What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Fire in the hole...

Walt

Well Known Member
Actually in the airbox, vertical induction FI with no drain holes for excess fuel to escape. I saw another similar situation that caused a lot more damage, this one escaped with some minor air cleaner and fiberglass damage.

Airbox's (both carb and FI) need drain holes, I put 3 in, one in front and one behind the air cleaner for rain and such and another in the center of the filter to drain excess fuel that may accumulate there (tail draggers get the hole towards the rear).

This one will get the standard metal plate in the bottom repair as the fiberglass is also worn thru in a couple spots.

2019052517261145-IMG_0651-XL.jpg
 
Last edited:
And this exact scenario was described in Vic Syracuse's seminar which I just watched.

Ya beat me to it. :) Great presentation by Vic, for sure. A variety of other important things to watch out for in maintenance and inspections that he points out, and it's not only loose jam nuts!
 
This is what the sniffle valve is for in horizontal induction sumps.

I sometimes worry that for a taildragger, the sniffle valve is not quite in the best location. But it can not accumulate very much.
 
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.
 
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

Carb:
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.
 
Last edited:
Back
Top