Getting enough juice!

[blink5625]

Hi all,

My love-hate relationship with my 81 continues. I have been having trouble getting this thing started. I got the carbs professionally cleaned with a fancy vibrating machine and new plugs, and the mechanic said that he had no trouble starting it up.

I get home, let it sit for a week, it doesn't start up. Charge up the battery on the tender. Nothing.

So.. last ditch effort: use my truck to jump the bike and VOILA! Starts right up. So... I get a new battery. Charge it for the right amount of time after I put the electrolyte in there and put it in. Try to start the battery... same problem as before. Jump it with the truck. Boom, starts up. Even when I put it on the tender and the battery has a "green light" it doesn't get enough juice.

I did the electric tests for the alternator and rectifier. They came out fine.

1. Any idea what this is? Why does my truck battery start up the bike?
2. Couldn't figure out how to test the voltage regulator with my Haynes manual. Could this be it?
3. The coils were a little off on the secondary winding resistance. 13 instead of 9.5 ohms... I don't think that this could be it because the Haynes manual is not specifically for the '81.

 

[mmmboost]

Sounds like you might have a bad connection creating a lot of resistance. Our tiny batteries don't put out that many amp. Have you checked your connections from the battery to the starter with an Ohm-Meter? If the bike starts with a huge jump from your vehicle, but doesn't with the bike battery with a brand new battery, it's most likely a current problem.

Voltage = Current x Resistance.

If you have a bad connection and the resistance is through the roof...voltage is going to drop and resistance is going to go up as a result.

 

[blink5625]

So say that this is the case-- I'll test it tomorrow. What would the fix be? Thanks mmmboost.

 

[mmmboost]

So say that this is the case-- I'll test it tomorrow. What would the fix be? Thanks mmmboost.

Depends on what the issue is. If you test from one end of a wire to the other with no connections in between, and the resistance is more than a few ohms, then the wire may be damaged or corroded and should be replaced (this is probably unlikely). If you test the resistance across a connector and it's more than a few ohms, then the connections are probably corroded or failing. You can try and clean up the connections with a brass brush and some electrical contact cleaner.

I should mention though that poor connections is just my theory. It's the simplest, easiest, and most likely cause of your problem.......but that doesn't mean it IS the problem. Occam's Razor

A worst case scenario is that it could be an issue with your ignition coils or starter motor.


When you try to start the bike on the bike battery alone, what happens? Does it just turn over slowly? Or does it turn at the same speed as when boosted? Does it try to fire?

 

[blink5625]

When I start it on the bike battery alone, it turns at the same speed when boosted. It actually fires sometimes-- usually on the first try, but then quickly dies.

 

[16VGTIDave]

Check the ground wires from the engine to the battery negative.

 

[blink5625]

Ok-- checked the ground wire... everything seems okay. Does anyone know how important the secondary winding resistance is on the coils? I have a Haynes manual that isn't specific to the 1981 XS400 Special model... but was wondering if this could be it?

I should mention-- if I ride the bike around for awhile, I can get the bike started right away. If I let it sit for a few hours and it gets cold, it won't start without the jump.