REFLECTOR: Engine backfiring

[Andrew Ellzey]

Dave,

I had a Mooney M20E that had this engine and flew it for 15 years and about 
600 hours. This engine is known for this problem. The first thing I would 
look at is; there is a 45 degree AN fitting on the bottom of your engine 
that is supposed to be your airbox drain. This 45 degree fitting is supposed 
to have a check valve internal to this fitting. You would never know it is 
installed unless you know that it is there. This is the problem, most people 
think it is a standard AN fitting and will install a new fitting without the 
check valve at overhaul. With the check valve missing your engine sees this 
as an air induction leak and will idle rough and make the backfiring worse. 
A easy way to tell if your valve is working properly is to put your finger 
over the drain line with the engine running and see if you engine lowers its 
idle speed. I have also seen these check valves stuck open and just needs 
cleaning. I tried to order a new check valve when I found that mine had been 
changed out to a standard fitting after fighting this problem for 8 years. I 
never could get a good part number to order one and had to make my own. If 
yours is missing or gone bad I can tell you how to make one. Or you can 
install a PVC valve inline with your drain and it will work just as well. 
The PVC valve should close as your engine sucks air out of your airbox. This 
valve was supposed to drain the excess fuel that drains out of you injectors 
and into your airbox when you shut down your engine and suck closed when you 
start your engine.

Andy Ellzey


----- Original Message ----- 
From: "Dave Philipsen" <velocity at davebiz.com>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Tuesday, August 15, 2006 10:38 PM
Subject: REFLECTOR: Engine backfiring


> Here's a question perhaps for some of the engine experts:  I've got a
> STD FG with IO360-A1A engine.
> It has one standard magneto and one Jeff Rose electronic ignition.  The
> engine and oil cooling are not a
> problem even with OATs in the low 90s. But, I have a problem (it's not a
> huge problem) with backfiring
> during taxi *after* I land.  Taxiing before takeoff seems to be ok.  The
> backfiring happens maybe once
> every 30 seconds or so.  The engine also seems to run a little rough at
> this time.  I've tried running lean,
> running rich, running on just the magneto, running on just the
> electronic ignition.  None of these seems to
> prevent the backfiring during taxi.  The engine never seems to have
> problems before or during takeoff or
> during cruise or descent...just taxiing back after landing.
>
> I'm starting to think it's a vapor lock problem or something since the
> fuel flow is way down and the fuel is
> sitting in the lines longer and heating up.  I had the cowling off the
> other day and was checking the routing
> of the fuel injector lines and they don't appear to be routed near the
> exhaust manifolds or anything like that.
> I was thinking of maybe experimenting with some insulating material
> around the individual injector lines as
> well as the main fuel line.  Any ideas?
>
> -- 
> Dave Philipsen
> STDFG
> N171SP
>
>
> _______________________________________________
> To change your email address, visit 
> http://www.tvbf.org/mailman/listinfo/reflector
>
> Visit the gallery!  www.tvbf.org/gallery
> user:pw = tvbf:jamaicangoose
> Check new archives: www.tvbf.org/pipermail
> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>