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Fuel pump vs gravity fed?
#1
After wanting an ultralight helicopter for decades I've gotten a Mosquito Air with a Rotec 503 / dual Bing 54's.  Question... I've seen videos & pics of BOTH pump (and gravity) feeding fuel to the carbs. And I've seen gravity ALONE feeding fuel to the carbs.  Whats the latest on this? Is there a relationship to this choice and the "notorious" Rotec engine stoppage I've heard about??
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#2
Fuel pumps were made safety of flight mandatory on all models early on after we found fuel starvation issues under high demand, eg take off, climb out,
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#3
Mandatory...Got'cha.  I wondered if pump failure was causing the engine outage's and so some went to gravity feed.  But fuel starvation and subsequent high temps and engine seizure...I see.  My used craft came without, but a new Mikuni pump is in hand and going on with the new fuel lines. Thank you
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#4
(12-28-2019, 05:31 AM)SkyFanDan Wrote: Mandatory...Got'cha.  I wondered if pump failure was causing the engine outage's and so some went to gravity feed.  But fuel starvation and subsequent high temps and engine seizure...I see.  My used craft came without, but a new Mikuni pump is in hand and going on with the new fuel lines. Thank you
The reason the Bing 54 carbs starved out on gravity is that the Bings supplied with the 202 were initially used in fixed wing ultra-lites where the fuel tank was most likely positioned  level or below the engine and a pump was needed. A carb set up for pump use will not work on gravity because the NEEDLE SEAT has a much smaller hole, so gravity can not supply enough fuel thru the pump needle seat when more fuel is required. Thus starvation. For gravity use a needle seat with a larger hole is needed.  

Hope this helps, leo...
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#5
OK...That makes perfect sense. This forum is turning out to be great. I'd read somewhere that the Bing 54 needed between 3 and 9 psi fuel feed. But that was probably for the smaller needle seat?? I did the math with density of gasoline per inches of column and it comes out less than 1 psi with gravity feed. That kind'a worried me. I've only peeked into the bowls when I drained the system. But I will KNOW what I got! Thank you very much. ...Dan
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#6
(12-31-2019, 07:04 PM)SkyFanDan Wrote: OK...That makes perfect sense.  This forum is turning out to be great.  I'd read somewhere that the Bing 54 needed between 3 and 9 psi fuel feed. But that was probably for the smaller needle seat??  I did the math with density of gasoline per inches of column and it comes out less than 1 psi with gravity feed. That kind'a worried me. I've only peeked into the bowls when I drained the system.  But I will KNOW what I got!  Thank you very much.  ...Dan
If your in need of a new pump I have one for $20.00 plus shipping costs from Wisconsin
Jim
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#7
That IS a better price than I paid. Question... IF I have the needle seat with the larger orifice (I haven't checked yet) - I could still feed  with a pump too - don't you think??
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#8
(01-01-2020, 06:58 PM)SkyFanDan Wrote: That IS a better price than I paid. Question... IF I have the needle seat with the larger orifice (I haven't checked yet) - I could still feed  with a pump too - don't you think??
Hi Dan

Of nine years of flying my XEL, Six of those last years I flew with 38 mm MikunI carbs. Never ran so good, mainly because it was now jetted  properly, from the pilot jet, to the needle jet ,to the jet needle, the slide & main jet. Not sure if theses numbers are correct but I have notes from  Bing Agency International L.L.C. and I have written down PUMP NEEDLE SEAT 1.5 & GRAVITY 3.7. Also noted PRESSED IN. Back to your question.  My answer would be NO!! I am thinking that a pump added to a carb that is set up for gravity ( larger orifice) would blow the needle off the seat. Here is where you can get some answers.

Bing International L.L.C.
1704 South 525 Road, Council Grove, KS 66846
Tech 620-767-7844  Toll free  1-800-309-2464
email: admin@bingings.com
Theses notes are from 2009 so things may have changed.
Hopes this helps "HAPPY NEW YEAR TO EVERY BODY'

leo...
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