Today's Message Index:
----------------------
1. 09:12 AM - Re: 912 80 hp back-fire on shutdown (David Weaver)
2. 06:24 PM - Re: 912 80 hp back-fire on shutdown (Richard Girard)
Message 1
| INDEX | Back to Main INDEX |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: 912 80 hp back-fire on shutdown |
I would suggest, if you have not already checked, to verify that you do not
have partial blockage of a crab idle jet.- If you had complete blockage
of a crab idle jet, the result would be rough engine operation in low engin
e rpm range-due to-failure of crab float function (float bounce).- If
there is-momentary failure of crab float function (engine shaking-will
upset float function)-during flight or at engine shut down, you may get
a miss fire.- I found at one time, following-a 912 installation, where
a very small-flake of fuel hose (probably scuffed off from slipping fuel
hose over a crab fuel line nipple) lodged in a crab idle jet.- Think abou
t it....grounded "P" leads from-ignition switch and an available supply o
f fuel (caused by-engine shaking - float bounce)-expelled from an engin
e cylinder into a hot exhaust pipe.- -I had smooth engine operation in
mid and high rpm-range and rough idle.- I would get one loud back fire
from one
exhaust pipe on shut down.- Thinking that one crab must be flooding out,
I pulled plugs and found nothing unusual.- I had to use a fine wire bris
tle from a wire brush to force the-blockage clear of the idle jet. -Wit
h carburetor equiped 912 I have notice that upon engine shut down at too hi
gh of an idle rpm-may cause the engine to-run on a few extra revolution
s.- I get the smoothest shut down when pulling the idle rpm down to about
1700 and then turn the ignition switch off.- Although not frequent,-I
have noticed that when flying in-rough air that just for an instant engin
e operation is interrupted by a slight hic-up.- Not a miss fire, but just
a momentary change in rpm.- I suspect that is due to carb float bounce a
nd have learned to accept perfection is not to expected in all things mecha
nical.
Dave Weaver
--- On Sat, 1/28/12, Richard Girard <aslsa.rng@gmail.com> wrote:
From: Richard Girard <aslsa.rng@gmail.com>
Subject: Re: RotaxEngines-List: 912 80 hp back-fire on shutdown
There are two distinct and opposing conditions that could cause your engine
to backfire. Too rich an idle mixture letting unburned fuel slip by the va
lves into an exhaust system already heated by high EGT's when the power is
pulled back on approach. Or the mixture is too lean and it's on the verge o
f running on after the ignition is shut off.(my Harley used to do this on w
arm up when I pulled the choke off too early).
What is your idle RPM before the stabilization run? Is it different after t
he stabilization run?
If your heart can stand the strain, let it backfire one last time and immed
iately look at the plugs. Do the same after a stabilization run and note if
there's any difference.
Rick Girard
On Sat, Jan 28, 2012 at 4:58 PM, ejessee <eejessee@us.ibm.com> wrote:
Hello all,
I did a search in the forum with "backfire", "back-fire", and "back fire" w
ith no results, So here goes....
I have an 80 hp 912 UL on a Zenith 701. -When I return to my hangar after
flight, unless I do a 2 -3 minute stabilization run at 2100 RPM, my 912 ba
ckfires like a shotgun when I turn it off. -I have newly rebuilt carbs, p
erfectly balanced carbs, plugs at .024. -The engine runs perfect, uses no
oil. -My exhaust stacks are heat-wrapped. -As severely as it backfires
, I am afraid I am going to damage my exhaust system.
Anyone else ever experience this? -Anybody know what is causing it. -Is
something wrong or is this just the nature of the engine.
AS always, thanks for your help. -This forum is a fantastic resource.
--------
Ernest Jessee
N4931M
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=365064#365064
-List" target="_blank">http://www.matronics.com/Navigator?RotaxEngines-Li
st
http://forums.matronics.com
le, List Admin.
="_blank">http://www.matronics.com/contribution
--
Zulu Delta
Mk IIIC
Thanks, Homer GBYM
It isn't necessary to have relatives in Kansas City in order to be unhappy.
- - Groucho Marx
Message 2
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: 912 80 hp back-fire on shutdown |
David, I think it's rude to accuse a man you don't even know of having
crabs. :-} Couldn't help myself, no offense intended.
