REFLECTOR: Engine backfiring

[Ron Brown]

And look for any other sources of intake air leaks.

We had a 172 that was doing something very similar at idle - a pop every 
once in awhile when idling.  We found one of the rubber sleeves that joins 
the intake runner at the oil sump to the runner goes to the cylinder 
mispositioned.  This rubber sleeve doesn't exist on our IO 360's but any 
leak in an intake runner to the cylinder head gaskets or servo mount to the 
oil pan can do the same thing.  It was a very small air leak, but just 
enough to make it pop every 30 seconds to a minute.

Ronnie




----- Original Message ----- 
From: "Dave Philipsen" <velocity at davebiz.com>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Wednesday, August 16, 2006 10:46 PM
Subject: Re: REFLECTOR: Engine backfiring


> Ok, I tried the suggestion today of running the aux. fuel pump while
> taxiing with the engine hot.  It did not completely eliminate the
> backfiring but I think it was reduced by maybe 50% or more.  Definitely
> appeared to make an improvement.  It looks like you might have me on the
> right track here.  I'm also going to check the "wiffle" valve and the
> insulation under the spider.
>
>
> Scott Derrick wrote:
>> This is usually a common problem caused by overheating the injection
>> lines and spider, its especially prevalent in updraft engines.  Heating
>> the injection system can help when running at cruise but can be a
>> problem at idle if its too hot.
>>
>> If  the problem is just a hot injection system you can sometimes
>> alleviate it by doing a couple things.
>>
>> 1.)  Run your aux fuel pump while taxing if the engine is hot. The
>> higher pressure can prevent some of the fuel from vaporizing.
>>
>> 2.) Put an insulated baffle under the spider so it doesn't absorb as
>> much ambient heat from the engine case.
>>
>> 3.) some folks run a 1/2 inch cooling  duct  to the spider and build a
>> shroud around the spider to direct the air. This can help with the over
>> heating problem but it also cools the fuel when running which may lower
>> fuel efficiency, probably by not much though.
>>
>> My  TSIO520 has a  heated spider that  is heated with an oil line. This
>> keeps the spider at oil temp which is good for fuel burn but also helps
>> prevent it from getting so hot the fuel vaporizes.
>>
>> Scott
>>
>
> _______________________________________________
> 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