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Fuel from manifold HELP!

3

330drvr

Active Member
We were doing a leak check at the end of the annual condition inspection. With the throttle open, fuel pump on and mixture full rich, I had fuel coming out of the #4 intake manifold (at the gasket) and eventually out of the air box. I have the Silver Hawk EX-5VA1 on an IO-360. The spark plug was dry. Clearly I will replace the intake gaskets, but what has caused this? I suspect a problem with the "flow divider" (where the injector lines come from) but is this likely? Any comments appreciated.
 
new gaskets...

Want to get in on an order of new gaskets? :)

http://www.vansairforce.com/community/showthread.php?t=120151

I'm not a fuel system expert...but I don't see why the fuel flow divider would be an issue. I believe the dividers purpose is to divide the fuel to the nozzles and to ensure the fuel flow stops at Idle-Cutoff.

I have the same FI system as you and what you are describing is how I prime for starting with throttle/mixture and pump...so why wouldn't the fuel be dumping into the manifold?
 
With the mixture rich, throttle open and boost pump on, you were dumping copious amounts of fuel into the intake port. The fact that a bunch of fuel ended up puddling in the airbox is not a surprise, but leaking out of the intake gasket indicates a problem with the gasket seal, not the fuel system.
 
Thanks for the comments. It was just SO much fuel (like a major fire hazard) that caught me off guard. If I can fix with 4 new manifold gaskets, that sounds great! (And inexpensive)
 
Toobuilder said:
With the mixture rich, throttle open and boost pump on, you were dumping copious amounts of fuel into the intake port. The fact that a bunch of fuel ended up puddling in the airbox is not a surprise, but leaking out of the intake gasket indicates a problem with the gasket seal, not the fuel system.
Click to expand...

Correct...
 
330drvr said:
Thanks for the comments. It was just SO much fuel (like a major fire hazard) that caught me off guard. If I can fix with 4 new manifold gaskets, that sounds great! (And inexpensive)
Click to expand...

You should really study the "how it works" documentation on your fuel system. If this surprised you, imagine your surprise when you flood it and have a starting backfire. You do have a sniffle valve, right?

These injectors do not pulse (like most automotive EFI). They are continuous flow and have pressure/flow when under pressure (boost pump on) even if the engine is not running. This is the idle condition. A trickle can add up pretty quickly.

Knowledge leads to improved safety!
 
When I was trying to start my engine for the first time, I had no idea how much throttle and mixture to give it. After a lot of unsuccessful cranking and horsing around with throttle/mixture, I pushed the plane back in to check other vital signs. Once in the hangar, I found 1" of raw fuel in the intake snout ... the liquid line was visible thru the fiberglass. Only then did I learn how much fuel a Silverhawk will dump when set full rich. That's why they flood so easy.... especially when hot.
 
During my fuel systems tests before Phase 1, I learned (by direct measurement) that the RSA-5 servo will flow 5 to 6 gallons per hour at the conditions noted by the OP.
 
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