<<what the Rotax dealer in the UK
describes as 'sub-idle' >>
Which in another language is torsional resonance. Every engine has this,
especially with a larger flywheel (the prop) coupled by a spring (the face
cam device at he front of the gearbox) to the crank.
This natural resonance usually occurs at sub-cranking speeds and is not
excited by the smooth constant-level torque supplied by the starter motor.
The starting system is usually designed to crank the engine above the
resonant speed. Once the engine starts to fire then, if this is at the
resonant speed, the resonance is massively excited. Resonance absorbs a
vast amount of energy so, even if the engine is weakly firing, it may not be
able to "power through" the resonant band.
So the problem could yet be one of the starter not spinning the engine fast
enough to get through this low speed phase; Or improper adjustment of the
preload of the "dog clutch" which effects the resonant frequency. Or
different prop inertia.
Duncan McF.
----- Original Message -----
From: "Pete Lawless" <pete@lawless.info>
Subject: RE: Europa-List: bad cold starts
>
> David
>
> Yes that is exactly what it does. My engine started cold fine but would
> not come up to idle speed. Ran as if only 2 cylinders were firing, very
> rough with lots of vibration. It would take several attempts to get it
> to run smooth. Once it had fired up once then it was ok for the rest of
> the day. I believe it is the kick back that damages the sprag clutch
> but the bad starting, going into what the Rotax dealer in the UK
> describes as 'sub-idle' it the result.
>
> Regards
>
> Pete
>
>
> -----Original Message-----
> From: owner-europa-list-server@matronics.com
> [mailto:owner-europa-list-server@matronics.com] On Behalf Of David
> DeFord
> To: europa-list@matronics.com
> Subject: RE: Europa-List: bad cold starts
>
>
> --> <davedeford@comcast.net>
>
>
> > If it sounds like it is running on 2 cylinders then it could
> > be sprag clutch. Have a look in the archive there is lots of
> > stuff about this. I have just changed my sprag clutch after
> > only 120 hours on a 912 ul. The problem was instantly cured.
> >
> > Pete
>
> Can a sprag clutch problem cause rough running after the starter is off
> (i.e., sprag clutch not disengaging)? I have been ignoring the sprag
> clutch/heavy-duty starter discussion, assuming that it referred only to
> kickback and other problems while the starter was actively driving the
> engine (problems which we haven't experienced).
>
> Thanks to all who have offered suggestions. We have carefully set the
> clutch cables so that both chokes hit their limit stops at the same
> time. We have also checked the temperatures of the exhaust pipes (both
> by feeling and by EGT reading) after a few seconds of rough running, and
> no significant difference was found between the port and starboard
> sides.
>
> Today we tried replacing the fuel in the float bowls with fresh auto
> gas. No help.
>
> After a few seconds of rough running, the port side carburetor sometimes
> overflows fuel into the air box, probably because the float needle gets
> shaken off of its seat. Cylinders 2 and 4 are then quickly flooded,
> which can be overcome only by opening the throttle far too much. We'll
> try starting with the fuel selector off, to see if we can avoid the
> flooding.
>
> Dave DeFord
> N135TD
>
>
> --
>
>
> --
>
>
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