REFLECTOR: Engine backfiring

[Dave Dent]

Your right I have seen this before.  Some call it the riffle valve. Manifold 
drain valve.  I have encountered this valve missing and one time causing a 
fire.  The fuel didn't drain out and it back fired and lit off.
Good Call Andy
Dave
----- Original Message ----- 
From: "Andrew Ellzey" <ajlz72756 at yahoo.com>
To: <velocity at davebiz.com>; "Velocity Aircraft Owners and Builders list" 
<reflector at tvbf.org>
Sent: Tuesday, August 15, 2006 9:44 PM
Subject: Re: REFLECTOR: Engine backfiring


> 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
>>
>>
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