David Jenkins
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| posted on 7/6/08 at 11:44 AM |
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What am I doing wrong with my bike fuel pump?
I have just fitted an ex-ZZR1100 fuel pump in place of a Facet pump. It's mounted just in front of the rear axle at the level of the bottom of
the fuel tank.
There's a length of 8mm pipe between the pump and the engine compartment, and it has to lift the fuel about 35cm to the carbs. The
filter/regulator has been replaced by a large disposable in-line filter about 10cm before the carbs.
The problem is that the pump is rapidly filling the tube, then half of the filter, then it stops. I would have expected it to fill the filter and
then the carb float chambers.
It's not a fuel pipe blockage, as it used to function very well with the facet pump and filter/regulator when feeding the old Weber DGV carb.
However, that system didn't feed the bike carbs very well, hence the change.
Any bright ideas?
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worX
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| posted on 7/6/08 at 11:50 AM |
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There is no pressure drop filling the filter so it is a possibility that it is filling the float bowls with only half the filter full.
Do you have problems in starting/driving it?
Just because the facet pump pumped through the line correctly doesn't necessarily mean that the fuel line is now perfect for the bike pump.
I'm not saying there's anything wrong with it, but to discount it without testing could be a PITA later perhaps?
Just in case it's the filter (surely not, but you never know) I now use one of
THESE.
HTH
Steve
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russbost
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| posted on 7/6/08 at 11:53 AM |
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IIRC the ZZR 1100 pump cuts off at about 3-4psi it could be that the weight of fuel above the pump is enough to generate this cut off pressure, try
raising the pump, I don't think there is any similar problem on the suction side of things if you follow me. HTH
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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MikeRJ
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| posted on 7/6/08 at 12:13 PM |
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A 35cm head of petrol will generate a pressure of under 0.4 PSI, so that shouldn't be a problem.
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David Jenkins
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| posted on 7/6/08 at 12:44 PM |
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It's still peeing down with rain outside, so I haven't had a chance to roll the car out and crank it over... 
Mike - useful info about the pressure resulting from a 35cm head - I'd considered the same issue as Russbost, so it's nice to know that
it's unlikely.
Steve - the filter's on a 45-degree tilt, and it's only filling the lower half. I have a spare filter just the same as the one fitted,
and I can blow through that one with very little resistance.
What really pees me off is that the Weber DGV works pretty well - but is a pig to tune up properly, refuses to tick over nicely, and stinks of petrol
every time I stop. I really want to get these bike carbs working as they're so much more usable in almost every respect. They look and
sound better too! 
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owelly
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| posted on 7/6/08 at 12:58 PM |
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If ther float bowl is full, the needle valve will have closed and the pipe may be full of air.
You don't say if you have run the engine. That would empty the float bowl, drop the float and let the fuel through.
Have you tried pulling the pipe off the carb and looking to see if the fuel comes out? I have a disposable fuel filter on my car and it only ever
fills half full but that is because there is a little tube that runs up inside the middle of the filter that creates an air lock. The filter still
works and the fuel still gushes through at an alarming rate!!
http://www.ppcmag.co.uk
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David Jenkins
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| posted on 7/6/08 at 01:04 PM |
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Fair comment - I wish it would stop raining, so I could give it a try...
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rusty nuts
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| posted on 7/6/08 at 01:10 PM |
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It's quite common for fuel filters to not fill completely . If you have any doubts as to whether the pump is working correctly as Owelly
suggests disconnect the delivery hose and check fuel flow or start the engine?
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richmars
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| posted on 7/6/08 at 01:53 PM |
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Agree about the 0.4 psi from the head of fuel, but you also have a pressure drop across the filter. When running, there will be a pressure drop across
the filter, like a voltage drop across a resistor.
The pressure drop should be detailed in the filter spec somewhere.
You could put the filter before the pump and see if that works. (That's what I do with my Fireblade.)
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GaryM
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| posted on 7/6/08 at 01:57 PM |
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My cheap clear fuel filter is at a similar angle and only half fills. I guess the trapped air has nowhere to go so stops the filter filling
completely, the car still runs OK.
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David Jenkins
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| posted on 7/6/08 at 08:26 PM |
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Looks like you chappies might be right - the rain finally stopped at 8:00 this evening, so I pushed the car out and started it up. It ticked over for
5 minutes or so, so fuel is obviously getting through.
If the weather forecast for tomorrow is OK then I might get out and give it a blast - but there are some MAJOR puddles out there!
Will it ever stop raining?
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