Starter problems 650 Maxim

I have been trying to start the bike with a car battery with jumper cables connected directly to the battery cables on the bike. I measured the voltage on the battery @ 12.8 volts and it drops to below 9 volts with the starter cranking and it won't fire. I put the battery on a charger for a few minutes and the voltage goes up to 13.2 or so and the bike starts like it should and the voltage drops to 10.5 while cranking. This battery easily starts a car at 12.8 volts after sitting for weeks. I took the bike starter apart and it was just a little dirty in the part where the brushes are and like new everywhere else. One brush was 12mm long and the other was 10.5mm. I got the bike 10 years ago with 5300 miles on it and it now has 12700 miles. It had the original tires on it so I imagine the starter hasn't ever been touched.

 

If the starter is drawing excessive amps and previously it wasn't then it needs maintenance. ie a kit or a commutator resurface and cleanup.
If the starter draws so much that it is making the battery drop below 10v(i think) then you will have issues with the TCI actually firing the plugs so... dead end!
Refurb and get it spinning nice and freely.

 

when voltage drops below ~10 volts bike will not start because tci will not fire below ~10 volts.

could be bad battery or starter needs rebuild. sounds like you need a starter rebuild by what you say about the car battery
it could also be a solenoid with burnt contacts check voltage drop on output side of solenoid too.
solenoid could be on the way out due to excessive current draw from starter.

test voltage drop on both solenoid bolts and at starter connector bolt. clean the connections at battery and solenoid could be dirty or corroded connections

 

I measured the voltage at the battery while trying to start the bike. If the battery just came off a charge it had 13.5 volts and it would start. Voltage was over 10 volts while cranking. If the battery was sitting for a few days, there was 12.8 volts on the battery, it would drop into the 9's while cranking and the bike wouldn't start.

There is continuity between the adjacent sections on the commutator, you can't see or feel a ridge on it from where the brushes rub and don't rub. The brushes are in spec(8.5-12mm per the book) and the bearings fit nicely. There is a 1 volt drop on the battery when I use jumper cables to test the starter. The battery I am using easily starts a car(350hp 396) but it just clicks when I try to start the bike. Is there a way to test the plate the brushes sit in and can I hook the jumper cables directly to the starter on the bike just to see if it will spin the engine?

 

yes just do not start car

sounds like a bad battery to me, with the voltage droping over a few days

 

It's an older battery but it starts the car with 12.2 volts.

 

How are the brushes supposed to fit? Mine are rounded to the shape of the commutator and the new set is flat. I think there's enough material on the used brushes to file the mating surface flat. Would that make it work?

 

But it drops below what the TCI needs in order to provide spark while cranking the motorcycle over.

The XJ TCI needs at least 10 volts to start, and a bit more to start reliably.

The voltage drop that you're seeing is consistant with a battery that is past its useful life as a starting battery.

 

The brushes will mate to the commutator as the starter motor runs. That process hardly takes any time at all.
They will not, and should not, stay flat.

The same is true of the alternator brushes mating to the alternator slip rings, though they should have very little curve to them.

On the topic of charging voltage; what is the voltage at the battery once the bike is running (no jumper cables attached)?
Measure at idle, at 2,500 RPM, and at 4,000 RPM.

 

I checked it a few months ago and don't remember the exact numbers but I had the repair manual out and remember being glad it was all within the range the book said.

 

New brushed did the trick. Just need to drain the 2 year old gas, get a new battery, and fire it up. Thanks for all the help.