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--- fuel_systems:fuel_pump_and_carburettor [2017/05/23 11:12] – created sb66
+++ fuel_systems:fuel_pump_and_carburettor [2017/05/23 14:18] (current) – sb66
@@ Line 45: / Line 45: @@
   * Replace the contact set. One is available from Wemoto   (external link)
   * Replace the pump. There are various different pumps which can be used in addition to the Honda version, they are less expensive and allegedly more reliable. Pumps made by Mitsubishi, Quinton Hazell (QFP171E1), Facet  (external link) and others have been used. Here is an edited version of an installation report for a HUCO 133000 pump.
+My original pump failed last week, in the middle of Penzance. I was a bit surprised as I'd modified it in good time to reduce contact arcing, however, it turns out that the contacts were fine and the fault was a mechanical one whereby the contacts were left permanently open, unclosed by the return spring.
+I fitted the handy bypass tube by the roadside, a job made less easy by the installed crash bars, filled up with petrol and rode home.
+Next day I fitted the HUCO 133000 pump using the original rubber holder. I oriented the pump to ensure the legend 'TOP' was indeed at the top and moved the adjustable inlet and outlet stubs accordingly. Although the 8mm pump stubs were smaller than the original 10mm tubing two of Commander Robinsons' excellent jubilee clips took up the difference. This was aided by the necessity of cutting back a small amount of original pipe giving the tubes fresh un-distended ends.
+Here are the photos :
+{{:fuel_systems:hucco_pump_end_view_copy_.jpg?200|}}  {{:fuel_systems:hucco_pump_from_below_copy_.jpg?200|}}
+ {{:fuel_systems:hucco_pump_from_front_copy_.jpg?200|}}  {{:fuel_systems:hucco_pump_side_view_copy_.jpg?200|}}
+ {{:fuel_systems:pump_connector_location_copy_.jpg?200|}}
+==== Prophylactics, or what you should have done before it failed. ====
+To stop the contacts from burning out some attempt can be made to reduce the contact arcing. This can be done by
+  * Routing the solenoid current through an electromechanical relay switched by the pump contacts. This moves the arcing from the pump to the relay, which is not usually designed to handle this level of duty. It's probable that the result will be the burning out of the relay contacts, but the relay may be cheaper or easier to change than the pump and it has been done.
+  * Routing the solenoid current through a solid state switch, eg a Bipolar or FET or SCR. A suitably rugged device can be incorporated into the pump casing and has been shown to work.
+  * Placement of a capacitor across the points to damp out the spark. This has been claimed to work, the capacitor value would need to be sufficient to reduce the arc but not slow down the pump and the capacitor rating sufficient to withstand the high voltages encountered.
+  * Shunt the arcing current by a silicon diode across the solenoid. An edited report of a diode installation is shown below.
+  *
+Note: all these solutions require modification to the internal pump wiring.
+==== Purpose and Operation ====
+The Varadero has a fuel pump because the fuel level drops below that sufficient for gravity to feed petrol to the carburettors. Similar bikes with different tank arrangements don't require one, eg the VTR1000F Firestorm. The location and quality of the pump suggests a stop-gap measure by designers thinking ahead to a fuel injected bike. This type of pump has been used in automobiles for at least 60 years and has always had the contact wear problem. The diagram of the pump below is actually of a c1970 S.U. car pump.
+The pump delivers fuel to the engine as and when the engine requires it. Functionally it is a solenoid driven diaphragm that's controlled by a demand valve.
+Assume fuel is available at the inlet of the pump, connected to both fuel taps. The carburettor float chambers are not full and the engine is not running. Operation is as follows:
+{{:fuel_systems:fuel_pump_diagram.jpg|}}
+  * The diaphragm is at rest and held by the spring towards the valves, the pumping chamber at its minimum volume. The contacts are made but not connected to the supply.
+  * The engine is started, ignition pulses are sent from the ICU to the ignition coils and to the fuel cut-off relay. This triggers the relay which holds on long enough for succeeding pulses to maintain it constantly energised. This ensures that the pump stops if the engine stops in case the fuel lines are damaged.
+  * With the relay now on a 12v supply is available at the pump.
+  * Current now flows through the contacts, energising the solenoid, drawing in the armature. The attached diaphragm moves enlarging the pumping chamber and drawing in petrol via the pump inlet valve.
+  * As the armature reaches the end of its stroke the contacts are forced open by the rod and rocker arrangement attached to the armature. The solenoid demagnetises and the spring propels the armature and diaphragm to its resting position, thus expelling petrol through the delivery valve to the carburettors. The contacts are remade to restart the cycle. The mechanical arrangement of the contact mechanism and inertia of the moving components ensure a sufficient throw of the diaphragm to pump effectively.
+  * This cycle continues until the carburettor float chambers are full when the float valves close off the flow from the pump. On the next return stroke the diaphragm is unable to empty the pumping chamber and stops moving with the contacts open, stopping pump operation. As the petrol is used in the engine the float valves open and pumping continues.
+The usual, though not universal mode of pump failure is erosion of the pump contact points to such an extent that they no longer make a reliable switch. This is due to the constant arcing of the contacts on each episode of contact separation, caused by the energy in the rapidly collapsing magnetic field around the solenoid discharging across the air gap at the points. Modifications to reduce this arcing are an attempt to divert this energy away from the contacts through a lower resistance path.
+Created by JP on the UK Varadero forum - copied to this Wiki by SB on 23/05/17.