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Discussion Starter · #1 ·
After taking the carbs off twice for a leaking float valve, I went on a 10 mile ride. Everything seemed normal and when I went back out the tack seemed to display rpm X 2. ????????
 
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RPM X2? Do you mean it seemed to indicate it was running twice as fast? Like say when it should have down 6,000 RPM, it was indicating redline?

Or am I off the mark?
 

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Did you recently mess with the instrument panel or change any electrical connections dealing with the ignition?

30+ years ago I built a Heathkit tachometer for my 1st car, 62 Nova convertable. The tach kit could be wired for use on 4, 6, or 8 cylinder engines. The only difference was how/where you connected the input wire (and maybe the ground wire?). So if the 500 tach is similar, & uses circuitry allowing for 1, 2 & 4 cylinder engines... maybe a wire is hooked up wrong.

But I've been fooled comparing car experiences w/ motorcycles before... so...

Just a thought.
 

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Discussion Starter · #7 ·
Nope, just toook everything apart for a carb issue. Of course, I was moving a bunch of electrical stuff while I was doing that. I didn't unplug anything.
 

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Does it only do it at Idle or also while riding the bike? Could you have possibly exposed a wire somehwere that is screwing with the electricity? Maybe you choke is on? Perhaps the idle adjustment got messed with accidently. Check that. I mean ****, on choke my bike idles around 3.5k if I remember correctly. It's been about 7 months since I've seen the bike sooo. Just check everything you can think of and I'm sure you'll find something is screwed.
 

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If the choke is reving the engine to 3k+ push it forward a tad to get it under 2000.
Putting it in gear at high revs makes one heck of a CLUNK. (Does that do any damage?)
 
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MrSciTrek said:
If the choke is reving the engine to 3k+ push it forward a tad to get it under 2000.
Putting it in gear at high revs makes one heck of a CLUNK. (Does that do any damage?)
I know how the choke works but thanks. It just happens to be cold up in alaska at the beginning and end of summer so the choke is needed sometimes. I doubt that putting it in gear with the choke hurts anything. It can't be much worse than clutchless shifting at much higher rpms.
 

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bhd1223 said:
MrSciTrek said:
If the choke is reving the engine to 3k+ push it forward a tad to get it under 2000.
Putting it in gear at high revs makes one heck of a CLUNK. (Does that do any damage?)
I know how the choke works but thanks. It just happens to be cold up in alaska at the beginning and end of summer so the choke is needed sometimes. I doubt that putting it in gear with the choke hurts anything. It can't be much worse than clutchless shifting at much higher rpms.
Sorry about stating the obvious. Y'see I teach 8th graders & while many of them are actuall approaching college level of thinking, there are others who... well. Y'know?
So stating the obvious is important if they are to have any shot at catching onto something a bit trickier. It just has to be done in a way that keeps the swifter kids involved. Tricky.
 

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Discussion Starter · #12 ·
OK guys, one more time. The engine idles normal. say at 1000 rpm. But the tach reads 2000 rpm. If I'm going down the road where it should be normally at 3000 rpm (and is) the tach reads 6000 rpm. I'm pretty sure it's electrical, but I don't have the manual yet to trace the wiring. I just thought someone had run into this and could give me a quick answer. I has nothing to do with the choke or actual idle speeds or actual rpm's. It starts and runs and idles fine, just the tach shows the rpm's twice as much as the actual rpm's. Hench, tach X 2
 

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I think the tach knows the RPM by picking up on 1 coil.

It may be reading from both coils now ? It really seems like an electrical problem. Look for worn out shielding on the wires.

It's the first time I hear about this problem..
 

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Discussion Starter · #14 ·
I looked at a schematic and looks like it gets its signal from the left coil only. I'll have to pull the tank and see what I can find.
 

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If the tach pick-up wire passes very close to, or touches, the other plug wire maybe it's picking up a second signal through induction.

Anyone know if the tach sensor gets its signal by induction or by a resistor-protected direct connection, or some other method?
 

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The wiring diagram says it's a direct connection. Altough it's a bit different for different models (like A1-A6 etc.).
I'm highly positive to the fact that the tach is getting another signal from the other coil :p
 

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Follow the green and white wire.

FOG
 

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Discussion Starter · #19 ·
My boy got home last night from a Faith Hill concert @3:00AM, got on the bike to come home, and the tach reads fine, as it does now. Didn't do a thing. ???????????? Well, if it happens again, I'll have a direction to go. Thanks all.
 
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