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Starting issues & battery voltage drop

Electrical

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Old Aug 22nd, 2010, 08:48 PM     #1
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Starting issues & battery voltage drop

1988 Softail / FXSTC

When starting you have to bump the starter button serveral times before the motor will turn over and start. Once it's started it runs great.
  • load test on battery and it passed
  • voltage test on battery while running about 14volts
  • when you try to start bike battery will drop down around 9 volt or below
    (while your bumping start when it won't turn motor over)
  • installed new starter & solenoid
  • new battery cables for both Pos & Neg
  • tested starter relay and OK
  • check timing and is as per factory spec
  • tested vacuum advance and it tested OK
  • battery test at 12.8 volts sitting
  • new ignition switch
  • Ohm wiring path from starter relay thru main breaker thru solenoid thru main switch thru starter button thru ignition switch
  • Ohm starter button & main switch
  • doesn't matter whether it's hot or cold
  • new coil & spark plug wires last couple of months
  • rebuilt carb in the last couple months
  • this is the 3rd starter in the last 2 yrs
  • jumped battery from car and it didn't make a defference you still had to bump starter till it would turn over
test main breaker

Need help don't know what else to check and wife on butt about bike not running
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Old Aug 22nd, 2010, 08:58 PM     #2
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Re: Starting issues & battery voltage drop

wow got me stumped looks like u did w/ i would have checked...good luck...itll take smarter than me witch should not take long..
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Old Aug 22nd, 2010, 09:12 PM     #3
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Re: Starting issues & battery voltage drop

I would determine if the problem is electrical or mechanical first. I would put a torque wrench on the compensator sprocket and measure the parasitic drag of the entire assembly. You must determine if the load the starter is seeing is normal or excessively high for some reason.

Measure and see how much torque is required to turn the engine. Once you eliminate that from the equation, it should not be too difficult to determine what is happening.

Would you happen to have an inductive amp probe to measure your cranking current. That is also a must to know after you determine what your parasitic drag is. You can buy adapters to be used with a quality multi meter.
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Old Aug 22nd, 2010, 09:27 PM     #4
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Re: Starting issues & battery voltage drop

I am not as well versed as Hoop at the reddy...but my bet is the battery voltage dropping to 9V is a dead giveaway...something is dropping that voltage, could still be a bad battery or the starter draw is too high, your 10.5VDC threshold for your ECM and Ignition System to fire the plugs. I would bite the bullet and get a new battery. If you ever allowed the old battery to fully discharge over it's lifetime, the voltage reserve degrades. If you do that several times, your battery may "test" okay, but in practice not deliver.

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Last edited by NEWHD74FAN; Aug 23rd, 2010 at 01:07 AM. Reason: Added Links to Schematics
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Old Aug 22nd, 2010, 10:05 PM     #5
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Re: Starting issues & battery voltage drop

NWHF,

'88 Softtail (FXSTC).

TQ
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Old Aug 22nd, 2010, 10:06 PM     #6
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Re: Starting issues & battery voltage drop

Your right NewHD, he may have a ton of current draw with that kind of voltage drop. Something sure is not right. Either a bad battery or too much current draw due to possible engine drag.

The reason I even suggested engine drag was because he said he was on his 3rd starter. Unless they are poor quality re-mans, something has to be taking them out. (?)

Either way. With a few tools and measurements, it should not be too hard to iron out.
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Old Aug 22nd, 2010, 10:08 PM     #7
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Re: Starting issues & battery voltage drop

what is the range of Ft Lbs that is acceptable on the compensator sprocket for the parasitic drag?

inductive amp probe to measure your cranking current / what is the acceptable range that this should be?
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Old Aug 22nd, 2010, 11:53 PM     #8
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Re: Starting issues & battery voltage drop

I am basing these numbers to my 2009 96. With both plugs removed and the coil secondary grounded, I have seen no more than 50 cranking amps when the engine is cold. And I would bet at least 6 amps of that is ignition and lights. Without compression against the starter, your engine should spin very freely. My guess (for your size engine) 45 amps tops for current draw. I also have load tested my battery to 200 (more than 1/2 CCA) amps on several occasions and the voltage stayed well above 10 volts. Mind you I did not hold it for 15 seconds because I was not actually load testing my battery, but I did see at least a 4:1 ratio of "required" amps vs "available" amps.

I would then reinstall the plugs (secondary still grounded) and test the current draw one more time with compression. Collect and record some data. See if it jumps way up.

For your size engine I would Guess using a Beam torque wrench, the torque required to Break stationary friction will be something like 30 ft/lbs tops engine cold with plugs out, bike in neutral. If it was more than that at the CRANK with engine Cold, I would look into why.

I realize we are dragging the clutch pack w/ the crank but I have seen Big block V8's only have 80 ft/lbs at the harmonic so I would be concerned if I saw much more than 30 ft/lbs. More exact numbers would only apply to my 96.

Hopefully not too many engineering changes in starters exist between mine & your model.
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Old Aug 23rd, 2010, 01:14 AM     #9
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Re: Starting issues & battery voltage drop

That is great info even if ballpark. Nice to know.

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Old Aug 23rd, 2010, 09:23 AM     #10
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Re: Starting issues & battery voltage drop

Quote: Originally Posted by Hoople View Post
Hopefully not too many engineering changes in starters exist between mine & your model.
Hoople/others; I hope I'm not muddying up the diagnostic waters here, but there's a big difference in the starters. 1988 was the last year of the old type that had a separately mounted solenoid. As usual, I'm not much help electrically, but my shovel had the same type starter, and had the symptoms described. Turned out my inner primary had a crack that allowed starter to bind slightly. FYI, I'm attaching pics of old/new starters. A quick place to get info about various starter specs. is ebay "harley starter motors". Sift through listings.
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Starting issues & battery voltage drop-shovel_starter.jpg   Starting issues & battery voltage drop-evo_starter.jpg  
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