Odd running when power to brush?

bobber33

bobber33

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Been over this entire bike (new bobber build minimal wiring)
This is a 1980 with TCI.
Bike starts and runs fine with the no power going to the brush with the brown wire.
As soon as power is applied to the brush the bike starts to sputter and cough.
If i give it any throttle it spits and pops.
With no power to the brush throttle response is fine and everything seems normal?
(except it wont charge of-course)

Tested the stator wires, seem fine.
Just replaced the Rotor (i was told the pickup magnet was weak), didn't fix my problem.
Regulator has been tested and swapped with another one and same problem?
The only parts on this bike now that are NOT new are the Stator, Pickup, and TCI box...

Any ideas what the hell is going on here?
Why would my charging system affect the way the bike runs?
:confused:
 
There's obviously miswiring in your minimal wiring. See what the battery voltage does when you connect to the brush.
 
Can u elaborate on what may be miswired? ive been over the entire thing and everything looks legit...
With the brush wire plugged in the battery voltage goes up when throttle is applied to about 13.5 give or take, because its hard to get it to rev up without falling on its face.
But literally as soon as i pull the brush out it's fine...
wiring is like this
wire.jpg
 
Interesting. Look at the voltage on the brush both before and after you connect it. And on the rotor.
 
I've run a jumper as well directly from the brush screw and positive battery and same thing...
 
Just another thought as this thing is starting to get annoying...
Is there any chance the pickup coil is getting messed up by the magnetic field created by the rotor/stator when power is applied?
Because when the charging system is disabled the bike runs fine.?

Does anyone have any similar experience with a bad pickup?
:banghead:
 
That's way too esoteric. It's a dirt and grit problemo. Measure the wire before and after you attach it to the brush. Measure resistance from everywhere to ground. There will be a wrong voltage on one side that goes to both sides when you connect it. That will tell you what's at fault. You have an '80 stator I presume?
 
xjwmx said:
That's way too esoteric. It's a dirt and grit problemo. Measure the wire before and after you attach it to the brush. Measure resistance from everywhere to ground. There will be a wrong voltage when you connect it. That will tell you what's at fault. You have an '80 stator I presume?
Click to expand...

As far as i know its the original stator.
Pickup has the slotted top hole for adjustments as well.
But is there any explanation for the way it effects the way the bike runs? Charging or not it should run the same unless the battery dies....
So this leads me to the only other part on the stator which is the magnetic pickup...
But how do i test it?
 
You're thinking of it as if it was wired correctly, but it isn't. The pickup isn't the problem, it isn't even in the circuit just in the same physical area. But to test it it's 7-800 ohms or so from each coil to the common (black?) connection.
 
xjwmx said:
You're thinking of it as if it was wired correctly, but it isn't. The pickup isn't the problem, it isn't even in the circuit just in the same physical area. But to test it it's 7-800 ohms or so from each coil to the common (black?) connection.
Click to expand...

Thanks...
I'll go over the wiring again, but there are only a few wires on this thing, and nothing is crossed between charging and ignition circuits.
That's why its confusing... makes no sense how one can screw up the other when they have nothing to do with each other....
 
The final thing would be to trace every single wire with your ohm meter. Not too involved since there isn't a lot of wiring. Print the schematic out and mark each wire out once you've tested it. If that checks out, the schematic is no good. Before that, make sure each of the 7 grounds is going to the frame.
 
xjwmx said:
The final thing would be to trace every single wire with your ohm meter. Not too involved since there isn't a lot of wiring. Print the schematic out and mark each wire out once you've tested it. If that checks out, the schematic is no good. Before that, make sure each of the 7 grounds is going to the frame.
Click to expand...

OK so EVERY wire has been gone over and nothing is wrong with the wiring... striped this thing to nothing. Got rid of the electric starter and solenoid too.

This may be interesting though.. i didn't really notice before but when the bike is COLD
it charges fine and runs perfect - 1- 2 minutes of idling in the garage and then the problem occurs. Stops charging and sputters and coughs if throttle applied.
So something gets messed up when HOT? Again if i disconnect the power wire to the brush it smoothes back out and runs fine even when hot?
Only parts left are the pickup the tci box and the stator that haven't been swapped out.
:banghead:
 
I don't know if you can do this, but maybe you can. Take a test clip and put it on the loose brush wire. With the engine running let the other end brush lightly against the rotor on the ring the brush is supposed to ride on. Don't lose a finger or let the wire get away. If the bike doesn't mess up then something is funny with the brush mount on the stator, which you say is a normal '80. I'd stay with the brush-caused issue rather than chasing the cold vs hot issue.

The very best thing you could do is find out what the voltages are supposed to be at every connection and check them, but it might be hard to get that info together.

So at this point you have to have a bad schematic or a bad part because the wiring follows the schematic. The only parts you haven't substituted are the stator and the tci. The stator might develop a problem when it's warm. Let it warm up good and then give it the normal stator test. The tci I think is less likely to have a problem that the brush affects.
 
Last edited:
OK just did this, took out the brush from the mount. Held it so nothing was touching the stator.
Have power going to the brush from jumper.
If i slide the brush in (without letting it touch anything around it) and it touches the rotor ring instantly the bike stumbles....(again engine is hot.. stator is HOT)
So same issue...
 
Ok, then do a stator test when the stator is hot. 10 ohms or so from whites to whites and the rest, it's in the manual.
 
I'm gonna post a video in a second of what its doing as soon as the brush hits the rotor...
Hold on a second
 
OK so here is a quick iphone video of what's happening.
NOTE this doesn't happen when the bike is cold.
The pop you hear is the carb spitting when the brush is inserted.
I was holding the throttle with 1 hand and the brush with the other.
So it was hard to reach everything...
Girlfriend holding camera so i hope you can get the picture...

click on this link to check out the video
http://www.theoryfx.com/STUFF/brush.MOV
 
+1 on stator or wires to stator grounding when hot. Put the hot for the ignition on a separate battery so you can start testing the charging circuit?
 
Well, there's a load on the motor when the brush is connected because then it's driving a generator with a load on it. So I hear in the video the motor slowing down a bit when the brush goes in which may be normal.

Might be that you just need to do a good tuneup with the brush attached and the motor warmed and see what you get.
 
xjwmx said:
Well, there's a load on the motor when the brush is connected because then it's driving a generator with a load on it. So I hear in the video the motor slowing down a bit when the brush goes in which may be normal.

Might be that you just need to do a good tuneup with the brush attached and the motor warmed and see what you get.
Click to expand...


Its hard to tell from the vid, but the bike just coughs and sputters and backfires when charging system is engaged. (again only when hot, when cold it charges and runs fine)
Everything on this bike is NEW. And it runs amazing, other than this problem.
The problem is something in the charging system is affecting the ignition system... which again leads me to the pickup coil.
Rotor/stator create an electro magnet, pickup coil is also magnetic, so if not this the only other thing in the TCI box, but generally they work or don't correct?
 

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