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

[Lance Van Nostrand]

Ed,
I don't have any experience with the Perf Spec sleevel, but I assume it was 
running fine and then went south.  Rough running usually means leaks or 
misfits.  Pulling the piston to inspect the play in the wrist pin/conrod is 
easy.  There should be almost none.  Be sure to look carefully at the piston 
bosses holding the wrist pin.  I have seen several well used engines that 
will acutally wear out the piston bosses.  Check head bolts and look for 
external leaks.  A test stand is good for this as you can see leakage 
easier.  The carb barrel fit is very critical.  The carb barrel/housing is 
machined to extremely tight tolerances.  look for any wear.  a piece of dirt 
can break the seal if it has worn a groove.  Make sure the little O-rings in 
the carb are not worn.  It should compression lock with no leaks with a 
little fuel in the carb during reassy.

Good Luck.
--Lance

----- Original Message ----- 
From: "Ed Miller" <edbon85 at charter.net>
To: "NSRCA Mailing List" <NSRCA-discussion at lists.nsrca.org>
Sent: Monday, June 26, 2006 5:17 AM
Subject: [NSRCA-discussion] OS 140RX rough and inconsistent idle


> 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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