OS 91 HZ-R needle settings

[mgjackson]

Hi,

I've asked a similar question about the OS55 on my Trex 600 before, and now I need to ask the same for the OS 91 HZ-R on a Trex700 DFC.

And for pretty much the same reasons - I've been trying to tune up the engine and now I've mucked it up and I need to start again...

What's a good starting point for the needle settings?

When I asked before for the OS55 I was told 1 and a quarter for high, 1 and a third turns Mid which I only had to tweak a couple of clicks to get it perfect.

Thanks,
Matthew

[matjonze]

On a standard align pipe and 2 gallons of 20% running, i'm down to 3/4 on the mid and 1 1/4 on the high with factory idle. Still doesn't sound right or pull right and bottom plate still fairly cold. I feel theres a lot more in this engine yet.

[enterpryse]

On a standard align pipe and 2 gallons of 20% running, i'm down to 3/4 on the mid and 1 1/4 on the high with factory idle. Still doesn't sound right or pull right and bottom plate still fairly cold. I feel theres a lot more in this engine yet.

About the same set up as mine (on Optifuel 20%). Although mine runs fine I know it's a little rich.

[Rotorhead]

Is it a pumped version?

If it is you will actually have to go even leaner to get the performance, pumps tend to make motors run richer due to being force fed fuel.

I have the HZ, not the R on my 700, but the principle is the same, I ended up with the main needle at 1.25 turns and the mid at just a couple of clicks under half, and it still is a bit rich.

Once you've got your high speed needle set the best thing to do for the mid is to do some fast climb outs, at least 50ft, and then when you come off the collective, at the top when it stops you need to lean out the mid so that you don't get a massive cloud of smoke, a small increase is fine, but not massive, keep doing this until its running consistently.

Watch these vids..... Nitro Engine Tuning 101 - HeliFreak

[enterpryse]

Is it a pumped version?

If it is you will actually have to go even leaner to get the performance, pumps tend to make motors run richer due to being force fed fuel.

Yes mine is pumped.

[dw45]

Good place to start is where OS recommend in there manual. Top(high end) 2.5 turns from closed, Mid: 1 turn from closed and idle at the middle position. then tune as for three needle carb high end first. a few videos and write ups are online.

[dw45]

Here is a good write up on engine tuning. http://www.jupiter-venlo.nl/Algemeen...0EN%20v3.1.pdf

[mgjackson]

Good place to start is where OS recommend in there manual. Top(high end) 2.5 turns from closed, Mid: 1 turn from closed and idle at the middle position. then tune as for three needle carb high end first. a few videos and write ups are online.

That's what I was hoping to avoid because after fiddling there's a good chance I'll end up with it all borked again. Reading above, 1.25 High, 0.5->0.75 mid is a good place to begin.

Really need to watch all the videos tho! :-)

[mgjackson]

Here is a good write up on engine tuning. http://www.jupiter-venlo.nl/Algemeen...0EN%20v3.1.pdf

Interesting quote:

Shimming the engine
The OS91SZ engine is tuned for 15% Nitro when shipped.
If you want to use more Nitro then you should install one of the extra
shims that come with the engine (0.008 inch).
The shim enlarges the distance between the piston and the cylindered.
This will delay the detonation to compensate for the higher Nitro
percentage.
If you do not use the extra shim the engine will not run smooth and you will get symptoms like if
you are using a glowplug which is too hot. But no plug is available which is cold enough to
compensate the pre-ignition. You have to use the extra shim.

[matjonze]

That would be in reference to using 30% vs 15%, opti 20% should be fine with the standard shim.

What rotorhead states follows mine line of thought, I can lean out the mid a little more as thats where it seems to be rich at the moment.