Charging/electrical question
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Author:  fasterdammit [ Tue Apr 28, 2020 7:53 pm ]
Post subject:  Charging/electrical question

Seems like all I do when I post here is look for help. :dunno:

So I've been having strange running issues with my P750 for a season or so. Most recently, I (finally) did the starter mod, with the extra solenoids last season - and that was amazing. The bike has never started or run so well.

Fast forward, and the running issues crept back in. Long story short, the bike just felt like it was drowning. It couldn't get out of its own way, I'd have to feather the clutch for 100m just to get going from a light. It felt fuel related, but it also felt electrical-related, because every now & then, for a split second, I'd get a burst normal performance.

Which brings me to today: I've got a 2yo AGM battery with a fresh charge - literally 5 minutes between taking it off the charger and putting it in the bike. Here's what happens:

1. Key out of the ignition, I've got 12.4v in the system.
2. Turn the key to run, it drops to 9.9-10.0v on the system.
3. Hit the starter, and I only get clicks from one of the new solenoids.
4. Now I have like 9.6v on the system.

I figured that 9.9-10.0v I saw right off the bat was a bad sign; I didn't think I'd have enough to spin the starter (and I was right, yay me). So I cleaned up the connection for the positive battery-to-starter lead. And I noticed one of the older clips on one of the coils had melted, so I replaced that (wire terminal) well.

When first I tried this the other day the starter tried to turn, and died. That's when I started watching the voltage, and decided I'd make sure the battery was full up before taking another look at it.

So that's where I am. I assume something is eating a lot of voltage right off the bat. Coil? Stator? I don't know what to test next, or how to test it. I do have a DMM, but I'm not sure what kind of voltage I should be looking for, for which component.

Any & all suggestions appreciated.

Author:  Derek [ Wed Apr 29, 2020 8:53 am ]
Post subject:  Re: Charging/electrical question

I think you need a new battery. With the ignition off a good battery should be reading about 12.5V and it shouldn't drop substantially when the ignition is switched on, maybe to about 12.2 - 12.3V. After 15 seconds of cranking and then waiting 5 minutes the voltage should have returned to no less than 12.3V . Although you don't mention time to recover after an attempted start a voltage of 9.6V is not good.

Start with a new battery then check all the connections; battery terminals, solenoid terminals, starter motor terminal, battery to ground connections, I'm not familiar with the 750 grounds but I think there will be more than one of them.
Given the poor state of the battery it's possible that it's not being charged properly.
With the engine running at about 1500-2000 rpm measure across the battery terminals. With a good battery you should be seeing around 14.0V, no more than 14.5V. With a partly discharged battery that's drawing current in an attempt charge it probably a bit less but at least 13.5V and rising. If the charging system isn't achieving this then the battery will fail sooner rather than later.

The melted clip at the coil connection may or may not have been connected to the poor running. It shows that there was a poor connection there, probably due to oxidation, which caused local heat at the connector. So it should definitely have been replaced and the terminal cleaned.
The poor running of course may due to a low system voltage because the battery isn't being charged sufficiently. So I think checking the battery and charging should be your first step.

Author:  angelix [ Wed Apr 29, 2020 5:19 pm ]
Post subject:  Re: Charging/electrical question

P750s are starting to have some age and the first problem with "vintage" looms is that they start to behave weird.

First thing, get yourself a new battery (or borrow one that you know it works) , some contact cleaner and some nice contact grease and start cleaning and lubricating all the connectors.

then follow the grounds and do the same on the frame and the engine; there might be also one ground point at the regulator.

then disconnect the fuel pump , the voltage regulator (including the stator) and the coils, put on a battery and start checking the voltages before and after cranking.

check if it is cranking or not, you just need to verify that side of the circuit.

if there is an issue with the loom most likely will be with one of the 3 systems attached to it (pump, coils and stator/regulator)

my bet is that the regulator is giving the ghost, that is the only thing I think that is connected to the battery without a fuse (or if there is then is quite big)

Author:  higgy [ Thu Apr 30, 2020 1:47 pm ]
Post subject:  Re: Charging/electrical question

I would also recommend not installing a lithium battery till all your charging issues are resolved.Lithium is very sensitive to charging issues

Author:  angelix [ Fri May 01, 2020 8:28 am ]
Post subject:  Re: Charging/electrical question

one word of advise, when you play with looms always do ONE connector at the time, disconnect clean lubricate a reconnect, especially on the old looms.

Moderm looms are fool proof either by color coding or using different connectors so you cannot mix them up.

Old looms sometimes have the same connectors and can be swapped... it happened to me with an SS loom, by the time i realized why it wasn't cranking , I noticed i had the stop switch turned , so i flicked it and 1 second later .....the loom red as a cherry and smoking everywhere and I a nice plastic temporary fuel tank just cms away from it.

total Panic! I nearly died of heart attach especially when I realized that you cannot pull out redhot wires with your bare hands and the more they burn the worse it gets.

yes, I had the big 40amps fuse in place, but by swapping to plugs it got somehow bypassed and not one single fuse blew, only all the wiring.

O managed to grab a set of cutters and cut the positive at the battery, only then the electrical fire stopped, but I still had to grab some rag and put off the plastic melting fires I had all over the bike.

I still have the shivers when I think of the terrifying experience and the smell ... that is something I won't forget ever, I had a cough for 3 days and my eyes were swollen like Rocky balboa's.

Author:  Tamburinifan [ Fri May 01, 2020 11:47 am ]
Post subject:  Re: Charging/electrical question

+1 Derek & higgy`s advice.

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