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HomeRC & Power✈️Aircraft🚁HelicopterEngines Plugs Mufflers Fuel › OS. 91 SZH with pump mods ?
09-07-2006 02:24 AM  14 years ago
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Jdonovan

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Louisville, Ky

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OS. 91 SZH with pump mods ?
Is james Oneal (OMI) Doing any mods for the pumped version of the szh.
Or is this engine the cats meow without any mods. Its seems any time he does any mods the motors run better or produce more power.
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09-07-2006 04:05 PM  14 years ago
Jerry Sudimick

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Connecticut

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He is not modifying the pumped 91SZ.

Jerry
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09-10-2006 06:01 PM  14 years ago
Razz

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Louisville, KY

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Hey Jerry,
I have a question for you, since your the engine doctor! I have been running a SZ OMI, Viper head .024 shim's (2 OS 8's),with an SB17. I have 15 gallons through the engine, and overall the engine has performed really well. I removed it from an Avant I'm selling, and was looking over the engine...the main bearing looks great, I was expecting a little slop, and some corrosion, but it's very clean(using curtis blend 30%). How many gallons can I expect to run before I may need to replace the bearings? The extra stiffness of the crankcase must be playing it's part here, and reducing bearing wear. I had a YS which needed bearings at the 10 gallon point.

Also, James gave me two different cateyes for the carb., I have been using the stock SZ with good results which has a smaller cateye than the Cspec cateye. I still occasionally have some roughness in the midrange. If I lean the hover needle a few extra clicks, I get a better throttle response in the midrange, but end up with some roughness. If I go the other route and richen the hover needle, I get slower throttle response, but slightly smoother.

I thought maybe you have been down this road before, any thoughts? I'm running a 8.08 gear ratio, HS at 1850.

Thanks,
Brian Rasmussen
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09-10-2006 06:43 PM  14 years ago
Razz

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Louisville, KY

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Jerry,
I just looked at your gallery with all your nice pic's of the OS91 carb. I guess the smaller cateye is prefered with the cline. I did initially use the larger cateye when I first got the engine, and I had to run my needles much leaner for idle and hover. I did not spend more that a couple flights with it, as my needles were turned in much more that most pilots.

I thought maybe I would find that total 'sweet spot' in the midrange using the larger cateye, and closing down the needles somewhat.

Brian
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HomeRC & Power✈️Aircraft🚁HelicopterEngines Plugs Mufflers Fuel › OS. 91 SZH with pump mods ?
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