Matronics Email Lists :: View topic - Backfire or Afterfire

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

Backfire or Afterfire

Matronics Email Lists Forum Index -> Zenith-List

View previous topic :: View next topic

Author Message

george.mueller(at)aurora.
Guest

Posted: Tue Sep 04, 2007 6:00 am Post subject: Backfire or Afterfire

I am at the point of doing full power run-ups with my Zenith 701 with a rotax 912 UL 80hp installed with a Skyshops firewall forward kit.  When I do a full power run up, I get a backfire (or afterfire maybe) after I turn the ignition key to "off".  When I taxi around keeping the engine to around 2,000 rpm, this does not happen after shutdown, only after I do a full power run-up.  Everything else seems normal as far as I can tell, the engine starts really well, seems to run smoothly, idles well.  But after doing three full power run ups, I have had three backfires, all after turning off the ignition.  Does anyone on the list have an idea about what might be causing this? 

 

 

George in Milwaukee 

701 912UL [quote][b]

Jari Kaija

Joined: 23 Feb 2006
Posts: 69

Posted: Tue Sep 04, 2007 6:53 am Post subject: Backfire or Afterfire

You are doing WHAT! Turning off ignition, while  engine runs at maximum speed?

 What kind of test is this? Newer heard and I  have quite a lott of experience with

 single piston aeroplanes, since I got my PPL  license -96! 

  

 Don't destroy your engine. 

  

 Think a while! When you turn ignition off and  engine have such kind of

 rpm. All gasoline/air mix will flow to muffler,  because that mix didn't

 blow out in the cylinders. And muffler, when there  is enough gas/air mix 

 in a hot "steel botle", WILL catch fire!!!!

  

 [quote]   ---

Jari Kaija

Joined: 23 Feb 2006
Posts: 69

Posted: Tue Sep 04, 2007 6:55 am Post subject: Backfire or Afterfire

...or did you mention fire in the carburetor's  intake?

   [quote][b]

klr12(at)psu.edu
Guest

Posted: Tue Sep 04, 2007 8:04 am Post subject: Backfire or Afterfire

Mr. Pilot,

  Ever hear of  AD 76-07-12, BENDIX IGNITION SWITCHES?

                                                                                                KLR

     [quote][b]

601zv(at)ritternet.com
Guest

Posted: Tue Sep 04, 2007 8:40 am Post subject: Backfire or Afterfire

I believe he clearly said "AFTER I do a full  power run-up," not DURING.

  

 Do not archive.

 [quote]   ---

Trainnut01(at)aol.com
Guest

Posted: Tue Sep 04, 2007 10:10 am Post subject: Backfire or Afterfire

When I was involved with Nascar during the eighties several times during  each weeks testing we would do a "Plug check"  The procedure required the  driver to run several hot laps, then right at the end of the back straight he  would turn off the ignition (at full throttle), take the car out of gear, and  coast to the pits. The crew would then push the car back to the garage, quickly  remove the sparks plugs and rush them to the Champion Spark Plug trailer to have  them "read" by the Champion Rep. The plugs were then returned to us with  notations as to which ones should have gaskets added and which ones should have  gaskets removed. Apparently the plug temp can be controlled by gasket thickness.  I did not understand this at the time (not in my job description) and I don't  understand it now but I do know that cutting the ignition at full throttle told  somebody something.

 Carroll

  

 do not archive



Get a sneak peek of the all-new AOL.com.

  [quote][b]

crvsecretary

Joined: 18 Mar 2007
Posts: 38
Location: Naugatuck, CT

Posted: Tue Sep 04, 2007 11:08 am Post subject: Backfire or Afterfire

I've heard of this procedure to check the size of the main jet in the  carburator and the heat range of the plug.  Adding & removing  gaskets might change the amount of heat the plug can shed to the cylinder  head, but typically heat range is built into the plug.

