had a few problems with st4 wasn't revving above 4000 revs with lights on turned out to be corrosion at plastic connection box with three yellow from the altenator to regulator right hand fairing.I came back from holiday took it out now its not revving above 4000 light off or on tried spraying connection again no luck and revcounter doesn't drop with the lights on its charging ok .thinking maybe regulaor.Any ideas
sounds very much like regulator as starts to try to hard when corrosion you mentioned present - often accompanied by overcharging and battery spillage. Are yellow wires ok - 'wriggly' or looking overheated?
A voltmeter connected to battery will confirm if regulator is working as you will see voltage rise as you raise the revs above tickover
funny enough the voltage is riseing up to 6000 before when the light was on it wasn't charging and the rev counter dropped but ok with lights off but was it cleared when I sprayed the connection
Could be reg/rec or alternator, most likely reg/rec... If you change the reg/rec get an aftermarket one (Electrex or similar) as they are cheaper and much better than OEM. Also, the cable that connects the alternator to the reg/rec has a hard life - it tends to get fried by the radiator as it passes very close, and corrosion sets in quite easily. If that cable is degraded it will give the alternator and the reg/rec a hard time, and lead to damage. I ended up making a new one myself, as they are difficult to identify on the Ducati parts list...
Okay but what about now and what voltage readings are you getting at idle and then again with revs raised ?
Well your problem is certainly not due to a lack of volts. I can't remember the safe cut off for raised revs but that sounds a little high . Where is @Denzil the Ducati when you want him?
going to order new rectifier its not regulating power going up to 16s to high will keep everybody posted
Does sound like reg/rec is playing up, but I can't see why that would affect the high speed running.. When was the fuel filter changed? As they block, the load on the pump increases and screws the electrics. It's one reason why the yellow cables burn as the current draw increases.
16 Volts sounds too high to me. Reg/Rec and new cables. That's a great tip @nelly it sounds so simple & logical, but I wouldn't have thought of it in a 1000 years
Thanks a few years back, I had a ST4 with a few issues. One it wouldn't rev past 4 or 5k, second it wasn't charging great and then it randomly cut out and threw up a few errors. Once it was parked up for a while, it would restart and run for a while longer. Charging was the yellow connector and an easy spot. Charging was good. Fuel filter was blocked.... It had picked up a dirty tank full of fuel which tied in with when the bike began to play up. The last one was a 'mare of job. The cable to the pump had burnt out, but inside the loom. It's not really a great gauge yet it's fused at 20A. The cable gave up before the fuse, but not completely. As it got hot, it stopped the pump. As it cooled, it worked again. The fuel filter is the most overlooked service item I come across, yet it can cause so many issues. Steel tanks need doing every year, two at the most. I serviced bikes that have never been done. Early 916 that have been 15+ years old and surprisingly enough the old 2 wire alternator cable has been cut back so far it's needed extending and what's left is like card board.
fuel filter was changed maybe a year or so back ordered rectifier see if it clears it thanks all for advise will let you know outcome
Stuart if your voltage across the battery is over 16v DC (at any revs) the regulator is fecked. The regulators should limit dc voltage to 14.5 or 14.6v dc max, anything over 15 and your battery is at risk. Tick over voltage at around 1100-1200 rpm should be around 14v across the battery but it will drop when the engine and battery are hot from normal running. If you noticed one of the pins in the yellow wire plug was burnt more than the others then your rectifier is probably suffering from an unbalanced supply voltage under load and will be quietly cooking. It will be very hot to touch. The plug contacts have to be absolutely tight and very clean otherwise the regulator will die very quickly. It is better to replace it for something with a high amp rating that can be tightened - never use bullet connectors. Chris, Yuasa recommend nothing over 15.2v to charge the YT12 AGM batteries used on the 996 later 748s
good to hear - I meant to go to Bristol this year but wasn't up to it. Will let you know if heading Avebury way on a bike.
