Question about Yamaha XV 535 Virago DX Motorcycles

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92 virago 750. Front cylinder runs intermittently. Coil is good. I cleaned carbs. Suspect CDI. Seems to run fine until it warms up. I recently put new Voltage Regulator in. Stator is not shorted. and Charge circuit is fine. After warm up starts to miss and then back fires loud!. I've even run tank of seafoam. Seems to run okay above 3,000 rpm. How can I prove its the CDI? Or could it still be carbs?

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  • dale_mattiso Oct 07, 2010

    Actually its a TCI box. P# J4T032. I'm gonna inspect TCI box and look for moisture and bad solder joints. I've been checking all external feeds. Both pick up coils are ~ 5.2 Ohms. The TCI has two connectors. The 4 pin connecter only has two wires. They measure 222 ohms cold and 260 ohms @ operating temp. Cleaned kick stand switch and checked clutch switch. Had 12 volts at all other terminals for igniter.(orange and grey wires). Started up yesterday. Idled nicely for 5 mins. Rev"d up smoothly as well initially. Thought I fixed. (Nope) shut off, put on the helmet, started up and drove off; less then 1/2 mile starts to miss on front cylinder

  • dale_mattiso Oct 07, 2010

    Since it ran fine initially, I don't think its a carb issue, to include diaphrams. Wouldn't missfire be more of a constant failure if it was the diaphram?

  • dale_mattiso Oct 08, 2010

    If the TCI checks out okay, Would you suspect the pickup coils? Where are the pick up coils located? I know the stator is located on left crank case cover. Are pickup coils close to or attached to the stator?

  • dale_mattiso Oct 11, 2010

    Solved! It was either a pickup coil wire shorting to ground or bad connection at TCI. I finally got a good understanding of circuit. The pickup coil wires may have been shorting to motor casing. I did over heat bike at Sturgis this year. May have melted insulation some. So I simply moved wiring harness



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You have to test all the electronics on the bike to figure out if you have a bad CDI box. A CDI box can test good and still be bad. Your problem sounds more like a bad spark plug cap. Unscrew the cap from the end of the wire and take an OHM reading on the cap. If it is higher or lower than 5000 OHMs replace the cap . A plug cap from NGK runs about $5. Replace them both for about $10 it should take care of the problem.

Posted on Oct 04, 2010

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  • dale_mattiso Oct 05, 2010

    Ohmed out and Swapped plug caps. Still same problem. Does stator coil create voltage for spark plugs? Bike ran good until it warms up then problem appears. I get spark out of plug cap. Even when warm. Just don't know if its enough to fire cylinder? Only thing left is CDI and the Stator... Right? I don't have service manual. Been searching the webb. Any Ideas?

  • David Belcher
    David Belcher Oct 05, 2010

    Unbolt the CDI box and turn it over. If there is a small weep hole on the bottom and there is any indication of moisture at that point, you will probably need a new CDI box. Certain models of Virago had this defect it is possible you have an affected model. There was never a recall or acknowledgment of a problem. On some boxes a hole was put there to let moisture escape. Unfortunately, it actually helps cause the internal corrosion in the CDI box. Typically electronic components fail as they get warm. Your stator is probably OK but it is possible the loss of spark could be a pulsar pick up that malfunctions. Inspect the CDI box but test all the components first before you replace the CDI (we want to be sure because CDI boxes are expensive and a used one may have the same problem) The stator charges the battery but it does not directly run the coils. The power to run the bike comes from the battery. If it still sparks when it is warm, all you need is fuel, air, and spark(there is no way of measuring weak). Have you tried switching the diaphragm pistons in the carburetors to see if the rubber diaphragm is the cause of the issue?

  • David Belcher
    David Belcher Oct 07, 2010

    Just threw out the possibility , Thought the inspection of the front carburetor might not be too hard to double check. A small crack or pin hole may not be an issue till you get out on the road and warmed up. Intermittent problems can be real head scratchers. I do remember several parts customers with Virago's having moisture get into the box through a tiny drain hole that caused internal (out of sight ) corrosion that affected the CDI's performance.

  • David Belcher
    David Belcher Oct 08, 2010

    The pulsar pickups are with the stator , outside the flywheel. You can find a free downloadable service manual at this site:



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Pls be informed that due to my current rank and rating, even a Helpful would be detrimental to my status. Should this solution not address your concern, it would be appreciated if you could just not rate it at all. Cheers.

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