  

 Tracy Smith

 Naugatuck, CT

 Do Not Archive

  

  

  

 In a message dated 9/4/2007 1:11:10 PM Eastern Standard Time,  Trainnut01(at)aol.com writes:

  	  Quote: 	
		     When I was involved with Nascar during the eighties several times during    each weeks testing we would do a "Plug check"  The procedure required the    driver to run several hot laps, then right at the end of the back straight he    would turn off the ignition (at full throttle), take the car out of gear, and    coast to the pits. The crew would then push the car back to the garage,    quickly remove the sparks plugs and rush them to the Champion Spark Plug    trailer to have them "read" by the Champion Rep. The plugs were then    returned to us with notations as to which ones should have gaskets added and    which ones should have gaskets removed. Apparently the plug temp can be    controlled by gasket thickness. I did not understand this at the time (not in    my job description) and I don't understand it now but I do know that cutting    the ignition at full throttle told somebody something.

   Carroll

    

   do not archive

    

	


 

  



Get a sneak peek of the all-new AOL.com.

_________________
Zenith 601XL N458XL (reserved)
Naugatuck, CT
Tail Complete; working on wings

dougsnash(at)yahoo.com
Guest

Posted: Tue Sep 04, 2007 11:41 am Post subject: Backfire or Afterfire

George, I have a similar set up but am still about six

months away from run-ups.  That being said, sounds

like you could have a mixture issue (running rich and

loading up the exhust with unburned fuel) but I would

be more suspicious of fuel quality.  Maybe try a

different souce for your fuel.  Might be stale fuel or

something.



Food for thought at least.



Doug MacDonald

CH-701 Scratch Builder, 912 UL

NW Ontario, Canada

Working on throttle assy.

--- george.mueller(at)aurora.org wrote:



 	  Quote: 	
		   I am at the point of doing full power run-ups with

 my Zenith 701 with a 

 rotax 912 UL 80hp installed with a Skyshops firewall

 forward kit.  When I 

 do a full power run up, I get a backfire (or

 afterfire maybe) after I turn 

 the ignition key to "off".  When I taxi around

 keeping the engine to 

 around 2,000 rpm, this does not happen after

 shutdown, only after I do a 

 full power run-up.  Everything else seems normal as

 far as I can tell, the 

 engine starts really well, seems to run smoothly,

 idles well.  But after 

 doing three full power run ups, I have had three

 backfires, all after 

 turning off the ignition.  Does anyone on the list

 have an idea about what 

 might be causing this?

 

 

 George in Milwaukee

 701 912UL

planecrazydld(at)yahoo.co
Guest

Posted: Tue Sep 04, 2007 12:06 pm Post subject: Backfire or Afterfire

The only way to get an accurate and readable color condition on the plug is to shut down at high throttle. Allowing the engine to come down through the rpm and power bands will contaminate the purity og the data to be extracted by "reading" the plugs. I am fascinated by the gasket shifting though; what was being learned/accomplished there?

 

  Dave Downey

 Harleysville (SE) PA

 100 HP Corvair



 



 ---

n801bh(at)netzero.com
Guest

Posted: Tue Sep 04, 2007 3:52 pm Post subject: Backfire or Afterfire

I drove those things back in the eighties and also built a few motors for them too.  I read my own plugs to determine fuel mixture but more critical was looking for proper ignition timing. I still do it every few months as my plane has a NASCAR style motor in it. It took me a couple of times of explaining to the control tower why I would actually shut off a good running motor about half way down the runway at full throttle. <G> The backfire is caused by unburned fuel in the exhaust system, it is lit off by either the glowing exhaust valves or some real hot carbon build up in the pipes. All well built engines are dyno run before they get to the track and changing plug gaskets will "index"the ground strap on the plug to get optimal combustion. The slight difference in fuel mixture between cylinders is usually tweaked during flow testing of the intake manifold and intake ports on a flow bench, this happens before the motor isassembledAfter reading the plugs I would determine if the timing is correct, then I would make a jet change if needed and as a last result I would make a spark plug heat range change.If the original poster would let the motor cool a few minutes before shutting off the ignition it will probably not backfire. 

