OS91SZ Help

[Lzfalcon]

I have been using the thunder tiger engines until I built my 90SE, I decided to put an OS91 SZ not pumped. Yesterday was the maiden voyage. The engine started up no problems. at a little better than half stick the heli went into a hover (heavy thick smoke fom low to mid stick) hearing other helis with the same motor, i did not agree with the sound or head speed. It was in the hover for about a minute when the motor died. I felt the motor and the motor was relatively cool. I started the heli again and as soon as i pulled the glow starter off, the motor died. Put in a new plug did the same thing. Before i make any adjustments to the needles, i thought I would check here to see if I could obtain some suggestions. Like I indicated earlier, lots of heavy smoke and appeared to have a lack in head speed. I'm running powermaster 30% heli. Mid stick pitch 0. All needles are at the factory setting
Thanks

[Rada70]

what shimming are you running? with PoweMaster 30 you need 1600 shims. it sound too rich to me.
Did you use silicone to seal the muffler's header? If so you might have some silicone pits in the engine's head (it happens trust me).

[Lzfalcon]

Rada70,
Do those shims come with the kit? What do you use in place of silicone?

[DavidH]

Shims should have came with motor. I believe an .008 shim is already in place under the head. There should have been an .008 shim also in the box with the engine. So the head would need taken off and the .008 that was in the box installed also along with the .008 that is already under the head.

5 min epoxy works great for sealing between the exhaust flange and the header on a muffler. Just smear it on the header and bolt it to the engine. When it sets up it will form a great seal.

The factoy settings on the needles are most likely to the rich side. You will have to lean the mixture just a little.

David

[Lzfalcon]

davidh,
Thanks for the response. All three needles or the medium and the high?
Thanks

[Lzfalcon]

Just as an FYI, reading the information in the forum about os needle adjustments, I thought i would share my day at the field. I had attempted over the past few days to get my 91sz running correctly. I started out at the field today with the idle at about 5% to the lean and the mid at 3/4 and the high at 2. By the end of the day, I turned the mid all the way in and the high 1 1/2 out, left the idle as it was at 5% to the lean. So far so good. With the mid open I just could not get the high and mid to work together. The only minor issue is if I have the trim to high at Idle, the engine pings a bit like a dirt bike, as soon as i bring the trim down , it goes away. The engine is running at about 130 to 135 after a few climb-outs. by the way, I'm using a Curtis Muscle pipe, 690 vblades, 8.45 gear
Thanks for the help posted above

[Jerry]

845 is not an optimum gearing for the SZ - especially with an MP2.

Closing the midrange is typically only seen on the Hyper version of the SZ. Not that common on the straight carb'ed SZ.

Your engine is pinging like a dirtbike because you have the idle screw on the lean side of stock AND the midrange closed. This combo pretty much equals....dirtbike pinging.

On the Raptor 90, here are your targets with this engine on PM 30%.

Gearing 8.27
Headspeed 1910-1930
.016" to .020" of headshim (stock + 1 thick or stock + 1 thick/1thin)

You aren't seeing a nice transition between mid and high because you probably aren't running the engine within the above parameters.

Be really careful what you read online about SZ needle settings, as they vary greatly between your version, the Hyper PS version, and the Cline modified version.

Jerry

[Rada70]

Jerry, On the SZH cline modified, what would be the correct needle settings?