shadow 500 problem

Hi, a friend has an 85 Shadow 500, runs good at idle,but as soon as it hits
2000 rpm, in neutral or in gear, the tach drops to 0 and the engine runs
real rough,no power,can barely get 30 mph flat out...had the carbs done,
new plugs.The problem only occurs when the tach stops working......any ideas
on what to try next?
Thanks,
Rodger

 

A lot of bikes have the tachometer linked to the electronic ignition, if
it's an electronic tach, of course.

I'd start with the connections to and from the tach.

If it's a cable tach.... erm, no idea.

 

Yes, it is an electronic tach,am gonna start checking the wires ..thank
you...

 

You seem to have the symptoms backward. The ignition control unit
counts pulses from the ignition pickup coils. The electronic tach stops
working when the ignition control unit doesn't get pulses (or gets weak
pulses) from the ignition pickup coils. Check the connector where the
pickup coils plug into the motorbike's wiring harness, check the
connector on the ICU itself, and hook up a DC voltmeter to see if you
get erractic 12 volts DC when the engine is revved up. If you see that,
then it's a problem with the ignition switch or the kill switch or some
safety interlock switch like a sidestand, neutral, or clutch switch...