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Fuel Pump Repair ( ST1100 ) *

Started by KoTAOW, April 04, 2012, 04:59:08 PM

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Contributed by John Hudson, aka GitSum, STOC #8086


Fuel Pump Repair ( ST1100 )

Here is how I was able to revive my OEM pump.

I originally took it apart to just see how it worked, but the only thing wrong with it that I could find was that it was
pretty well "crudded up"

First of all - this is what the armature and magnets looked like once I pulled it apart! Geez, I wonder why it stopped working!

I pulled the pump out of it's housing by removing the white nylon clip at the end.

I used my trusty Dremel® tool to slice the case open. I also had to pry up the tabs that fold down over the end piece. Not a whole lot you can damage unless you go really deep with the Dremel®.

Here are the pieces starting to come out (this is after I semi cleaned everything up and put the pieces back in place for the photo).

Here are all the parts cleaned and ready to go. The white circular piece (top left) is actually the front part of the pump chamber. The large hole with the slot is where fuel flows in an get pushed out the circular hole which has a little nozzle on it. Look at the brushes - this pump ran for 100,000 miles and there is still plenty of material left.

I put everything back and used that hose clamp to hold it together for now. I started sliding it back into the housing (it's actually a pretty tight fit) I just removed the hose clamp and slid it the rest of the way in. The slice in the casing didn't really seem to have any effect on the pump or it's performance.

Here is a better picture of the components with the armature and magnets removed. The black impeller goes inside the housing directly above it and the armature has two 'forks' that fit into the two slots of the impeller. The larger nozzle on the left is for 'fuel out'.

It is possible that the "guts" of the pump may slide out - but due to the wiring, I think it is going to have to all slide out in one direction. I really didn't expect to get the pump working again and the easiest way to take it apart was to cut it open. Actually, I don't think the cut really effects very much - the case may be just a hair bigger now but is contained by the housing. The armature rides in the synthetic end caps so it shouldn't be effected. I put a couple of thousand miles on it and ended up selling the bike.


Thank You again for your contribution John Hudson, aka GitSum, STOC #8086


Comments by Norm Keller, STOC#8030

The manual is not of much help for testing of many components, pump included. A pump diagnosis should include volume measurements, pressure test (dead head pressure) and current draw.

A good pump delivers delivers 1 liter in less than 35 seconds dead-head pressure 2 PSI and draws 0.9 amps. which was the comparison on which I based the theory or commutator issues.

A poorly performing pump is typically in the 0.7 amp range from a 12.5 volt source (a battery without running engine). IME, this is the most reliable test of a pump's condition providing that inlet and outlet are not restricted by something such as a plugged filter.

I recommend testing current by jumping the pump directly to battery power in order to measure outlet volume and current flow. This can be done with the pump in place and is part of my periodic PM testing, and something which might be considered by others in order to try to anticipate problems.

A subsequent test of pump current with the pump connected to the bike's wiring should indicate a similar current flow, otherwise there is excessive resistance in the bike's wiring/components.

Most of the pumps I have seen have not had significant commutator damage and have only required use of crocus cloth to clean the coating (appears to be a lacquer or varnish) from the contact surface of the brushes and commutator sections..

Rather than cutting the case as suggested by John, I pry the case tabs back to allow the end housing to be withdrawn. This allows the tabs to be pushed back into place during reassembly, this making the assembly appear as original. Which ever technique most appeals should be equally successful.

Inspect the pressure relief (by-pass) valve as sticking or material holding the valve open allows loss of pump output and reduces both volume & pressure while showing a normal current flow.

I continue to search for failed pumps as test mules and would appreciate contact with someone who has a poorly performing pump and would be willing to try some experiments. I would like to explore the removal of varnish/lacquer by use of some solvent such as Sea Foam® or, failing that type of product, a diluted lacquer thinner or other more aggressive material.

I have repaired several of these pumps as well as alternators, ABS Modulators and other components.

Good job on the post, John Hudson, aka GitSum, STOC #8086. It may be quite useful for someone needing to do this work.


Thank You for your contribution Norm Keller, STOC#8030