Schematic
By:rideswestKTM
I really wanted to do this right for OC but yet again I failed to get good pic's. But I thought I'd post anyway -better something than nothing.
This is a mod to perform on the 950 KTM fuel pump (other bikes too) that should make the pump last foreve...a long time.
Parts are less than $5. The way this mod works it is IDENTICAL to stock - the difference is the points act as a trigger for the solid state switch instead of being the switch. So stock current through the points is 6 amps, and with this kit, it is down to around 1 miliamp.
Need two resisters (may be really small in size) 1 megohm and one 15kohm, I have also used 10k for the 15K, makes no difference. You need one MOSFET I used a IRFZ44 (radioshack # RSU 11467040) others may work but - I look for good current rating (>10) the above is like 70, and the terms "gate", "drain", "source". Also need a small screw (like 4-40 x 3/4"long or longer.) plus two nuts. A 3mm terminal lug is good too.
FET prep: Looking at the FET from the front leads down (front has step). The left one is "gate" center is "Drain" and right is "Source". Bend the center one away then back to parallel with about a .1" offset. Bend the Gate outward and the Source outward. Put the screw in from the backside and put one nut on it to bind on the FET (this keeps the screw in place but also (check this use a washer if necessary) the nut is level with the FET front. Using short leads solder the 1 meg across the Gate and the Source, not touching the bent-down center wire. The resistor needs to be nearly level with the front of the FET (that's why we bent it down.)
Pump mod: remove the cap -push in the wires as you remove. Unsolder the point wire from the top of the point assembly.
Remove the ground wire connector. Solder the 10 to 15k ohm to a connector lug and put it where the ground wire was. (note if you put the screw in without a lug or a washer you can damage the coil - may still work but don't do it.) As you tighten the screw try to keep the resistor out of the way. It took me a few trys even after soldering the FET to do this.
Shorten the FET leads as you go with the following steps. With the point wire unsoldered, the hole from which it came, can be cleared enough that the FET Gate wire can be pushed into it, melt the solder if not. The screw will be pointing away from the body towards the cap. Solder this joint with about .15" between the FET and the point attachment lug.
Use shrink tube if you got it on the coil wire. Solder the coil wire to the center "drain" lead. Insulate (shrink or tape) where it crosses the point bridge.
Strip a small spot or poke a hole in the insulation of the positive (blue/black) wire around .5" to .75" from the pump body. Solder the 10-15K resistor into this spot. Insulate - I used RTV.
Cut the ground wire so it will attach to the source lead without tugging or pushing on the FET, and solder.
Measure the distance from the cap holddown screw (put the screw in a little ways and measure from the screw cross) to the screw in the FET. Measure this distance on the cap from the screw hole to where the FET screw will come thru the cap. Estimate distance from edge of cap close is good enough. Drill an 1/8" hole in the cap at this point.
Hint: push the wire feedthru plug away from the pump and then you can pull it into place. Silicone grease is good to help seal, there and around cap o-ring. Work the cap into place helping the screw to go thru the new cap hole. Once in place RTV the hole and screw put the nut on (washer would be good too -forgot to mention) nut it. Once RTV is dried (or sooner) cut off excess of screw if you want - I held the screw in the vice and cut with hacksaw while holding pump so not to wiggle the FET. More RTV to ensure sealing.
KOTH:The following images are by fmfpunk and may help you visualize what is being discussed:
Schematic
Stock Pump's points actuated mechanism
Solid state actuation device installed