# Walbro Fuel Pumps

### Help Support HomeBuiltAirplanes.com:

#### TXFlyGuy

##### Well-Known Member
We discovered why the CB’s tripped...the filter was so plugged up the pump could not work.

#### akwrencher

##### Well-Known Member
HBA Supporter
Well that's a good thing to get sorted out on the ground. Glad you found the smoking gun. Always a good feeling.

#### Jay Kempf

##### Curmudgeon in Training (CIT)
Did someone say filter and restriction?

#### FinnFlyer

##### Member
After Taxi tests. So when engine is idling for a while? If the fuel pressure regulator has excessive restrictions in the return path to the tank the pump may work a lot harder than when engine is using power. I would hook up an ampmeter is series with the pump and watch the current under various engine power conditions. Also try in series with the other pump for comparison purposes.

If you don't have a multimeter or amp meter that can handle 10+ amps, put a 0.1 ohm (or even 1 ohm) resistor in series instead and measure voltage across the resistor with a multimeter (voltmeter). Current = Voltage / Resistance (Amps = Volts / 0.1 or Volts / 1).

Finn

#### FinnFlyer

##### Member
Sorry, didn't read the second page.

Finn

#### Bobby Hughes

##### New Member
Well after start up. During taxi tests. Or just after extensive taxi tests are over. It pops. Engine real quiet.
Initial start up is just fine.

Where is a good source for USA made Walbro pumps? Summit charges around $250, everyone else charges around$110-\$120.

What is the battery voltage after disconnecting the alternator? I flew for 500+ hours with Walbro pumps feed with 10A breakers and didn't experience any issues. I would see 6A at 48PSI. About 6 ft of 14G wire with return wired to a ground buss and not the airframe. I always ran both pumps for takeoff and landing. Each pump had a slightly different sound and one pump had some electrical noise. That pump was not on a breaker but on a polyfuse. It's really odd that the breaker trips after shutdown. I would suspect a high resistance connection. I've seen inrush current damage fuses that would hold for 2-3 power cycles.

#### Chris Matheny

##### Well-Known Member
HBA Supporter
Plugged with what though? Shavings from a failing pump? I'd be looking for the cause of the shavings.

#### TXFlyGuy

##### Well-Known Member
Plugged with what though? Shavings from a failing pump? I'd be looking for the cause of the shavings.
Clean filter

Dirty filter

#### Chris Matheny

##### Well-Known Member
HBA Supporter
Looks like a 40 micron pre-filter like I use on small engines. I prefer a lot more surface area on anything making much over 100hp.

#### TXFlyGuy

##### Well-Known Member
These are from Jegs. In line filters. Washable.

#### Chris Matheny

##### Well-Known Member
HBA Supporter
Same ones. Summit sells their version also. Just not enough surface area for my liking. I use the reusable log filters from speedway motors for any big HP engine.

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#### proppastie

##### Well-Known Member
Log Member
Might do a flow test

#### rv7charlie

##### Well-Known Member
Tx, I don't want to be rude, but some things just need to be said. For safety's sake, y'all need to do a serious safety stand down before getting anywhere near flying. I wouldn't run that filter on a Briggs V-twin in an airplane. Like Chris says, there's just not enough surface area. That could have happened on takeoff, and if the other pump has the same style filter, even the combined area could get clogged by minimal trash in the fuel system. I'd be paranoid about it having enough area to avoid vapor lock on the pump inlet, even with perfectly clean fuel, given the HP & fuel flow that engine is capable of. For your HP engine, I's expect the fuel line itself to have that much area. Compare its surface area to something like this:
intended for significantly lower HP engines.

I know it isn't pleasant to hear, and I hope that you realize we're not just trying to 'pile on' in criticism, but that filter, and one of your earlier posts showing a reduction drive oil line made of clear plastic tubing, really is scary. Please...read this post in the context of serious concern about what looks to be a really nice plane (and more importantly, pilots).

Charlie

#### TXFlyGuy

##### Well-Known Member
Thanks for the suggestions.

#### skydawg

##### Well-Known Member
I’m familiar with the LS series Waldron pumps (now TI automotive). i would suggest putting an amp meter on each without engine running and log start up load and every 1 minute thereafter for the amount of time you normally see the breaker pop. Compare each Pump.

fuel pumps amp loads vary with system pressure, the higher the pressure, the higher the restriction and amps. not knowing what pump model, I would expect you will see about 6.5-7 amps each. Also, if breaker pops again and amp meter reads normal, breaker may be bad or too low a rating, 20A is recommended for most 12v models. If that doesn’t indicate anything wrong, now repeat but with engine running so alternator is increasing voltage. The pump pressure and volume increase with voltage, so pump will function different with 14 volts than 12. If you see amp loads increase more than a couple of amps, than pump motor or connections are likely issue.

one last thing to check is a contaminated ground circuit. check for no or minimal voltage on the pump ground terminal. poor ground can cause pump to overheat and draw more power than normal. Then check For voltage between positive wire and battery + terminal, there should not be any.

one more thing once you figure it out, Most Waldro Pumps have open terminals. I’d recommend using something like liquid electric tape to cover them and prevent corrosion and accidental shorting. if the pump fails while engine is hot, it may likely be vapor lock....typically pump makes a squeaking whine as the impeller cavitates. It doesn’t take much temperate, especially with ethanol gas.

hope this helps. Good luck.

#### TXFlyGuy

##### Well-Known Member
Airflow Performance filters ordered. A set of two, 40 micron.

#### TXFlyGuy

##### Well-Known Member
When I went to look for AFP filters, I found this related commentary about the filter problem and the AFP solution: Another AirFlow Performance Fuel Injecton emergency,
The new filters are large, 6" in length, and 1.5" width. Plenty of surface area, unlike the disc that I am replacing.
I have a 90 micron filter between the center header tank and and the pumps.

Only one pump is run during flight, with the other pump in a standby capacity. If one filter were to clog up, the immediate action item is simply to select the standby pump. This happens automatically with the EFII Bus Manager.

#### skydawg

##### Well-Known Member
I would further suggest redundant pressure regulator on each pump. For the c172 system there is 3 ways to activate backup pump, including an automatic mechanical switch on fuel rail that doesn't need any electronics and a warning light in cockpit to let you know it was activated. This level of redundancy was to meet FAA cert requirements and likely excessive for experimental, but it is a simple 3rd layer.