Mailing List flyrotary@lancaironline.net Message #13230
From: Russell Duffy <13brv3@bellsouth.net>
Subject: RE: [FlyRotary] Re: Bubbles in fuel line from pump - new valve
Date: Sun, 28 Nov 2004 11:38:50 -0600
To: 'Rotary motors in aircraft' <flyrotary@lancaironline.net>
Message
For a moment, let's assume that all your work on the fuel lines has proven that there's really no leak, or problems.  How about the carbs?  Is there a chance you have a needle/seat that's sticking partly open.  Is there a chance that the fuel level in the bowls is getting off level enough that it's causing problems?  Just looking for another possibility.
I'm not sure I follow this. 
 
 
My thought is that we've all fixated on the bubbles as the cause of your troubles, but some bubbles shouldn't be a problem assuming you have "standard" carbs with fuel bowls, floats, etc.  Bubbles flowing into a fuel bowl should just get vented right out as fuel behind the bubble takes it's place.   If you have too many bubbles, eventually the fuel level in the bowl will go down, and your mixture will lean out.   Do you have a mixture gauge?  Can you tell if the mixture is going lean, or is it going rich?
 
If you had a needle/seat that was sticking open at times, you would have lower fuel pressure, and you would eventually overflow the bowl causing your mixture to go rich.  I believe you said your carbs were vented to the intake, so the overflow would (mercifully) be ingested by the engine, causing the mixture to be even more rich.  As we know, the rotary can run pretty darn well at high power on a very rich mixture, so this may not be as obvious as you'd think.  How about the times you say you reduced throttle coming into the pattern and the engine quit?  
 
As for the carbs at climb attitude, carb bowls and floats are meant to stay level (within reason).  Tilting these to any extreme will cause an apparent change in mixture.  In the extreme, a float might stick open due to friction caused by side loads on the float pivot at climb attitude.  
 
Basically, I'm just trying to give you something else to think about.  A leak in a fuel line, pump, valve, etc, was certainly the leading possibility, but as many times as you've changed and re-arranged these items, I'm thinking they've been all but ruled out.  
 
One final thought- can you run on the center carb, and turn off the pump for the outer carbs? 
 
Gotta go,
Rusty
 
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