No start problem diagnosed using WPS-500 and other Pico scope traces.  I thought this would be of interest since both spark and fuel were present and the timing was correct but would not start, why?

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Do you have a voltage and amp trace from the battery/starter motor on a no start.?

I did not measure battery voltage but I did attach a known good battery directly the starter (bypassed the relay and wiring).  Chart #10 is a current trace of the starter for cranking no-start as well as for a known good starter during cranking.

It would have been nice to see the voltage drop on both sides of the starter. (power and ground)

Did a new starter fix this bike.?

Thanks, I should get the power and ground.  I will measure them today.  I have not received the new starter.

I measured the power and ground volts for the KTM no start cranking condition.  Volts look OK but the current draw is very high relative to a known good (see page 10 of the original attachment).

I get a new starter motor in about another week.  Once installed I will verify my diagnosis.

This is my first attempt to share on this site and appreciate any suggestions for improvement in my communication.  I purchased the scope a few month ago but this is my first real use of it, not much time  :-[.

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Sorry I haven't played with any motorcycles with a scope.
What is going on with the in cranking compression tower?


Sheepherder wrote on Dec 31^st, 2013 at 12:01pm:

I purchased the scope a few month ago but this is my first real use of it, not much time

You are going pretty good with it so far :).
Nice presentation.

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Yes it is very nice presentation, but we also like to get the ps.data files, so we can play and do the 3 M’s with our own software.  :)

It seems that your voltage drop is too much. Voltage is what makes the start motor spin/speed.

Anthony,
Not sure about that waveform too, but could it be from the starter motor slowing down.?

This file is from an old Honda CBR1000F.
New battery on top and the old at bottom is reference from the same bike.
Ch D is ground/starter housing.
Notice lower voltage drop and lower amp draw on the new battery.

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I have confirmed the shape of the compression curve on two separate known good KTM-EXC (2007 & 2008).  Both show the same bump as the pressure increases.  I have attached a compression waveform showing what I think is the correct valve timing (not 100% sure of the valve timing).

I don't think the voltage drop during cranking is the problem since I but a known good (high amperage) battery directly on the starter terminals (bypassing the relay and wiring) and got exactly the same low RPM high current starter performance (pickup generator pulse still low on compression stroke).

Thanks for the inputs and discussion  :).

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Problem solved, the "Torque Limiter" was slipping.  I had know idea there was a "Torque Limiter" between the starter and the crankshaft!  The bike now starts with the electric starter.  I have attached an updated pdf file.  I will send the psdata files to anyone requesting them.  Thanks for your interest and comments. :D

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The bump in the compression slope could be caused by the auto compression release. Not sure about it though. They have a centrifical weight on the end of the camshaft and when engine speed is low it keeps one valve open slightly. At least my 09 400 xcw has that set up. Im not sure if my bike has a torque limiter or not but I have about 150hrs/4400miles on mine with no problems. The 400 has lower compression so it may not need the limiter.

Nice job on the write up.

Thanks Chad, I think you are correct about the bump on the compression curve. 

Sheepherder wrote on Jan 4^th, 2014 at 9:57pm:

I had know idea there was a "Torque Limiter" between the starter and the crankshaft!  The bike now starts with the electric starter.

I guess that might explain the tower being unequal.

StitchB