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Old 05-05-2009, 09:56 PM   #29
Beastly Adventurer
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Joined: Aug 2005
Location: Belgrave, Victoria, Australia
Oddometer: 5,833
Originally Posted by sp4ce
Yep. Check and replace the filters before you drop $$$ on the pump.

I had all the symptoms reported in this thread - bogging at speed when throttle applied, intermittent poor running, turning the bike off and back on temporarily fixing the problem - and it was dirty filters. I replaced them and the bike was fine.
I worked for Bosch as a technical sales rep for 7 years so have had a fair exposure to fuel pump issues.

This is starting to sound like a pump cavitation issue.
I have yet to open mine up and see how it is all set up, but from what I can tell, the pump sucks in fuel via a sock filter, pumps it through a small fine filter, builds up pressure in some internal pressure regulator with the excess bled back into the tank and the pressure fed out the single line.

If I am correct in those assumptions then....
  • The same fuel will be circulated around the fuel pump in a very small volume as the tank empties out.
  • The tank is plastic so does not get rid of heat well.
  • The rather small main pressure filter will tend to block up quite easy, requiring more effort to pump fuel through, this will tend to increase the fuel pump power effort and hence heat generated.
  • Warm fuel being sucked through a partially pick up blocked filter will tend to cause the pump to cavitate, create vapor locks and generally conspire to stop the pump being able to create the pressure needed to run the bike. (EFI pumps are useless at sucking, great at blowing)
  • As the fuel temp increases the problem gets worse until engine stops altogether.
For those that have had the problem, does the 'tone' of the pump sound at all like it is sucking air when things start to go kaput?

Does this sound like it fits the symptoms?
Add fuel or let it cool and all is fine.
Cold ambient temps and all is fine.
Hot ambient temps and it all happens faster.
Traffic, where radiator heat is soaked into fuel tank, all is worse.
Freeways, more airflow throught radiator so less absorbed into tank, runs better.

Get the idea?
You only need two tools in life: WD-40 and Duct Tape.
If it doesn't move and should use the WD-40, if it moves and shouldn't, use the Duct Tape.

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