Rick
On Sun, Jan 29, 2012 at 11:09 AM, David Weaver <mortweaver@sbcglobal.net>wrote:
> I would suggest, if you have not already checked, to verify that you do
> not have partial blockage of a crab idle jet. If you had complete blockage
> of a crab idle jet, the result would be rough engine operation in low
> engine rpm range due to failure of crab float function (float bounce). If
> there is momentary failure of crab float function (engine shaking will
> upset float function) during flight or at engine shut down, you may get a
> miss fire. I found at one time, following a 912 installation, where a very
> small flake of fuel hose (probably scuffed off from slipping fuel hose over
> a crab fuel line nipple) lodged in a crab idle jet. Think about
> it....grounded "P" leads from ignition switch and an available supply of
> fuel (caused by engine shaking - float bounce) expelled from an engine
> cylinder into a hot exhaust pipe. I had smooth engine operation in mid
> and high rpm range and rough idle. I would get one loud back fire from one
> exhaust pipe on shut down. Thinking that one crab must be flooding out, I
> pulled plugs and found nothing unusual. I had to use a fine wire bristle
> from a wire brush to force the blockage clear of the idle jet. With
> carburetor equiped 912 I have notice that upon engine shut down at too high
> of an idle rpm may cause the engine to run on a few extra revolutions. I
> get the smoothest shut down when pulling the idle rpm down to about 1700
> and then turn the ignition switch off. Although not frequent, I have
> noticed that when flying in rough air that just for an instant engine
> operation is interrupted by a slight hic-up. Not a miss fire, but just a
> momentary change in rpm. I suspect that is due to carb float bounce and
> have learned to accept perfection is not to expected in all things
> mechanical.
> Dave Weaver
>
> --- On *Sat, 1/28/12, Richard Girard <aslsa.rng@gmail.com>* wrote:
>
>
> From: Richard Girard <aslsa.rng@gmail.com>
> Subject: Re: RotaxEngines-List: 912 80 hp back-fire on shutdown
> To: rotaxengines-list@matronics.com, kolb-list@matronics.com
> Date: Saturday, January 28, 2012, 11:33 PM
>
> There are two distinct and opposing conditions that could cause your
> engine to backfire. Too rich an idle mixture letting unburned fuel slip by
> the valves into an exhaust system already heated by high EGT's when the
> power is pulled back on approach. Or the mixture is too lean and it's on
> the verge of running on after the ignition is shut off.(my Harley used to
> do this on warm up when I pulled the choke off too early).
> What is your idle RPM before the stabilization run? Is it different after
> the stabilization run?
> If your heart can stand the strain, let it backfire one last time and
> immediately look at the plugs. Do the same after a stabilization run and
> note if there's any difference.
>
> Rick Girard
>
> On Sat, Jan 28, 2012 at 4:58 PM, ejessee <eejessee@us.ibm.com<http://us.mc827.mail.yahoo.com/mc/compose?to=eejessee@us.ibm.com>
> > wrote:
>
> >
>
> Hello all,
> I did a search in the forum with "backfire", "back-fire", and "back fire"
> with no results, So here goes....
>
> I have an 80 hp 912 UL on a Zenith 701. When I return to my hangar after
> flight, unless I do a 2 -3 minute stabilization run at 2100 RPM, my 912
> backfires like a shotgun when I turn it off. I have newly rebuilt carbs,
> perfectly balanced carbs, plugs at .024. The engine runs perfect, uses no
> oil. My exhaust stacks are heat-wrapped. As severely as it backfires, I
> am afraid I am going to damage my exhaust system.
>
> Anyone else ever experience this? Anybody know what is causing it. Is
> something wrong or is this just the nature of the engine.
>
> AS always, thanks for your help. This forum is a fantastic resource.
>
> --------
> Ernest Jessee
> N4931M
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=365064#365064
>
>
> ==========
> -List" target="_blank">
> http://www.matronics.com/Navigator?RotaxEngines-List
> ==========
> http://forums.matronics.com
> ==========
> le, List Admin.
> ="_blank">http://www.matronics.com/contribution
> ==========
>
>
> --
> Zulu Delta
> Mk IIIC
> Thanks, Homer GBYM
>
> It isn't necessary to have relatives in Kansas City in order to be unhappy.
> - Groucho Marx
>
>
> *
>
> ist" rel=nofollow target=_blank>http://www.matronics.com/Navigator?RotaxEngines-List
> et=_blank>http://forums.matronics.com
> llow target=_blank>http://www.matronics.com/contribution
> *
>
> *
>
> *
>
>
--
Zulu Delta
Mk IIIC
Thanks, Homer GBYM
It isn't necessary to have relatives in Kansas City in order to be unhappy.
- Groucho Marx
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|