RPM Gauge bounces & engine intermittently cuts in & out

Started by WileyRiley, September 17, 2023, 08:43:16 PM

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Hi Everyone,

I'm looking for a little help figuring out the issues with my 86 FJ1200. I posted about something similar last year, and it was suggested to check the infamous red plug from the stator to battery - of which I've changed over to something different. From what I've read, the issue with the red plug can be symptomatic of a bad voltage regulator. Voltage at the battery at 3000rpm is around 15.2-15.6 , I'm hoping to order a new one from RPM soon but they don't have stock. Has anyone used the VR from Rick's Motorsports Electrics??

Also, when on the road, the bikes rpm gauge often bounces, and with that "bouncing" or flickering the bike cuts in and out, almost like you're jerking a really sensitive throttle. On a recent trip, I noticed the fuel gauge was bouncing more than what seemed normal for road conditions and fuel moving around. I read that bouncing gauges can be symptomatic of a bad ground in the gauge cluster - but I don't think it would also cause the engine to intermittently cut in and out like that too, would it?!

This whole thing has me a little stumped and I'm wondering if anyone has experienced and fixed issues like this in the past?


The RPM gauge gets its signal from the ignition. Bouncing and feeling like it cuts out for second, does sound like a ground issue. The fuel gauge no longer has enough damping fluid to slow the bounce.

Some light reading:
The glass is not half full, it was engineered with a 2X safety factor.

'86 Ambulance - Bent frame, cracked case, due for an overhaul
'89 Stormy Blue - Suits my Dark Side


Thanks, FJ Monkey. The bike might have more than one issue. Gauges bouncing, lights flickering, and engine cutting in a out seems to be more prominent under load (was able to confirm this on the center stand while the bike is in gear). Everything I've read seems to point at grounding and/or the rectifier unit - I don't think all of these symptoms can be attributed to the VR. I posted a video on youtube to show what its doing.



I'm having the same issue on my 90. Ignition cutting in and out, I also have lower power, but the bike sat for a long time before I got it. What are your thoughts on the rectifier? I haven't seen anything in my Clymer about that.

Edit: watched your video. Mine will rev up just fine, but will cut in and out if I bounce the bike in the workshop or under load while I ride. On the stand, no rider on it, it revs freely.
1990 FJ1200 6.7k mi Restoration



Sounds like a bad ground, from here.  Ground cables have two ends. Both ends need to be bright shiny metal, and bolted to bright shiny metal, solidly in place. Dull metal is corroded metal. Corrosion is a lousy conductor, and can even be an insulator. The only thing I see as common to all of the problems would be your ground connections.  

Also, it never hurts to string a parallel ground wire along anywhere you have a factory ground wire, with new terminal ends.  These bikes are old, and wires can corrode and break inside the insulating sleeving.

P.S. Life is too short, and health is too valuable, to ride on cheap parade-duty tires.


1988 FJ1200
1991 FJ1200