OS 91 SZH leaning out few minutes into flight

[Nate Quan]

I am having a bit of a problem with my OS as the title states.

I am flying a tempest 3d with 8.18 gear ratio and an OS 91 SZH, running on cool power 30%. I have not put any head shims in either.

I have 10 flights so far with only 3 or 4 being complete flights. The first couple flights everything was fine until I flipped into Idle1, when I would jump up and down with collective or do a strong climb out the motor would go from smokin good to instantly shuttin down. I continued fattening it up more and more until it was just way to fat with the same result.

Next I eliminated anything that I felt could be restricting fuel flow including a filter and tee ball valve. For about 2 or 3 flights everything was good to go with the motor running consistent through the entire tank.

For about the past 4 or 5 flights everything is good for the first minute or 2 (a little fat if anything) then I can tell that it is leaning out since I feel the power step up as it slowly leans out the I can tell that it gets to lean and starts to get hot, so I land immediately.
This is the first 90 heli I have had, and have never had a problem with my hyper 50's not getting enough fuel, so kinda stumped on which way to go.

[DavidH]

I have not put any head shims in either.

I would start by putting the extra shim in that came with the engine. I believe the SZH needs .016 in head shims when using 30% fuel. The stock shim is .008. There should have been another .008 shim that came with engine and instructions state to add it when using 30% nitro.

Sounds like you might also have some trash in the carb.

David

[heliroller]

Sounds like you are losing fuel flow! What clunk? I run 2 8's on the shims.

[erniefritz]

yep , sounds like your loosing fuel flow...you running muffler pressure? you could do what a lot of people including me do with the SZH , i sent the carb and backplate to James at OMI to tap the backplate and put a cline regulator on the carb and a couple other mods. basically changes the fuel delivery to the same as the YS.... works good.... Viper head will help smooth it out also...

[docjoe]

I had similar things going on with my Stratus and OS-91ZH when I went from 15% to 30%. I did add the extra shim that was in the box and the problem seemed to be resolved.