Hi, just bought a Mk3 Superlight and noticed that the fuel pump runs contantly even before you start the engine, is this correct?
The fuel system isn't gravity feed, so it needs a pump running all the time - it has no facility for it to switch itself off when the float bowls are full, hence the return flow back to the tank - you should find a Y connector in the fuel hose roughly midway between tank and carbs. The fuel line pressure is around 3psi - 4psi max. If you want to stop the pump while checking electrics etc, insert a hidden on/off switch in the electrical supply to the pump - I had mine inside the left seat fairing, so I had to put my hand underneath to switch it. It would do about 1.25miles on full carbs with no pump running. In addition to what I said about it not being a gravity system - 1) if you brim the tank, put the bike on a rear paddock stand, fuel can eventually find it's way through the breather valve. 2) If you do the same with the bike on the sidestand or on a paddock stand, if the weather gets hot and the breather doesn't quickly let go any tank pressure, it can force its way past the carb float valves and pee out of the overflows - a siphonic action then starts and you could possibly lose a whole tankful.
Thanks could I ask a couple more questions, the battery light won't come on when the key is turned, bulb good, looks like its had a new rectifier with an extra bracket, also the fuel light won't come on bulb good and empty tank, guess I need a thermister
Can you get the make of the reg/rec? I think know what the problem probably is, particularly if it is an Electrex RR51 reg/rec. I'll post a pic to help you trace it - it is the white wire that sometimes doesn't get connected. Fuel level sensors stick - you fix them and a week later they stick again. Use the trip meter and fill up every 100 miles. Later sensors are more reliable (apparently) but as my 97 SS is 'late' and was always on, I couldn't be bothered to change it, so I used the 100 mile rule.
Not sure what make it is but its too big to fit in the frame where the original went so it has a bracket to drop it down, it has the white block connector and two yellow wires which I have soldered because somebody had used crimp connectors which were getting hot
Here's the RR51 set-up compared with the OEM one. Note the red/white wire in the bike harness - you should find the connector somewhere on the left side beween the headstock and headlight - maybe lower down at reg/rec level. Note both reg/recs have a white wire - they are the ones that make the charge light work.
Ok here's what i've found, from rectifier 2 red/white 2 green...from loom white plug 2 red and 2 black...found a staggered connector with 1 red/black and 1 red/white, when I feed power to the red/white the battery light is on
The staggered connector with the red/white in the harness is the one that does the battery light, so as you already have said you have two yellow wires which are the alternator to rectifier ones; without knowing which make your reg/rec is, my guess it has to be one of the red/white ones from the reg/rec you connect to the red/white in the staggered connector - it seems logical if you compare that thought with the diagram above. Again, not knowing which reg/rec and what you may have connected to the staggered connector - the other wire in the harness in that connector should be a red/black and IIRC live all the time or when ignition is on - it is not used with the RR51 reg/rec but it is used if the OEM reg/rec is fitted. I think some careful trial and error has to be used so you have to try connecting it and see if the light goes out when you start the bike - and switch it off quickly if it doesn't. Before you do that though, try finding out what the two green wires are connected to in the harness as it is obvious from the diagram and the OEM diagram that two wires from the reg/rec connector together into a single connector - which is the wire from the big 30Amp fuse. See below:
Thanks for your help but it seems this reg/rec won't operate the battery light, I've tried connecting the red/white to all 4 wires in the big plug and it won't work, from a bit of research using the wire colours I think the reg/rec is a shindengen SH673-12
I found this on Ducati UpNorth Forum - by Derek who is also a member here. Don't worry that it relates to a 750SS - the wiring is basically the same. '750SS. If it is a carbed one (it must be with a 2-wire alternator) the earth was through the casing of the regulator. A white/red wire went to the warning lamp, a red wire to the battery via the 30A fuse and a red/black returned from the fuse box when ignition on. This red/back wire was to provide voltage sensing for the regulator. The new regulator doesn't need voltage sensing and has no connection for a charge warning lamp. Connect BOTH green wires to earth, preferably straight to the battery, and connect BOTH to the battery +ve, preferably via the 30A fuse. The fuse will protect the regulator if the battery is inadvertently connected the wrong way round. It will also protect the battery and wiring if the regulator becomes faulty and short circuits internally. I have had this happen on a 900S and the regulator practically melted with flames from it.' You could fit one of these - they work well. Eclipse and Monsoon Battery Voltage Monitors - Waterproof Precise Durable | SparkBright
The last two Electrex RR51 regulators I've used on my M900 (virtually identical charging circuit) have had an intermittent generator warning light displaying despite being plugged in correctly and so has become another quirk to learn to live with. Despite not illuminating with ignition on/engine not running, when the last regulator failed (first Electrex) the light did come on permanently (for me its main purpose) but I understand that it's disconcerting not knowing if the bulb is working.
I have a Shindengen Mosfet rectifier, which is great. Also have a battery/charge indicator LED which I can set to battery charge or alternator voltage output. This is what I rely on as its on with the ignition and I know what voltage is by the colour of the LED, highly recommend it.
