[NSRCA-discussion] OS 140RX rough and inconsistent idle

[mwaustin54 at cox.net]

You might check your bearings. My OS 140 did this after 50 or so flights. New bearings solved the problem. I also run the Mentor head and like the transition.

Mike A.
---- Ed Miller <edbon85 at charter.net> wrote: 
> Have an OS 140RX that has developed a rough and inconsistent idle. Engine 
> runs perfectly except for idle. It has a Mintor head with either an OS F or 
> K&B 1L in center plug and an OS A5 in the angled plug position, a Perf Spec 
> AAC piston/liner assembly and a Boca sealed SS rear bearing. I have the head 
> mounted with angled plug towards the front or carb side of engine. Fuel is 
> S&W 20 nitro, 16 synthetic and 2 castor. Engine has 7 gallons of fuel run 
> through it. Prop is an APC 15.75 x 11 3 blade by Dave Lockhart.  The lowest 
> I can get the idle before it quits is 1900 ~ 2000 rpm and it is rough, 
> sounds like it is firing every other revolution. Idle mixture screw is 
> working, I can richen idle to point where engine will barely transition from 
> being rich and I can lean mixture so the transition is fine but engine slows 
> at idle like it is too rich. While it is slowing with either the idle 
> mixture screw lean or rich, engine is rough, again like it often fires every 
> other revolution at times. I used to be able to reliably idle this engine at 
> 1300 rpm. I have a second OS 140RX set up exactly the same except it doesn't 
> have the AAC piston/liner and it runs/idles perfectly. Tried cleaning the 
> carb/spray bar with no change. I once had a Super Tiger that exhibited 
> similar characteristics due to a worn out con rod.  Is it possible the con 
> rod on this OS could cause this issue ?? Any suggestions will be greatly 
> appreciated.
> Ed M. 
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