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Old 05-27-2019, 12:32 PM
JonJay's Avatar
JonJay JonJay is offline
Join Date: Jan 2007
Location: Battleground
Posts: 4,179

Originally Posted by JonJay View Post
What caused the fire?
Ok, assuming back fire into rich airbox.
After several reports of this occurring, with or without drain holes, I modified my cold start procedure. I no longer prime my injected engine, which can dump fuel into the airbox. I simply crack throttle, mixture rich and then backed off a few turns, hit the boost pump, listen for pump to load (two seconds or so), then crank.
Starts within 6 or 8 blades. Doesn’t cough and choke like it used and risk of an airbox explosion event is reduced or perhaps eliminated.
Hot Starts are done the same way with the exception that the mixture is closed, no boost pump, throttle cracked, start cranking, and advance mixture slowly and it will fire.
Smart People do Stupid things all the time. I know, I've seen me do'em.

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Old 05-27-2019, 01:42 PM
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Walt Walt is offline
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,132

A few basic operational procedures to help prevent this:

For FI:
Cold: Do no overprime, a couple of seconds with mix/throt all in is plenty, (you can always add more if it doesn't catch).
Hot: No prime as engine is more than likely already flooded, only add fuel after you're sure it's cleared

Cold: pump the throttle only while cranking as the accelerator pump shoots a nice stream of fuel out every time you work the throt.
Hot: no throttle pumping need, carbs are generally easy starters when hot.

For both: if you engine doesn't crank normally you are much more likely to have a backfire, engines that crank good rarely backfire.

Make sure your timing is correct if you're having backfires, backfires are not normal. Check your non impulse mag is not firing while cranking.

If you do have a backfire don't add fuel and continue cranking trying to get it started, a running engine will put out an airbox fire.
Walt Aronow, DFW, TX (52F)

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Last edited by Walt : 05-27-2019 at 01:45 PM.
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