finding the starter wiring problem

I've got the common slow starter problem. I've checked and cleaned all bullet connections and grounds, ruled out solenoid, have a new battery and new starter brushes. The only way i can get it to crank normally is to disconnect the battery and hook up a car battery.

Help an electrically challenged person with an analog multimeter find the problem. The bike battery seems to be good, its new and only drops to about 9-10 volts when cranking. I presume I must have a hard to find bad connection or high resistance building up somewhere. But where?

Perhaps not ironically, this has been an issue when the bike is warm ever since i got it 10 years ago. In fact when I went to test ride it they had a car battery hooked up from the rear rack, which is why I happened to have the cables handy to test it with a car battery today. But it usually cranked OK when cold.
 

Hi 82KZ
It sounds to me like this could be one of five things

1. you say you have replaced the battery but 9-10v sounds low even when cranking ( I wouldn't expect it to get lower than 10v)
2. A high resistance in the positive ( connect the negative side of your voltmeter to the positive terminal of the battery and the positive side of the meter to the positive terminal on the starter - this will measure PD (potential difference)  when cranking. The difference should read no more tha approx 0.5v. A high reading shows a resistance in the starter positive supply from the battery through the solenoid)
3. A high resistance in the earth return ( connect the negative side of your voltmeter to the negative side of the battery and hold the positive meter lead against the body of the starter, when cranking the reading should be no more than approx 0.3 v. A higher reading here means a poor connection between the starter body and the engine or a poor connection between the engine and the battery negative Terminal)
4. the starter itself may be faulty ( although you have re-bushed it the torque of the motor is dictated by the condition of the internal windings, with age the insulation breaks down when hot and some of the windings short out which reduces the torque produced by the motor)
5. Finally don't rule out a mechanical fault (is the engine "nipping" when hot, have you tried turning it over by hand from the end of the crank with a ratchet to see if is tightening up when hot ?)

Your starter solenoid internal switch conacts can be burnt out and resist against the current flow.
Try to short cut the solenoid in/out terminals at the nuts with a pliers.
The battery negative wire connector point to the frame/engine surface should be as clean as possible.
A low voltage like 12 Volts dont like any resistens (Ohm). Any single extra Ohm drops the voltage/ampere and the power (Watts) to the starter.
OHM´s law U = R * I      Power (Watts) = U * I , so less U (volt) or less I (ampere) flow = less Power to the starter motor.

If bridging the solenoid solves the problem, it is worth carrying out the positive and negative tests I have described on the switch live and earth to the solenoid before you replace it. If the voltage is low through the primary side of the solenoid (the switching side) the magnetic field it creates in the solenoid (which is what pulls the contacts together) will be weak. This will mean the contacts aren't pulled together tightly and the new solenoid will start to burn up as the contacts will arc. Eventually you will have the same problem again. Hope this helps

Ahh thanks guys but you may be too late. Left to my own devices I've gone on to break other things already.

I was just guessing when I said voltage was dropping to 9 to 10v when it cranked. I only had an analog meter and that's pretty hard to get an accurate voltage reading on. It might have been 10+ v.  Now I bought a digital meter but it doesn't crank anymore.

Although I had it cranking with the car battery, I walked away for a few days and when I cam back it wouldn't crank even with the car battery. I then jumpered the solenoid/relay and it cranked, but I think I jumped it too long and burned out the starter. It will not spin now, even with 12v applied to the starter on the bench. So I gotta get that fixed before I can resume testing. I'm inclined to replace the solenoid too, just in case. I mean I've already thrown a lot of good money after bad so another 20 bucks isn't going to break the bank and it will eliminate one more possible source of problems. And maybe resistance in the solenoid was the problem all along (and maybe not...my crude testing with the analog meter showed it was throwing pretty near 12v at the starter). I've triple checked all the wiring, connections and grounds

 

If the bushings are worn out the starter will drag.
Steve

Well I had the starter gone thru and the brushes replaced a couple weeks ago, so I would hope they evaluated everything. But they will be going through it again tomorrow.

To answer an earlier question, no, I do not notice it getting harder the longer I turn the crank by hand.

OK, now we are cranking! Not sure if it was the solenoid or starter or both, but the starter guy soldered something saying it's possible low voltage caused a problem in the starter that he fixed. And I replaced the solenoid and it cranks like new now off the bike's new battery. But I'm still struggling with points and timing. 

Glad you got it sorted