Do not archive



 When I was involved with Nascar during the eighties several times during each weeks testing we would do a "Plug check"  The procedure required the driver to run several hot laps, then right at the end of the back straight he would turn off the ignition (at full throttle), take the car out of gear, and coast to the pits. The crew would then push the car back to the garage, quickly remove the sparks plugs and rush them to the Champion Spark Plug trailer to have them "read" by the Champion Rep. The plugs were then returned to us with notations as to which ones should have gaskets added and which ones should have gaskets removed. Apparently the plug temp can be controlled by gasket thickness. I did not understand this at the time (not in my job description) and I don't understand it now but I do know that cutting the ignition at full throttle told somebody something.

 Carroll

  

 do not archive

         

      

 The only way to get an accurate and readable color condition on the plug is to shut down at high throttle. Allowing the engine to come down through the rpm and power bands will contaminate the purity og the data to be extracted by "reading" the plugs. I am fascinated by the gasket shifting though; what was being learned/accomplished there?

 

  Dave Downey

 Harleysville (SE) PA

 100 HP Corvair



   /aolcom30tour/?ncid=AOLAOF00020000000982 href="http://discover.aol.com/memed/aolcom30tour/?ncid=AOLAOF00020000000982" target=_blank>AOL.com.

[quote]



====================================

">http://www.matronics.com/Navigator?Zenith-List

====================================

tronics.com

====================================



[b]

vgstol(at)bigpond.net.au
Guest

Posted: Tue Sep 04, 2007 4:01 pm Post subject: Backfire or Afterfire

And make certain the throttle is  held completely closed and the idle slowed right down.   

 Do not archive.

 JG

 [quote]   ---

ashontz

Joined: 27 Dec 2006
Posts: 723

Posted: Wed Sep 05, 2007 6:34 am Post subject: Re: Backfire or Afterfire

Apparently heat is involved. I'm sure the engine is a lot hotter after a full power run up. Even so, you really shouldn't be shutting down and engine at full power. I don't think it will hurt the engine, unless a backfire blows out a gasket somewhere, but even so, there's no reason to be shutting down at full power.



Looking at a fellow builders 912 I can see that the carbs on those things aren't very complicated. It's not like a car engine that has an O2 sensor and all kinds of other engine management systems. That being said, it's easy to create a situation where you can fool the engine into behaving badly. An airplane engine isn't meant to be much more than an adjustable oversized lawner engine. It provides power, but it's not meant to be revved up and down and all over. It's meant more for slower, more controlled inputs.



Even so, they sell some pretty cool engine diagnostic tools these days, inline mixture meters as well as special temporary spark plugs that are mae with see-through glass that you can actually see the flame inside the cylinder. Another cheap method is to go down to Autozone and get a $25 O2 sensor, install it in the exhaust and hookup a volt meter to it and the O2 sensor will send back a voltage that is calibrated to indicate O2 levels in the exhaust. If you take a O2 sensor and put it in a vise and hookup an ohmmeter it will read (I believe) infinate ohms when cold and just outside air, heat it up with a propane torch and the reading goes to like 1k ohms or something like that. It needs to be hot to operate correctly, but the combination of the heat and the blue torch flame (no oxygen left because it's fully burned) moves the ohmmeter full range. In a car, that's what controls the mixture, the O2 sensor sends the signal to the carb and the carb adjusts the mixture several times per second. You could easier install a gauge on the instrument panel to show what the O2 sensor sees and calibrate it, all for about $35.



[quote="george.mueller(at)aurora."]I am at the point of doing full power run-ups with my Zenith 701 with a rotax 912 UL 80hp installed with a Skyshops firewall forward kit.  When I do a full power run up, I get a backfire (or afterfire maybe) after I turn the ignition key to "off".  When I taxi around keeping the engine to around 2,000 rpm, this does not happen after shutdown, only after I do a full power run-up.  Everything else seems normal as far as I can tell, the engine starts really well, seems to run smoothly, idles well.  But after doing three full power run ups, I have had three backfires, all after turning off the ignition.  Does anyone on the list have an idea about what might be causing this? 

 

 

George in Milwaukee 

701 912UL  	  Quote: 	
		  [b]

Display posts from previous:

	Matronics Email Lists Forum Index -> Zenith-List	All times are GMT - 8 Hours
Page 1 of 1

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum