Fuel pump cavitating.

[GARRICK.CLARK]

Hi Guys.
My fuel pump is making an whining noise, like its running out of petrol.
Is this Cavitation.
Its made my motor show lean on the AFR gauge,
Pump is a low miles bosch unit
How do I go about fixing it.
I'm using the CB tank fitting which has fuel return to the bottom the tank, fuel line to the carbs ,and fuel line back to tank are both 8mm.
I have a 13mm hose from the tank to a filter then to the fuel pump inlet.
I have read not to fit a filter before the pump as its a restrictor and gets more restricted as the filter gets filled with any dirt.
So what should I do to get my pump from cavitating and to get a less erratic sounding pump.

[saltgrinder]

Was the filter blocked with crap ? I use an aeromotive brass filter in front of my Bosch pump made for this exact application

Richard

[Piledriver]

EXACTLY which Bosch unit?

If its a roller cell pump like a -044 it really, REALLY prefers a feeder pump/mini recirc sump setup.
It will PROBABLY cavitate without it, esp if its warm out.
Seriously.
If it was out of late MK1 or MK2-3 VW it originally would have had that setup attached.

Also, don't ditch the check valve on the outlet, the pump works much better and it is flow/pressure rated with it in place.
Bosch roller cell pumps are flow rated at 90 PSI, rather than with zero backpressure (open hose) like most others.

[GARRICK.CLARK]

I dont have the exact bosch number to hand at the moment. Its got good psi and flow, think its 70 psi.
So it could be the pre filter full getting blocked. I'll check that. May even take it off to test it.
So its not the CB tank out let then.

Engine went lean as I got on boost.
Fuel pressure gauge fluctuated at idle.
P.s Yesterday was the warmest day.

[Piledriver]

You need to find out the part number.
I'm not kidding on the roller cell pump, I got a smoking deal on a new ("bad") 044 pump because the PO didn't quite believe me when I told him the same thing. It was cavitating like crazy for him, set up ~exactly like yours.
Plugged it into my system with a feeder and sump and it has worked perfectly for years.
(The 30 year old junkyard pump I had been using that had outlived two cars finally died)

My "feeder" is a ~25 year old carter clacker with a bugpack sticker that was rattling around in my toolbox for years.
They can move a lot of fuel with no backpressure.

I'll merrily pay you $40 for your "bad" roller cell pump so you can buy a Walbro that doesn't need a feeder and sump to work...

[GARRICK.CLARK]

Hi Pile.
The pump is a 0 580 254 984.
I just don't get it . It was running fine. AFR was good, the carbs enriched to 11.5 at WOT. Went for another drive and it started going lean on boost, with backfiring. I didn't fiddle with it prior to the drive.
1 thing I did find was the rotor when fitted in the dizzy shaft is a tight (ish) fit but does have some side to side movement. dizzy is locked. I have another rotor that's a good solid fit.
I took out some unneeded hose length from the tank outlet to the pump. Fuel gushed out.(good flow).
I also took off both carb inlet pipes off the carbs and put them in a petrol can. Hit my prime button and watched the fuel go in. It flowed ok but not as I would have expected with a big pump pushing it through an 8mm pipe.

[GARRICK.CLARK]

So if I have this right I need to use another pump to push fuel into the main pump. That will stop it cavitating.

[GARRICK.CLARK]

hi guys so I went out for a spin in the car just now and it seems ok when it's cooler and has the car warms up and the pump warms up it just leaned out so I put the car back in the garage checked the fuel pressure gauge and it's fluctuates from 1.5 -3 PSI. Pumps fizzing away. Took tank out. Removed pre pump filter. That has some resistance when i blow through it.Not as free flowing As a piece of hose.

[Chip Birks]

Does your tank have a breather?

[Piledriver]

It needs a feeder to a recirculation sump with a return to tank to purge any vapor out of the system.
The regulator return is to the tank, the suction of the pump is at bottom of the tank.

I made one for my 914 from some 3" SS tube, the one in my square is from a VW Fox, but most any CIS-equipped mid-Mk1>3 has what you need right by the pump.
(early MK1 golfs had the pump suck right on the back of the tank with a huge hose--- It almost works)

Fuel can get ~20-30F over ambient easily as it circulates, and its boiling point is seldom much over 100F, and it can easily cavitate on suction at far lower temps.

The only downside of a roller cell pump is that it doesn't suck.

[GARRICK.CLARK]

Yes, it has a breather. It is tiny. Its on the filler neck ( 67 bug ). Do they have to be a certain size with a turbo motor.

[Piledriver]

The concern is simply that it might be pulling a vacuum on the tank if it was sealed, happens sometimes, say if a wasp decided the end of that vent tube looked like an awesome place to build a nest.

...Evaporative control systems later cars have, the vent terminate in the air cleaner or TB, so its a non-issue.

[petew]

Is a tank breather a good idea on older cars updated with higher powered motors?

[Slow 1200]

if you run it with the gas cap off you will rule out any breather issues

[GARRICK.CLARK]

Yeh I'll try that. Nice 1