Yesterday I decided to run the fuel pumps to cycle some fuel through the engine. Both pumps bogged down and produced no pressure. After removing the pumps and much dinking around, I found both check valve poppets at the discharge end of the pumps were stuck shut and not allowing fuel flow. I swished them around in some Berryman's and gently pushed them open. The pumps seem to function ok now but I certainly didn't need this and it doesn't bolster my confidence in these units. Fuel is autogas non-ethanol with some 100LL added and as been sitting for about a month.. 

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If you decide to change out the pumps,  I have 3 available that I am not going to be using.  I changed my system out to a Viking header tank.  I have two pumps with less than 40 hrs on them and one that is completely new and unused.  No reasonable offer refused.  I have not checked with Zenith to see what they are worth.  I did not have any pump issues that caused me to switch to the Viking system.  Pumps don't work if you don't give them fuel to pump.....   Dr Fred

Thanks Fred, I'll keep it in mind. Still a long way from flying so I will use these for ground runs and decide about changes at a later date.  Tom

I have 400 hrs on my UL 350iS and have replaced both fuel pumps twice so far. I found that I am getting about 150 hrs out of them then they start losing pressure and acting erratic. Cheap insurance to just replace them in my opinion. If they fail in flight you've got a glider!

What is the brand of these pumps? Maybe you could use a different brand with similar flow characteristics, like a Walbro?

I see some on Amazon that look like these that are Bosch pumps. Maybe have to look into a different one.Thanks for the info..

Thank you for the good information, Jan. Your point is well taken.

I mentioned the issue now brought up by UL in their latest service bulletin over one year ago.  They are still playing fuel system catchup and the Band-Aid fix of creating a bleed around the regulator to allow the main pumps to re-prime in case of a vapor lock, is just that - a Band-Aid.  Or, in my opinion, criminal.  Their system has now been "corrected", after seeing my post.  The problem is that this knowledge is 10 years old and plenty of new info is available to stay safe, but still not implemented.  

For anyone with the same bad luck with fuel pump check valves as I have had, I found them on Amazon as Bosch p/n 1587010536. Twice now both valves have stuck shut at the  same time after a period of sitting idle.


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