magna vf750 intermittent start

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  #1  
Old 06-27-08, 08:39 PM
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magna vf750 intermittent start

This is a intermittent, yet consistent problem. I can only start the bike once each day. I'll start it, shut off the ignitition and then when I go to start it again, it won't fire. However, the next day that I go to troubleshoot the problem, it always will start on the first go. I replaced one of the coils due to corrosion, and one of the pulse generators is out of tolerance by 10%. I welcome any help!
 
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  #2  
Old 06-28-08, 05:52 AM
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Check each side for spark when in a no start. If a spark in one side and not the other, I would check connections/replace that coil. If no spark on either side, I would check connections for continuity, but the CDI module would be high on the list.

What year are you working on?
 
  #3  
Old 06-28-08, 07:57 AM
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Since the fault is somewhat reproducible you have a good chance of finding this.
I'd hook up several monitoring LEDs through series resistors to crucial points. Not running is easier to fix than running poorly.
 
  #4  
Old 06-28-08, 02:14 PM
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It's a '82 magna. What specifically is the CDI module? I mean is there a capictance that is being charged and then discharged to start the bike the first time, but then not being able to recharge to start a second time, but then over time its able to accumulate a large enough charge?
 
  #5  
Old 06-29-08, 09:23 AM
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The activity of the CDI module is ongoing. It allows for timing adjustments pertaining to rpms of the engine and the capacitor discharge function. The capacitor is charged, then signaled to discharge with each plug firing. From CDI it goes to the coils for the high voltage spark generation.

However, your bike, as an '82, doesn't show the module. Those modules or CDI boxes showed up on the later models - mid to late 80's.

About anything electronic or electricity driven is sensitive to heat deterioration. Most are dealing with a great deal of heat - internal as well as environmental. Consequently, things may work when they are cold, but as soon as they warm to operating temperatures, they start acting up or fail altogether. Ignition modules, coils, batteries, etc., all show this characteristic. With yours, the suspect parts would be the coil and components of the signal generator.

What you're asking about the ability to recharge the capacitors could very well be the problem, but it could be for a number of reasons. There's quite a few components in that system to have to be working. As a rule the capacitor setup charges very quickly, which is one of the advantages of the capacitor design for high rpm engines.

Switches and other connection devices have to be checked out first as a basic troubleshoot. A lot of times electronic components can be checked by a parts store for you prior to replacement.
 

Last edited by marbobj; 06-29-08 at 10:23 AM.
  #6  
Old 07-02-08, 06:08 PM
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Great, thanks for your help.
 
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