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Can only Get 4GPH from Fuel Servo ??

laserman

Active Member
Having an issues with fuel low flow thru fuel servo...


Background...

Fuel Servo..

Model: AVX-5VA1
Serial # AV031425
Part List # AVX3015002-1

Mounted on
Lycoming YIO-360-M1B
Serial # EL-36699-F1
Shipped 12/21/15

Just finished up an RV8 and after proper flushing of fuel lines connected the AVSTAR fuel servo verify fuel flow rates...

With ample fuel flow and pressure being supplied from an ANAIR PX375-TC#3 (Rated at 16GPH @ 28PSI.. verified pressure and flow at the input port of the fuel servo... I’m only able to get 4GPH from the output fuel servo port at Full throttle & Full rich.

I have verified an absolutely pristine clean fuel servo input filter.. and no restriction of the input / output fuel servo ports... The fuel servo throttle and richness control has been verified by AP as correct and operate in a normal manner.. (Mixture control to lean stops fuel flow.. Mixture set to rich does give me 4GPH at full throttle)

In addition .. Engine idles and runs great till its demand exceeds 4GPH and the engine begins to stumbles due to lack of fuel flow...

So??? What do you think? Anyone else ever seen this issue ?? A simple suggested fix here? or is it a going to be a fuel servo exchange ?

Thanks
 
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airflow?

Not sure about the servo you have - I recommend you call the supplier. I recall reading that some systems require airflow inside the servo to change the amount of fuel that's sent up to the flow divider.
 
Feedback

Ya.. So have air flow thru fuel servo..... Engine runs great at fast idle.. So there is air flow... ???? Thinking.....

BUT your comments on air flow was the hint I needed... I opened up the emergency air source and



THE ENGINE RUNS GREAT !!!!!.



PLUGGED air filter.. !!! *)()(*)*)*)( Always something simple....

From the 5 years the filter sat installed... Getting lightly covered with sandings and paint overspray.. over and over...

(Yes I had sealed the engine fuel servo from the start... Knowing dust would be all over the place...)


ACtC-3dx-EW0bCekFRlPPhnQwubLlIE3APYlwKB657sf0F4xLUlRhzxiOGuNqOXdo5UulgyGcSTFcynMYxlk8BFGx05aRB-OAwL2k3tKX-xSjoNsMqt4bLUnB2z8FsQxCzZJd3FP1ZNX3z8ZYqSnxXN_iPQI=w1150-h862

AL

See you made the EGGENFELLNER SUBARU "WOOPS :>" early on as well... (So did I..)


Yep.. Been there.. did that :>..... 50 GPH to fuel servo... no pressure.. electric pump rated at MIN... 16GPH @ 28PSI... Darn dirty air filter. !!!


Aux Electric Fuel Pump...

ACtC-3fUzjwxSz0cPwLtMhECQs06FTDibLVhWaCtne4cYccDwsxObhBX2qm39ZjxJ2iqCRPZDrutGkHkb-47o6vGAbOTckaqYVW7oLeFXUtUenA0zRtyDZaZQTBQCcHmoHLzaMOk01L9C2-OgqNHYAxTvJRR=w1006-h754




VZqOYdkQNAFT9mIW_LYsnhQm2PqE8Gv7RaLShrqa9Wl5OZDZ-GjTSw0BUvKOzV_D4vBnEpbs1fxrr8Pe8xI-UdeIOOglx4YgkmUDf09RSXoQ7JqYYCWUb-sKvoWadOimaVzrZwdRv9f-pVX7jDc3_mdE4r6Vz7-E1SvN4HkOjRLRi_PZYIed1RGpfro7O6ZMmGIr9Yr2oTFtXns3Ef0sArt10UxZnowKuUQzhHT3DCWJATwONg1r6_QF2dXDXAdRXFU4zXcLEWcRyyuJpLNAezALsJtFMS1JyaFV3XWp21ulxfI5Aat-l-UCyPQ_jfcR6PL4zeepDLb6Ue9n99HeLPyy5MEP7XW0aEqzlyGsf_32FpMd04viTRTwzjZHezJfKUJMf3CxR1GZ_IEfo1Dtw7tSeucZMrN0r4-uzz9zmTGNS26N_yJ1omA5YFIk9P4Pyq4IRwPQdnWLGUXvU5_40DFQdarYRdY88tmly0dyxerbc3f-E9Pw4k5ylWQLsutK8ZpJpTMCovvWTxApFORgYGb5Q2CaTSAoYfvipD3hbEDecHER9B0p5t_XEsJT1qJW_HUWUo9gkGvP-QwZhFyKOuwqT9IybB2sf5SUAppnSYTQ8izIceRzoqC4HqIySKgRFoiEgn69UnjlT2X2JEWyNMH8pzGu8yhhF45Nx-bKAVTWsgeyB8FLuN1TwcSniw=w1119-h839




NOW I UNDERSTAND WHY THERE IS AN EMERGENCY AIR SOURCE FOR THE ENGINE.. !!!!!

AND IMPORTANTLY... KNOW THAT AN AIR FILTER CAN BECOME CLOGGED... EVEN IF IT LOOKS FINE !!!




AL...
 
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For my IO-360-M1B I wanted at least 30 GPH at the servo inlet. My AFP flows almost 60 GPH to the servo. If I may, what is your measured flow at the servo inlet (timed into a container)?

dave
 
The servo measures air flow through the throat and meters fuel flow out appropriately. I would not expect more than a few GPH on the output side with no airflow though the throat. Not sure what you are trying to test here. The std fuel flow test to prove your delivery system should be measured pre-servo.

Larry
 
Its the unexpected " Dirty Filter" that the real surprise... Fuel test at output of servo was only done because could not get engine above fast idle.. Because the filter did not "Look" to be dirty/plugged but it was... Look for the little things...

Chalk it up to first time builder.. and AP scratching his head...

But its all fun.. No Harm.. No foul... and learned a lot about the fuel servo.. So its all good...
 
K&N filters

Its the unexpected " Dirty Filter" that the real surprise...
Thanks for the update. I'm not exactly the biggest fan of K&N filters, but I have not found anything better for this application (yet).
 
Change it

Why not change the oil filter once a year at annual time. Such a cheap maintenance item ...
I assume you mean air filter, and I agree - I'll just change it every annual. It's about $50. Still don't like them!
 
What Larry said: The diaphragms in the servo measure pressure in the servo venturi, that in turn sets the amount of fuel the main jet will flow. It's for raw mixture adjustments for pressure. If you're not getting lots of air flowing down the hole you will not flow much fuel. The more air the more fuel..
 
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