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I have a 2000 Vstar 650 here. I have weak spark on front cylinder only. I have gone through the manual and tested every component in the no spark troubleshooting guide. I have replaced the ECU with OEM new and the relay box where the diodes live. The spark coils are new and have battery voltage at the red/black wire. The orange wire to ECU tests good, no excessive resistance and not shorted to ground. One strange symptom is that the front cylinder has spark but will not sustain running. The pipe heats up so I know the fuel is burning but it feels as if it's ignighting on the exhaust stroke. I have pulled the flywheel and checked the key way. I really am out of ideas now.
 

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Was the bike running normally and then something happened and it quit?

or did you obtain the bike in its present condition?

Weak spark is difficult to characterize, unless you can put some kind of meter on it and measure something. I dont know how to do that.
 

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It is a customer's bike, I am told last time he rode all was well and a few days later would not start.
 

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I would check the compression to make sure something hasnt failed on a valve or ring

I assume you checked it with a new spark plug, it would be odd for his plug to fail and then you happen to pull a bad plug out of a new box.

The timing advance on the 650 .... 2000? Im not sure what controls that. I know on the later years the throttle position sensor advances the timing, Im not sure a 2000 has one, or maybe Im thinking of the shutoff solenoid? If the carb has a position sensor and it fails that will tell the ECM to push the timing out in the weeds.

The only other thing I can think of is whatever is on the flywheel that tells the ECM the position of the crankshaft - is there one point for the rear cylinder and the front is always X degrees away, or are there two magnets or something on the flywheel that triggers the ECM, one for the front and one for the rear cylinder?
 

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This bike has 2 hall effect sensor pads milled into the fly wheel. Both in good shape and sensor ( pulse coil) tested good. 1plus volt ac at start rpm.
 

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I second the compression check. You stated there's spark. We assume fuel is good. If you have spark and fuel you need compression to complete the combustion stoke. Healthy engines should have compression over 100 psi per cylinder. I'm a little confused as you said weak spark then you said you have enough spark to fire and produce exhaust pipe heat. One way to test weak spark is with a spark tester like pictured below. Open it up way up, if spark jumps gap you have good sparks. Can actually do same thing with spark plug, just open gap up really wide. Keep us informed on findings.

 

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Discussion Starter #7
Compression is good on both cylinders.
To clarify my primary issue is a weak, badly timed spark on the front cylinder and zero spark on the rear.
Tomorrow I will test the spark of the front with the tool shown I am sure I have one somewhere.
I will also look for a TPS, there was no mention of a TPS test in the manual but it is something to address either way.
 

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Hope this helps.
 

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When you said you have a weak spark on the front, I assumed you had a good spark on the rear cylinder - my mistake.

If you have 12V going where its suppose to go, make sure the ground wires are good and cleanly attached to the frame. People always check the 12V wires and forget the return path back to the battery.

That spark tester is very interesting, I have never seen one before, now I want one.

Also check the ground wire to the battery from the frame, and check the voltage on the battery (at the ECM if you can) while its running.

Something that happens frequently on bikes with electronic ignition, when the battery voltage drops (old battery) the ECM does not have enough voltage to fire the plugs. It does not get weaker and weaker, it hits a lower threshold level and just shuts off.

Its possible the battery is right on the edge while running.
 

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That spark tester is very interesting, I have never seen one before, now I want one.
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They work great. Old school. Last forever. Easy to use. Any auto parts store should have them.

 
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