Engine tuning on OS91sx

[ShinOBIWAN]

Hey guys,

I bought a little used OS91sx-h non pumped off ebay and after sticking it in the heli I'm having some issues with it.

I've got very little clue about tuning and I was told by seller that this would be in the ballpark and would just need a few click for the muffler since it was already tuned. The motor looks mint and its apparently only had about 8 gallons through it.

However, its eating fuel pretty badly and the skids and side of the heli are covered in nitro. I think by the looks of it, its burning 3/4 and throwing the other quarter straight out or something. Seems to have OK power.

Where do I start and what is a healthy amount of nitro to be coming, can you have none at all and still run safe?

[DavidH]

What fuel, what muffler, what glow plug, what gear ratio?

As for the seller in would be in the ballpark as for tuned. That would only be if your using the same fuel, same muffler, same gear ratio, and flying the model in the same location as he was.

David

[ClayK]

Shims?

[ShinOBIWAN]

Hi the setup:

OS 91 SX-H C-Spec
OS no 8 Plug
Coolpower Heli 30%
Thunder Tiger 90 size muffler for OS
No Shim

Location is UK so average temps from around 12-25c degrees.

Thanks for any help

[ClayK]

Current needle settings? (assuming it's the stock carb)

What helicopter is it in (for gear ratio)?

[ShinOBIWAN]

Current needle settings? (assuming it's the stock carb)

What helicopter is it in (for gear ratio)?

Hi Clay

Its stock carb with idle needle centre, high needle is approx 2 turns from closed, mid needle is approx 1 turn from closed.

Gear ratio is 11t pinion and 93t main gear so approx 8.45.

Engine run extremely cool when touching the backplate after running it for about a minute.

[DavidH]

Too rich on the main needle. 1.5 turns open from fully closed should be close.
There should be one .008 shim under the head. This shim is stock on the motor. As for the Cool Power 30%. Unless you have a good supply of it, it is going to be scarce to find. Morgan has not made any fuel higher than 20% nitro for several weeks now. I don't know when they will produce anything higher than 20% again.

David

[Lota Fun R]

The "cateye mod" is a must, it is very hard to tune/impossible stock.

I bought the 60k control valve which is pretty much the same as doing the cateye mod.

All the needs to be done is to file the cateye slot a little bigger, looking at it you can see where it isn't even on each side.

Having done the 60k mod, I run the main at 3/4 turn out on start up and then the carb smart adjusts it to about 1 to 1&1/8th turn out, which is perfect.

No shims, just a gasket.
30% cool power
adjust low needle so when you pinch off the line while idling it take about 4 seconds to start dying. do this after it warms up.

1850 & 1950 headspeed respectively.

[DavidH]

He has a 91 SX-H CSpec. The Cspec comes stock with the 60K carb.

The 91SX-H is the one that had the 60 L carb and needed some mods to it.

David

[Lota Fun R]

He has a 91 SX-H CSpec. The Cspec comes stock with the 60K carb.

The 91SX-H is the one that had the 60 L carb and needed some mods to it.

David

I have the C spec also, the control valve I bought for it is different, as in, it's already been fixed, they opened up the cat eye from the factory. I can visually see the difference.