Walbro Pump Noise

[rjwoods77]

We thought we might have blown the pump in aour Wlabro PFA-32 with the noise it was making but realized there was a tank venting problem and it might have been "air-locked" or some shit like that. We got the pump flowing and it has a quite buzz to it when it is just free flowing. But it made this noise that sounds like a huge walbro pump in a race car. Is that what it sounds like when it is pressurizing fuel or is it our dumb mistake that caused it and it no longer makes the sound? We have to fix the tank still and havent had a a chance to see what the loaded pump noise would be if it matches the huge noise we heard before.

[rjwoods77]

We thought we might have blown the pump in aour Wlabro PFA-32 with the noise it was making but realized there was a tank venting problem and it might have been "air-locked" or some shit like that. We got the pump flowing and it has a quite buzz to it when it is just free flowing. But it made this noise that sounds like a huge walbro pump in a race car. Is that what it sounds like when it is pressurizing fuel or is it our dumb mistake that caused it and it no longer makes the sound? We have to fix the tank still and havent had a a chance to see what the loaded pump noise would be if it matches the huge noise we heard before.

[NetKev92]

I have a moderate to high capacity Walbro in my supercharged Miata that starts and stops buzzing as it pleases. The buzzing was fairly bad for a couple months but it's mostly quiet now and the buzzing is lower volume now even when it does happen. It's common enough that people in the miata.net Power Mods forum section talk about it from time to time. Several people suggest it's cavitation in the pump because an oversize pump is installed for the actual fuel flow rate. I don't know how to check and pin down the cause of the noise for certain, but the approach on the Power Mods forum was mostly to ignore the pump noise and listen to the boosted engine instead.

[billywight]

Our walbro pump was making random noises like that and during the endurance event last year at west it decided to crap out. We think it was because of particles in the fuel lines. Check your filter and possibly replace the pump - it's cheaper than not finishing endurance...

[rjwoods77]

Well we sorted out most of the issues except for one weird one. When you run the tank dry and the pump pulls a little air, you have to reverse the pump polarity for just a second before it starts pumping fuel again. We did it over and over. Run the fuel ou of the tank, fill it up and wait a couple minutes and nothing. Reverse the pump for one second then put it back correctly and it runs fine. This is all disconnected from the fuel rail. I do intend on getting another one asap but was just wondering until I get a new one.

[Chris Boyden]

cavitation occurs when the pump is trying to draw fuel but no fuel is available, which may point to a restrictive fuel filter on the suction side of the pump. You may consider a filter with a coarser element.

[Dan Deussen @ Weber Motor]

Rob,
are you running the Walbro Multipoint-pickups also in your car? If so, typcially there are two different types. One with and one without a bleed hole. Once the valve in both pickups have been drawn shut by the pump they will only reopen if one pickup with a bleedhole allows air to get back in the system and allow the valves to reoplen.

I am guessing you don't use a pickup with a bleed hole so by reversing the pump you push the valves back open.

[rjwoods77]

Dan,

We are using the MP-12 in the car right now that came with the kit. I just figured out what you were talking about by sucking on the MP-13. I dont remember seeing a bleedhole on the MP-12 and dont see one on the MP-13 even though testing it it seems to let go when you suck. Am I supposed to drill something out of one of those "ports" to make this happen? Use the MP-13 and not the MP-12?

[Dan Deussen @ Weber Motor]

Rob,

I don't recall which one exactly had the bleed function but if the MP-13 is the one that seems to release then use that part. I wouldn't recommend drilling anything on the MP-12!

Why do you only use one of them? They are meant to be mounted in each side of the tank so you can make sure you get fuel to the pump when cornering hard and the fuel level in the tank is low.

[rjwoods77]

Thanks Dan. Plumbed up both and it works good now. I love getting simple stuff pointed out. Being called dumb sure makes you learn quick. Hope things are all good with Weber. You guys going to get a twin together for FSAE?