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DR650SE Engine cuts out every second at steady throttle. Fork dive at each hiccup

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My unmodified 1998 DR650 cuts out every half second when the throttle is held steady between 1/8 - 1/2 open. The affect is pronounced long enough to cause the front forks dive at each hiccup. The only time there is no cutout is with a throttle opening greater than 3/4+ (ie, 85 MPH +), or strong acceleration or during idle (idling in gear is strong, too). Also, the cutouts disappear whenever frequently varying the throttle - as on a dirt trail. When street or highway, when the throttle opening is held steady guning the throttle will break these horrible steady state cut-outs, but sometimes the cutout is so stuck the engine remains bogged for 1-2 seconds; an unnerving period at freeway speeds. All carburetor internals are stock and the carb body is very clean. The intake is unmodified beyond a missing airbox snorkel. Exhaust is stock. ODO 15,000 miles and previous owner did not disclose this problem at sale.

Attempts at fixing.

  • Cleaned carb twice - each time the engine ran fine for 30 minutes then resumed the problem the next day.
  • Tried shimming the needle 0.5mm - nothing.
  • Removed carb fuel filter - no change.
  • Checked for air leaks between diaphragm and carb cap - none.
  • CV carburetor air cleaner is an oil soaked rag - plenty of air movement.
  • Cold engine - OK, no cutouts even without choke.
  • Adding choke while warm - no improvement in cutouts, engine dies as expected.
  • Shut off the fuel petcock while cruising to drop carb float level - no noticeable improvement before dead engine.

Carburetor Settings

  • Not a vacuum petcock
  • Emory clothed the plastic slide - CV slide drops smoothly.
  • Carburetor needle float level - high side of 0.54-0.62"
  • Pilot - 2 1/2 turns out
  • Needle 6F23 - stock
  • Pilot Jet 42.5 - stock
  • Main 140 - stock
  • Air Jet 1.00 - stock
  • Right side vent - uncapped
  • Charcoal purge port, bottom - capped
  • Charcoal vacuum port, top - capped

Engine condition

  • Clean air filter
  • Valves adjusted
  • Spark plugs gaped and clean
  • Electrical connections checked and cleaned - no improvement
  • Altitude 4500'
  • regular gas

Any help would be appreciated. I've owned this bike for only this summer and have only been able to off road. On-road is the pits! Thanks

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IMHO ignition related: either bad coil, TCI box, pickup sensor or hidden intermittent contact somewhere.

bastard to find when they go on and off....

start by checking that resistance for coil and pickup are within spec

 

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Yes, the problem has been traced to the ignition and operation is returned to normal using a replacement coil/ wire/ boot set. The bad unit tested with a very high resistance between spark plug boots. But, further testing of the old unit relieved my fear something fried my coil. Bare wire secondary coil resistance was 4.5k ohm. This indicates it was not a coil issue but a problem with the boot to cable connection. Could have saved a few bucks trimming the high tension leads and re-inserting the spark boots into clean wire. Thank you so much for the out side of the box suggestion!

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Cut outs started again, as before, after a long stretch of highway on a warm day. Something had me put the spurs to the side stand. It was the side stand switch all along. Over 20 hours of pulling carbs and researching problems. I had no cut outs while off roading like other owner’s sidestand problems.

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