.

The engine will be in the 1/3 to 2/3 throttle range more often than we like to believe, and thus pretty important NOT to lean this too much as i have seen some people advice.



I think from my take on the OS needles is that alot of people have the idea of what the needles do wrong!

The main needle is not a "high" needle. It's the main needle for the majority of the carb's range.

The shorter needle is not the "mid" needle, it's a transition needle that helps to richen or lean the middle area yeah, but it's there for tuning the transition between the middle and higher end of the carb. A larger bore carb can have a harder time coping with mixtures without that needle.

[Ludde]

looking at the parts list of the carbs I figured it needs more open needles runnin a PS without the PS=pump, its not the same needle seat, didnt matter for me opening the high neeedle it still was weak but when opening the middle needle to 1 and 3/4 it was back on power.. 1 and 1/2 was real weak on power

also you got the regulator blocking the fuel abit.. not much but a tad..

so its not the same runnin a PS without pump as a HZ without the PS carb parts..

works for me :-)

ohh was running mine at zero to a few degrees abow zero celcius..

the fan on the 700 is like a tornado also..

[John Cook]

Hmmm, your definitions on the needles here is conflicting the OS 91HZ manual:thinking where the needles working range is shown in a chart. There is the medium needle shown to cover the range of 1/3 to 2/3 of the throttle range and the high needle the rest. It is further noted in bold that at full throttle or close to full, neither the idle screw nor the medium needle influence the mixture strength at all.

The engine will be in the 1/3 to 2/3 throttle range more often than we like to believe, and thus pretty important NOT to lean this too much as i have seen some people advice.
well if I'm wrong I apologize. This is how it was explained to me awhile back. That is why I was told some people elected to just do away with the middle needle on the SZ as that carb didn't work as well as the carb on the HZ, and would often have a lean spot in the mid until it was blubbery rich effecting power. The solution at the time was to richen the main and then close the mid. I'd personally be afraid to do that, but that is how it was told to me.

Again, I could very well be wrong. Just ask my wife lol. She'll tell you how often I'm wrong :bomb:

[LoveMyTrex]

hello..
yesterday..ı try to break in...and tune the engine...but engine was burn...
t-rex700...os91 hz
at first..high needle 2 and1/2 turns open from fully close..and medium needle 2 turns open from fully closed...idle screw was naturel(12 o clock)
ı was 3 tank hover at %60 thr power..at..+5 curve
at 4. tank...ı was close high needle 1/2 turn...it was 2 turns open from closed at that time...
then ı hover heli...than ı turn the idle clockwise 5 degre..
at the hover engine stop...and never start..ı was pull out engine...piston was burn....

why..??what was wrong that ı done..

now ı order a new engine os91hz....but ı dont know to do break in and tune the engine..??


you know you don't have to buy a whole new engine right? you can buy individual parts.

I almost ruined my engine by running a tank through it with the fuel clamp closed. evidently my fuel clamps didn't clamp the fuel line all the way and it allowed my engine to run. It was dark out so I could not see that I had very little smoke.

check for that. 2.5 turns out is plenty to break it in.

[solvik]

Today i re-tuned my OS 91 HZ PS.
I ended up with middle needle at 1 1/3 turn and high at almost 1 1/2 turn. The engine runs great.

But my problem is that the enigne is running very hot.
My Multigov says that max temperature is 125-130 C.
Is this safe for the engine ? If i richen the engine it`s to rich to get the headspeed up.
When i tuned my engine i removed the linkage on the servoarm to the needle.

I have to run atleast 122c on multigov carbsmart feature to run the engine.

I use 20% nitro fuel.

And the engine seems to run leaner when fuel is lower. But my headertank is full.

Can there me any problem with my pump ?

Does my temperature seem right ?