'84 FJ has a cut-out issue after 4k RPM

[tboy]

Tim in Oakville here:   
Just finished restoration on my '84.  Frame-out with a refreshed motor.
For the first ride it ran flawlessly, but on the return leg, the bike started to be choppy or missing, but would kick back in and run smooth intermittently. 
Slowing down to leave the highway,  it ran fine under 4K rpm. 
**During the cutting out - the tach jumps correspondingly
Subsequent test rides, it has the same symptom  -  runs smooth at moderate speeds then cuts in/out.

Looking for a direction on where the issue might be.

Thanks very much

[Pat Conlon]

Hi Tim, kudos on your beautiful bike

The jumping tach is a key so I would suspect something ignition related.
1) Check your battery connections. Check the main ground to the engine.
2) Check and clean your right side run/stop switch. The circuit thru that switch powers your ignition box.
3) Check your key ignition switch for intermittent readings. Wiggle key, wiggle wires.
4) Pull apart all your plug connectors and clean them. Check the infamous RED PLUG connector. Don't just visually check the outside of the plug, pull it apart and look at it.
5) Ohm check all grounds (black wire) especially those which power your coils... Wiggle them at the connectors, see if the reading changes.
6) Voltage check on all the 12v power supply wires, wiggle them.
7) Disconnect the plug at the ignition box which feeds your ignition pick up coils, ohm check each pick up coil (you have 2) at that plug. You should read 149 to 182 ohms when the coils are warm at 68*f.

That should get you started. I had a similar problem on my '84 and it was (finally) traced back to the run/stop switch.
Intermittent electrical problems are a bitch.

Cheers  Pat

[Pat Conlon]

The side stand switch can get dodgy but I don't think it's the problem. In my experience, either it works or it doesn't. I've not heard of an intermittent high rpm failure caused by a sidestand switch.
You could unplug the pig tail on the sidestand switch and put a temporary jumper on the male prongs to close the circuit and take a ride to see if that helps.

[fj johnnie]

Nice bike. Did you powdercoat the frame? If so my first guess would be along the lines of Pat's reply. Check grounds. I restored an 86 as well and had to sand the powdercoat at ground locations .

[twangin4u]

 Is the battery new? Bike looks sweet so I'm guessing that's a yes.  Maybe check out some of the relay mods for bypassing the puny stock wires to your could

[balky1]

And the most stupid suggestions of all - did you check the spark plugs?