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Author Topic: Minimum cranking speed with CDI (Honda)  (Read 4599 times)
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generatorshovel
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« on: November 23, 2015, 07:56:21 PM »

I have a problem , no spark !
Iv'e rebuilt the 250/4 Honda, and it's tight, cranking speed is way down , and will remain so until it runs a few minutes , the electric starter motor is typical Honda, built "just" powerful enough to do the job, with a stock engine,(most times)
At the start line before the last run I had a lot of trouble getting it to fire, so I had suspicions something may have been on the way out electrically, possibly the starter ?
I threw a bare crankshaft into a spare set of crankcases, starter & associated drive / spark generators in place, and spun it, with the race bike CDI plugged into the "test" engine, SPARK !
Tested the impedance of both sets of  spark generators (hall effect?) , both sets within specs, I also checked while spinning engine(s), impedance rose with revs, the "test" engine spins abnormally quick, as it only has a crank to spin (no rods/ primary drive) I think (by ear) the rebuilt engine spins below 250 rpm when cranked.
Does the average CDI unit have a minimum cranking speed for the spark trigger event to happen ?

Tiny
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Tiny (in OZ)
I would prefer to make horsepower, rather than buy, or hya it, regardless of the difficulties involved , as it would then be MINE
TheBaron
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« Reply #1 on: November 23, 2015, 08:24:36 PM »

I'm not sure about a minimum speed,,,, but they sure do have a Minimum Voltage in order to fire....

A starter turning slow is a sure fire way to draw more Amps than normal, and that can drop the voltage below what the spark box has to have in order to fire the plugs...

take out all the sparkplugs and plug them into the caps with the threads grounded and spin it over and see if the plugs are firing without fighting the compression...

Good luck,
Robert
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generatorshovel
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« Reply #2 on: November 23, 2015, 08:35:56 PM »

I have 2 batteries in the test setup, one for ign, and another for cranking, separated circuits, I did have voltge drop using one, even though it's 3 times amp hr capacity of the original in the bike, this contributed to the lack of spark ( no spark below 11 volts)
With the separate systems, there's no voltage drop in the ign circuit at all.
Thanks Robert  cheers
Tiny
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Tiny (in OZ)
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RansomT
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« Reply #3 on: November 23, 2015, 09:14:25 PM »

For what it is worth, Suzuki does have a min. 400 rpm, IIRC.
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« Reply #4 on: November 23, 2015, 09:59:10 PM »

Could also be the commutator is worn and shorted in spots.  Ran into that with a Corvair a number of years back.  It turned slow, created a lot of heat, and drew huge power on cranking. 

With little load - ie, no rods or pistons - you'd likely not notice the draw down, but under a true load, you'll suck that battery down like a cold beer on a hot day in the hay loft.
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« Reply #5 on: November 23, 2015, 10:14:52 PM »

The first thing I do is clean and retighten the engine, battery, and coil grounds. The ignition coils on the new Triumphs have poor quality grounding and it often results in a problem like you describe.  They were replaced with Nology coils that has a big braided wire grounding straps.  That fixed the problem.
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generatorshovel
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« Reply #6 on: November 23, 2015, 10:51:56 PM »

For what it is worth, Suzuki does have a min. 400 rpm, IIRC.
Thanks Mr T
Could also be the commutator is worn and shorted in spots.  Ran into that with a Corvair a number of years back.  It turned slow, created a lot of heat, and drew huge power on cranking. 

With little load - ie, no rods or pistons - you'd likely not notice the draw down, but under a true load, you'll suck that battery down like a cold beer on a hot day in the hay loft.
Yeah, your right Conrad, I have 2 complete setups for the testing, I'll test pickups in engine #2 1/2 next, once I remove the "difficult to access" from engine #1, then I'll swap a few starter motors to see if I can get #1 engine cranking speed up, Ideally, by then I will know how slow I can spin the engines and still produce spark.
As usual, life has a habit of getting in the way,,,
The first thing I do is clean and retighten the engine, battery, and coil grounds. The ignition coils on the new Triumphs have poor quality grounding and it often results in a problem like you describe.  They were replaced with Nology coils that has a big braided wire grounding straps.  That fixed the problem.
Thanks Bo, that was the 1st thing I checked, it seems as though the power supply to the coils is remaining uninterrupted while cranking,,no powerusinteruptus,,no spark
Tiny
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Tiny (in OZ)
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generatorshovel
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« Reply #7 on: November 24, 2015, 07:29:41 PM »

Yup, there's a cranking speed minimum for the spark event to happen,,,,,,
Swapped starters,,problem cured,,spins like a a Hippy @ Woodstock now, with a healthy blue spark !

Tiny   grin
« Last Edit: November 30, 2015, 12:05:44 AM by generatorshovel » Logged

Tiny (in OZ)
I would prefer to make horsepower, rather than buy, or hya it, regardless of the difficulties involved , as it would then be MINE
generatorshovel
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« Reply #8 on: November 30, 2015, 12:06:13 AM »

 grin

 cheers
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Tiny (in OZ)
I would prefer to make horsepower, rather than buy, or hya it, regardless of the difficulties involved , as it would then be MINE
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« Reply #9 on: December 21, 2015, 02:36:12 AM »

Tiny, EFI bikes need to be above a certain RPM--at least these dang Suzukis we use--even a spot in ECU Editor to enable big block starting which lowers that threshold. And really need good battery voltage during cranking to make sure there is a spark. Working on Busa right now with fresh top end with a bump in comp that would spark like mad with all plugs out of motor, but back in, not so much. New battery on the way, already been through entire starting system.
Had a really hi-compressioin 1630 Busa that had a 24 volt start system, and if one battery was not as happy as it should be bike would spin over well but not spark--- drove me crazy.
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