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Fuel in the FAB

LettersFromFlyoverCountry

Well Known Member
Here's the looks of things when I took off the FAB for the conditional, on an IO-360-M1B.

fab_1.jpg


fab_2.jpg


What can cause accumulation of 100L?
 
I hope he is not pumping the throttle while starting an injected engine. If you are, don't

I think you have a leak in your servo. I would pressurize the system with the throttle closed and the mixture in the rich position. Examine the throttle and mixture barrels, these O rings may need changing.
 
Starting technique is as Mattituck said:

Throttle full open
Mixture full open
Boost pump 5 seconds
Throttle full closed
Mixture to cutoff
Boost pump off
Throttle 1/8
Engage starter
 
Same thing

I posted a thread a few weeks ago. I tend to get the same thing, it looks like some oil mixing in with the fuel, make a thick blueish film. No one seemed to have any ideas or noted that this was normal. I am continuing to fly since things are working normally and I can't find what the deal might be.

I was told I might be over priming, I was using 5 sec per the Air Flow Performance (AFP) instructions, for a cold start, none or 2 sec for a hot start.

I look forward to what others reply here. This is a shot of mine right after the FAB came off. Mine has a heavier build up than yours. I can see where one might over prime but why would it not get sucked back up into the engine.

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Maybe Don from AFB will see this and shed some light, could be fuel settling after shutdown.

Cheers
 
Starting technique is as Mattituck said:

Throttle full closed
Mixture full open
Boost pump 5 seconds
Throttle full closed
Mixture to cutoff
Boost pump off
Throttle 1/8
Engage starter

My changes to your technique in red

This is my hot start technique

The cold start process leaves the mixture in full rich, all else is the same. In either case the throttle is only opened just prior to starter engagement.
 
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Starting technique is as Mattituck said:

Throttle full open
Mixture full open
Boost pump 5 seconds
Throttle full closed
Mixture to cutoff
Boost pump off
Throttle 1/8
Engage starter

I use this same procedure for cold starts with my IO-540 in my RV-10 and I find the same kind of residue in the FAB. It comes from fuel running back down the intake tubes during this start procedure. I'm going to try Tadsargent's method of keeping the throttle closed during fuel pump run. It seems like this method might take longer to start but I don't think it would cause fuel residue in the FAB.

Kevin Belue
RV-6A
RV-10
 
This is not unusual for a fuel injected engine. If the sniffle valves are not at the lowest points of the induction system you will get fuel in the airbox. With a vertical servo and stock sump there are no sniffle valves. As fuel boils out of the injector lines after shutdown small streams of fuel flow down the intake tubes and end up at the lowest points of the system. The gurgling sound you typically hear on a FI engine after shutdown is the fuel boiling out of the injector lines.

The stains build up over time making it appear like there is more leakage then there actually is.
 
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What Bob said....and do not over prime, 5 seconds is far too long no matter who said it in their manuals ;)
 
I've seen this forever in mine. As the weather gets colder, one will need more prime prior to cranking if you want it to fire off after a couple blades. At idle, so little air is flowing up the induction tubes that it will not pull the extra fuel up hill. Additionally, as someone else posted, the fuel in the flow distributor and lines dumps into the engine once it is shutdown. If you are not running a purge valve, there will be additional fuel which might boil up from the servo and connecting hose.

I drilled a hole in the bottom of the FAB, inside the aft end of the filter, to allow the goo to drain. I glued a fitting on the bottom side of this hole, onto which I have a hose attached to dump the stuff behind the cowl aft end.

5 seconds with the throttle at idle will not be enough to start my engine without a fair bit of cranking, btw (AFP system).
 
I'm flying behind a 200 HP angle valve IO-360 with Bendix FI.

If I ever opened the throttle and mixture full, and ran the pump for 5 full seconds, my engine would be totally flooded with fuel pouring out the sniffle valve.

For cold start (starts on 2nd blade usually):
mixture full rich
throttle cracked 1/4 inch or so
boost pump on for 2-3 seconds then off
start

For hot start (starts after 3-4 seconds of cranking):
mixture idle cusoff
throttle cracked 1/4 inch or so
start
open mixture as engine catches.

I imagine the smaller FI engines are similar.
 
Priming

200 Hp IO-360 Angle Valve:

What works for me for a cold start is:

Full Throttle
Full Mixture
2-3 seconds boost pump (warm weather); 3-4 seconds boost pump (cool weather*)
Pump Off
Mixture-ICO
Throttle-Slightly cracked open
Hit the starter & advance the mixture as it catches. Fires on 1-2 blades every time (with mags)

*Cool weather by SoCal standards = 50-60 degrees.

Skylor
RV-8
 
I've seen this forever in mine. As the weather gets colder, one will need more prime prior to cranking if you want it to fire off after a couple blades. At idle, so little air is flowing up the induction tubes that it will not pull the extra fuel up hill. Additionally, as someone else posted, the fuel in the flow distributor and lines dumps into the engine once it is shutdown. If you are not running a purge valve, there will be additional fuel which might boil up from the servo and connecting hose.

I drilled a hole in the bottom of the FAB, inside the aft end of the filter, to allow the goo to drain. I glued a fitting on the bottom side of this hole, onto which I have a hose attached to dump the stuff behind the cowl aft end.

5 seconds with the throttle at idle will not be enough to start my engine without a fair bit of cranking, btw (AFP system).

I am with you Alex, AFP fuel injection. I tried using less than 5 sec prime on a cold engine and it takes a lot longer to start.

I have a drain hole on the low spot on the FAB, I never thought to run a drain hose.
 
I am with you Alex, AFP fuel injection. I tried using less than 5 sec prime on a cold engine and it takes a lot longer to start.

That's because FF with no airflow thru the servo is practically 0 with the throttle closed, full throttle allows the fuel to flow at about a 4GPH rate. About 1-2 secs with full throttle works perfect for me.
 
Fuel in FAB

What Bob said....and do not over prime, 5 seconds is far too long no matter who said it in their manuals ;)

I am using 3 seconds pump on start. The engine still starts after a few blades.
Fuel stains still in the FAB. On occasion I have flooded on hot starts causing fuel in the FAB to leak down through the FAB's aux air onto the bottom cowl.
Not a good thing as the fuel does a great job dissolving the glue holding my heat shield (foil) on the cowl :eek:
 
The mixture control can also be leaky so that when you go to full lean, it still lets a bit of fuel by. If there is residual fuel pressure or if you have the electric pump on after shutdown, fuel can leak by the mixture valve and continue to flow out of the nozzles. The Bendix RSA series had AD's on them for leakage at the mixture valve. The Airfolw Performance servos use a different valve arrangement and do often leak by also. I an AFP one a while back which was leaky, which at that time AFP had said was normal.
 
In in the 2 to 3 second prime group and have not had any issues with starting. I also have fuel drain out of the cowl down the front gear fairing onto the front wheel pant! Done it forever and can't find any source other than back out the servo and out my snorkel drain hole after shutdown.
 
Sometimes the servo is just plain broken. To test it plug the fuel line at the flow divider and open the mixture and throttle full. Turn on the fuel pump and while it is running check that no fuel is coming out of the impact tubes. If there is send it to your favorite fuel system fixen place. That is something that should be done every year.
 
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